Major interaction on record — check this product against your medications before combining. Based on 5 of 6 ingredients. Check your meds →
Dietary supplement

8 Hour Unflavored Ingredients & Drug Interactions

by Muscle Feast

8 Hour Unflavored label
See full label image
Powder Category: Other Combinations
Most serious interaction: Major
Clinical methodology reviewed by · Updated Sep 16, 2026 · Label data from the NIH DSLD
What is this page for?

First and foremost: checking 8 Hour Unflavored against your medications. The heart of this page is the interaction checker and the full interaction report — how this product’s ingredients may interact with prescription and over-the-counter medicines you may be taking.

Around that, we add a pharmacist’s high-level view of the product as a whole — what’s inside, the evidence for its stated use, how transparent the label is, and what safety data exists — so you can see the full picture in one place. It’s educational information from our licensed clinical databases and the clinical staff at HelloPharmacist — not medical advice — and we don’t sell or endorse products. Our editorial policy

The interaction bottom line Most serious interaction: Major

8 Hour Unflavored is a dietary supplement by Muscle Feast with 6 active ingredients. Its ingredients are commonly taken for mental alertness and reducing fatigue, improving athletic performance, headache and migraine relief.Based on those ingredients, 770 medications have a known interaction with it, the most serious rated major. The ingredients most likely to interact are Caffeine Anhydrous, Vitamin B-6, L-Taurine. Use the checker below to test your specific medication, or read the full HelloPharmacist Interaction Report.

Jump to a section

Check Your Meds Against 8 Hour Unflavored by Muscle Feast

Ask about any prescription or over-the-counter medication and we check it for interactions with 8 Hour Unflavored by Muscle Feast — and tell you which ingredient is responsible.

Pharmacist-reviewed data Checks every ingredient Answer in seconds
Prefer a human? Send your question to our licensed pharmacists — free, answered by email within 24 hours.

HelloPharmacist Scorecard of 8 Hour Unflavored by Muscle Feast

Our pharmacy team’s full take, with four database checks built into the cards below — a summary of what is known, not a grade of the product itself.

From our pharmacy team — supplement deep dive

Generated from HelloPharmacist’s pharmacist-curated databases and editorial rules · Last generated Jul 12, 2026

What’s inside

Full disclosure
Ingredient Transparency · database check
Full

Every active ingredient lists its own amount on the label.

Why this rating?
  • The label discloses an exact amount for 6 of its 6 active ingredients.
  • No proprietary blends here — you can verify the dose of every single component.

Muscle Feast's 8 Hour Unflavored is a 6-ingredient powder built around caffeine anhydrous (a concentrated form of caffeine), which is the main active component. The other active ingredients are L-Taurine (an amino acid), L-Tyrosine (another amino acid), Vitamin B-3, Vitamin B-6, and Vitamin B-12.

These B vitamins support energy metabolism. The product contains no inactive ingredients listed.

Does it work?

Strong evidence
Evidence for Intended Use · database check
By FDA rules, dietary supplements can’t claim to treat, cure, or prevent disease — so labels speak in careful marketing language. We discern each product’s intended use from its name, label claims, and label statements, then grade the clinical evidence for that use. How these ratings are computed
Strong

Clinical evidence supports at least one of this product's ingredients for its stated purpose.

Why this rating?
  • The label markets this product for: Long-lasting energy and improved focus.
  • We looked for evidence on: Athletic performance, Attention, Attention deficit-hyperactivity disorder (ADHD), Cognitive function, Cognitive impairment, Fatigue — and 3 related terms.
  • The strongest evidence on file: Caffeine is rated "Likely Effective" for Athletic performance (Natural Medicines).
  • Also on file: Caffeine is rated "Likely Effective" for Mental alertness.
  • Also on file: Tyrosine is rated "Possibly Effective" for Cognitive function.

Caffeine in this product is effective for neonatal apnea (a breathing condition in newborns) and postoperative headache. It's likely effective for boosting mental alertness and athletic performance.

For other uses like bronchopulmonary dysplasia (a lung condition in premature infants), caffeine is possibly effective. L-Taurine is possibly effective for certain liver and heart conditions but possibly ineffective for weight loss.

L-Tyrosine is effective only for phenylketonuria (PKU), a rare metabolic disorder; for cognitive function and memory it's possibly effective, but for athletic performance it's possibly ineffective. For L-Tyrosine's effects on alcohol use disorder and dementia, the evidence isn't established in our data.

Vitamin B-6 is effective for certain types of anemia, B-6 deficiency, and a rare seizure disorder; it's likely effective for high homocysteine levels and possibly effective for pregnancy-related nausea. Vitamin B-12 is effective for certain rare conditions and B-12 deficiency, likely effective for cyanide poisoning, and possibly effective for canker sores and nerve pain.

We don't have effectiveness data on file for Vitamin B-3.

The evidence, ingredient by ingredient Caffeine Taurine Tyrosine Vitamin B6 Vitamin B12

How safe is it?

Well-documented data
Safety Information · database check
Well characterized

Adverse-effect, pregnancy, and general safety data are on file for most of these ingredients.

Why this rating?
  • We hold adverse-effect (side-effect) data for 5 of the 5 matched ingredients.
  • Pregnancy & breastfeeding safety ratings cover 5 of 5.
  • General safety write-ups exist for 5 of 5.
  • Remember: this measures how much safety information exists. Thin data is not the same as being safe.

Caffeine is generally well tolerated in moderate amounts for healthy adults, though high doses can cause serious side effects. Most common side effects are anxiety, dependence with regular use, diarrhea, headache, insomnia, tremors, nausea, and restlessness.

Rarely, stroke has been reported. High caffeine intake is linked to pregnancy risks; ask your doctor about safe limits.

Small amounts pass into breast milk; moderate intake is usually considered acceptable but can affect the baby. L-Taurine is generally well tolerated short-term in healthy adults, but long-term safety is less certain.

Common side effects are constipation, diarrhea, and indigestion. Rare serious effects include hypersensitivity reactions.

Taurine is likely safe in pregnancy and lactation. L-Tyrosine is generally well tolerated with no serious documented adverse effects; common ones are fatigue, headache, heartburn, and nausea.

There isn't enough safety data for pregnancy or breastfeeding—talk to your doctor. Vitamin B-6 is safe at normal food and supplement amounts, but high doses over time can damage nerves.

Common side effects include abdominal pain, allergic reactions, headache, heartburn, nausea. At high doses (over 1,000 mg daily) it can cause sensory neuropathy (nerve damage).

It's likely safe in pregnancy and lactation at recommended amounts. Vitamin B-12 is generally very safe with no established upper limit; excess is removed in urine.

It's likely safe in pregnancy and lactation and is needed during both. We don't have adverse effect or safety data on file for Vitamin B-3.

Side effects, ingredient by ingredient Caffeine Taurine Tyrosine Vitamin B6 Vitamin B12

Meds to double-check

Major interaction found
Known Interaction Concern · database check
Major identified

At least one ingredient has a documented Major-severity interaction. Check your medications for a personalized result.

Why this rating?
  • 5 of the 5 matched ingredients can interact with medications — Vitamin B12, Vitamin B6, Caffeine, Taurine, Tyrosine.
  • The most serious interaction on file is rated Major.
  • Some involve high-stakes drug classes: anticoagulant / antiplatelet drugs; diabetes medications; lithium; Parkinson's medications.
  • For scale: 770 individual medications appear in the full list. A big number alone doesn't make a product dangerous — what matters is whether YOUR medication is on it, so run yours through the interaction checker on this page.

Before taking this product, double-check if you use ephedrine (Major severity), or any of these: sedatives like pentobarbital, blood-thinning stress-test drugs like dipyridamole, the antipsychotic clozapine, seizure medications (phenobarbital, carbamazepine, phenytoin), blood pressure medications, the heart rhythm drug amiodarone, antacids with cimetidine, quinolone antibiotics, thyroid hormone, levodopa for Parkinson's, lithium, or metformin for diabetes (all Moderate or Minor severity). Use the medication checker on this page with your full prescription list.

Check your own medication Run your meds through the checker above

The bottom line

Scorecard at a glanceFully disclosed formula with clinical evidence supporting its stated purpose. Major medication interactions have been identified, and safety information is well characterized.

This is a stimulant-focused energy powder centered on caffeine, with added amino acids and B vitamins. If you take blood pressure medication, seizure medication, antipsychotics, sedatives, thyroid hormone, levodopa, or metformin, you need to check your exact medications against the tool below before using it.

Talk to your pharmacist about whether the caffeine and other ingredients fit your health and any medications you're on.

Educational only — not medical advice; always confirm with your pharmacist. Our editorial policy · How we use AI

Assessment coverage: 5 of 6 active ingredients matched to our full ingredient reviews (monographs). Based on the product label dated Feb 23, 2022.

This Scorecard evaluates available label information, ingredient evidence, and known medication-safety considerations. It does not independently verify product identity, purity, potency, contamination, or manufacturing quality. How these ratings are computed

At a glance

General information

Key facts about 8 Hour Unflavored, straight from the product label.

Brand Muscle Feast
Net contents 10.58 Oz(s); 300 Gram(s)
Market status On market
Date entered into DSLD Feb 23, 2022
DSLD ID 260311
Product type Other Combinations
Supplement form Powder
Dietary claims / uses All Other, Structure/Function
Intended target group(s) Vegan, Vegetarian, Adult (18 - 50 Years), Women (not pregnant or lactating), No Allergies, Gluten Free
From the label
Everything in this section is reproduced from the manufacturer’s own product label — it’s the label speaking, not HelloPharmacist. We show it so you can see exactly what the maker states; we don’t verify or endorse those statements.

Supplement Facts

The label details for 8 Hour Unflavored by Muscle Feast, sourced from the NIH Dietary Supplement Label Database.

Supplement Facts

Daily Value (DV) Target Group(s):
Adults and children 4 or more years of age
Minimum serving Sizes:
1.5 Gram(s)
Maximum serving Sizes:
1.5 Gram(s)
Servings per container
200
IngredientAmount% DV
Caffeine Anhydrous135 mg--
L-Taurine675 mg--
L-Tyrosine675 mg--
Vitamin B-36 mg3%
Vitamin B-66 mg30%
Vitamin B-1212 mcg300%

Other ingredients: None

Tap any ingredient to jump to its full detail below.

Label statements
These statements are the manufacturer’s wording, reproduced from the product label — the label is saying it, not HelloPharmacist. We don’t verify or endorse them.
Formula

Muscle Feast 8 Hour is unlike other energy drinks that give you jitters followed by sudden crashes, we have formulated 8 Hour with taurine and tyrosine to offset those burdensome side effects.

Suggested/Recommended/Usage/Directions

Suggested use: As an adult dietary supplement, take one serving (1.5g) in 8 ounces of water to help improve energy and focus. Do not consume more than 3 servings in a 24 hour time period. Mix 1 level (1.5g) scoop with 8 oz. water or beverage of choice.

Formulation

Gluten free Soy Free Non-GMO

Certified Vegan American Vegetarian Association

Long-lasting energy Improve focus & cognition

Allergies: None.

Seals/Symbols

Made in our GMP Compliant Facility Made in an FDA Registered Facility Certified Vegan AVA American Vegetarian Association

General Statements

SDVOSB Service Distributed Veteran Owned Small Business

Ohio family owned business

FDA Statement of Identity

Dietary Supplement

Storage

Keep tightly closed in a cool, dry place away from sunlight.

Precautions

Keep out of reach of children

Do not exceed the recommended dose. Consult your physician before using this product. Do not use this product if you are pregnant or nursing. Do not use this product if you are taking any prescription medication.

Do not use this product if you are under the age of 18

Warning: This product is manufactured in a GMP compliant plant that processes milk.

FDA Disclaimer Statement

This statement has not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.

Is this label outdated? Report a formula or label change and our pharmacy team will review it.

See for yourself

8 Hour Unflavored by Muscle Feast label

The label scan from the NIH Dietary Supplement Label Database. Tap to enlarge.

8 Hour Unflavored label

Label images are published by the NIH Dietary Supplement Label Database for the version of this product on file. Always read your actual product label.

View the full label (PDF)
What’s inside

The Ingredients in 8 Hour Unflavored by Muscle Feast

These are the 6 active ingredients this product is made of. Select any to open its full monograph.

Serving size1.5 Gram(s) Dosage formPowder Servings per container200 Amounts shown are per serving.

Most supplement products combine several ingredients, and a medication can interact with the product through any one of them. Each ingredient below shows whether it has known drug interactions.

Caffeine Anhydrous

Interacts with
655 drugs
135 mg per serving

Caffeine is a natural stimulant found in coffee, tea, and many other plants and products. In moderate amounts it can boost alertness and reduce tiredn...

Caffeine Anhydrous monograph & interactions

L-Taurine

Interacts with
173 drugs
675 mg per serving

Taurine is an amino acid your body makes naturally and that you also get from animal foods. It is widely used in energy drinks and sports supplements,...

L-Taurine monograph & interactions

L-Tyrosine

Interacts with
21 drugs
675 mg per serving

L-tyrosine is an amino acid your body uses to make brain chemicals like dopamine and norepinephrine. Some studies suggest it may help mental performan...

L-Tyrosine monograph & interactions

Vitamin B-3

6 mg per serving Form: Niacin

Vitamin B-6

Interacts with
210 drugs
6 mg per serving Form: Pyridoxine Hydrochloride

Vitamin B6 (pyridoxine) is an essential water-soluble vitamin that your body needs for metabolism, brain function, and making red blood cells. It is b...

Vitamin B-6 monograph & interactions

Vitamin B-12

Interacts with
20 drugs
12 mcg per serving Form: Methylcobalamin

Vitamin B12 (cobalamin) is an essential nutrient your body needs to make red blood cells, keep nerves healthy, and support DNA. Supplements are very h...

Vitamin B-12 monograph & interactions

Other (inactive) ingredients: None. These complete the product’s ingredient list but are not active constituents.

Interaction report

8 Hour Unflavored by Muscle Feast Drug Interactions

Want to check YOUR meds against 8 Hour Unflavored?

Ask about interactions with your drugs in plain English — “Can I take it with lisinopril?” — and we find you the answer in seconds, ingredient by ingredient.

 Go to the checker
770Drugs
8 Major 601 Moderate 161 Minor

Ingredients driving the most interactions

Caffeine Anhydrous 655
Vitamin B-6 210
L-Taurine 173
L-Tyrosine 21
Vitamin B-12 20

Individual Drug Interactions

The ingredients in 8 Hour Unflavored interact with 770 drugs. Click any drug to see the details.

5 of the 6 ingredients in 8 Hour Unflavored interact with drugs. Each result below shows which ingredient is responsible. Caffeine Anhydrous Vitamin B-6 L-Taurine L-Tyrosine Vitamin B-12

Each ingredient & the kinds of drugs it affects

For each ingredient in 8 Hour Unflavored with known interactions, here are the types of medications they can affect. Open any type for the detail — or search your exact drug in the checker above.

Caffeine Anhydrous41 drug types · 655 drugs

Ephedrine

Theoretically, concomitant use might increase the risk for stimulant adverse effects.
Use of ephedrine with caffeine can increase the risk of stimulatory adverse effects. There is evidence that using ephedrine with caffeine might increase the risk of serious life-threatening or debilitating adverse effects such as hypertension, myocardial infarction, stroke, seizures, and death.

Likelihood Probable Evidence D
Adenosine (Adenocard)

Theoretically, caffeine might decrease the vasodilatory effects of adenosine and interfere with its use prior to stress testing.
Some evidence shows that caffeine is a competitive inhibitor of adenosine and can reduce the vasodilatory effects of adenosine in humans. However, other research shows that caffeine does not seem to affect supplemental adenosine because high interstitial levels of adenosine overcome the antagonistic effects of caffeine. It is recommended that methylxanthines and methylxanthine-containing products be stopped 24 hours prior to pharmacological stress tests. However, methylxanthines appear more likely to interfere with dipyridamole (Persantine) than adenosine-induced stress testing.

Likelihood Possible Evidence B
Anticoagulant/Antiplatelet Drugs

Theoretically, caffeine may increase the risk of bleeding if used with anticoagulant or antiplatelet drugs.
Caffeine is reported to have antiplatelet activity. Theoretically, it might increase the risk of bleeding when used concomitantly with these agents; however, this interaction has not been reported in humans.

Likelihood Possible Evidence D
Beta-Adrenergic Agonists

Theoretically, large amounts of caffeine might increase the cardiac inotropic effects of beta-agonists.

Likelihood Probable Evidence D
Carbamazepine (Tegretol)

Theoretically, caffeine might reduce the effects of carbamazepine and increase the risk for convulsions.
Animal research suggests that taking caffeine can lower the anticonvulsant effects of carbamazepine and can induce seizures when taken in doses above 400 mg/kg. Human research has shown that taking caffeine 300 mg in three divided doses along with carbamazepine 200 mg reduces the bioavailability of carbamazepine by 32% and prolongs the plasma half-life of carbamazepine 2-fold in healthy individuals.

Likelihood Possible Evidence D
Cimetidine (Tagamet)

Theoretically, cimetidine might increase the levels and adverse effects of caffeine.
Cimetidine decreases the rate of caffeine clearance by 31% to 42%.

Likelihood Likely Evidence B
Clozapine (Clozaril)

Caffeine might increase the levels and adverse effects of clozapine and acutely exacerbate psychotic symptoms.
Caffeine might increase the effects and toxicity of clozapine. Caffeine doses of 400-1000 mg per day inhibit clozapine metabolism. Clozapine is metabolized by cytochrome P450 1A2 (CYP1A2). Although researchers speculate that caffeine might inhibit CYP1A2, there is no reliable evidence that caffeine affects CYP1A2. There is also speculation that genetic factors might make some patients more sensitive to an interaction between clozapine and caffeine. In one case report, severe, life-threatening clozapine toxicity and multiorgan system failure occurred in a patient with schizophrenia stabilized on clozapine who consumed caffeine 600 mg daily.

Likelihood Possible Evidence B
Dipyridamole (Persantine)

Theoretically, caffeine might decrease the vasodilatory effects of dipyridamole and interfere with its use prior to stress testing.
Caffeine inhibits dipyridamole-induced vasodilation. It is recommended that methylxanthines and methylxanthine-containing products be stopped 24 hours prior to pharmacological stress tests. Methylxanthines appear more likely to interfere with dipyridamole (Persantine) than adenosine-induced stress testing.

Likelihood Probable Evidence B
Disulfiram (Antabuse)

Theoretically, disulfiram use might increase the levels and adverse effects of caffeine.
Disulfiram decreases the rate of caffeine clearance.

Likelihood Probable Evidence B
Diuretic Drugs

Theoretically, using caffeine with diuretic drugs might increase the risk of hypokalemia.
Caffeine, especially in excessive amounts, can reduce potassium levels due to stimulation of the sodium-potassium pump. Diuretics can also cause lower potassium levels.

Likelihood Possible Evidence D
Estrogens

Theoretically, estrogens might increase the levels and adverse effects of caffeine.
Estrogen inhibits caffeine metabolism.

Likelihood Probable Evidence B
Ethosuximide (Zarontin)

Theoretically, caffeine might reduce the effects of ethosuximide and increase the risk for convulsions.
Animal research suggests that caffeine 92.4 mg/kg can decrease the anticonvulsant activity of ethosuximide. However, this effect has not been reported in humans.

Likelihood Possible Evidence D
Felbamate (Felbatol)

Theoretically, caffeine might reduce the effects of felbamate and increase the risk for convulsions.
Animal research suggests that a high dose of caffeine 161.7 mg/kg can decreases the anticonvulsant activity of felbamate. However, this effect has not been reported in humans.

Likelihood Possible Evidence D
Flutamide (Eulexin)

Theoretically, caffeine might increase the levels and adverse effects of flutamide.
In vitro evidence suggests that caffeine can inhibit the metabolism of flutamide. However, this effect has not been reported in humans.

Likelihood Probable Evidence D
Fluvoxamine (Luvox)

Theoretically, fluvoxamine might increase the levels and adverse effects of caffeine.
Fluvoxamine reduces caffeine metabolism.

Likelihood Probable Evidence D
Lithium

Abrupt caffeine withdrawal might increase the levels and adverse effects of lithium.
Caffeine has diuretic activity. When abruptly discontinued, caffeine may alter the clearance of lithium. There are two case reports of lithium tremor that worsened upon abrupt coffee withdrawal and 6 case reports of elevated serum lithium levels after reducing or eliminating caffeine intake. In one case, a male with schizoaffective disorder stabilized on lithium had an elevated lithium level after reducing his caffeine intake by 87%. At a later date, he increased his caffeine intake by 6-fold, resulting in a subtherapeutic lithium level and a recurrence of psychiatric symptoms.

Likelihood Probable Evidence D
Monoamine Oxidase Inhibitors (Maois)

Theoretically, concomitant use might increase the risk of a hypertensive crisis.
Caffeine has been shown to inhibit monoamine oxidase (MAO) A and B in laboratory studies. Concomitant intake of large amounts of caffeine with MAOIs might precipitate a hypertensive crisis. In a case report, a patient that consumed 10-12 cups of caffeinated coffee and took the MAOI tranylcypromine presented with severe hypertension. Hypertension was resolved after the patient switched to drinking decaffeinated coffee.

Likelihood Possible Evidence D
Nicotine

Theoretically, concomitant use might increase the risk of hypertension.
Concomitant use of caffeine and nicotine has been shown to have additive cardiovascular effects, including increased heart rate and blood pressure. Blood pressure was increased by 10.8/12.4 mmHg when the agents were used concomitantly.

Likelihood Probable Evidence B
Pentobarbital (Nembutal)

Theoretically, caffeine might decrease the effects of pentobarbital.
Caffeine might negate the hypnotic effects of pentobarbital.

Likelihood Possible Evidence B
Phenobarbital (Luminal)

Theoretically, caffeine might reduce the effects of phenobarbital and increase the risk for convulsions.
Animal research suggests that caffeine can decrease the anticonvulsant activity of phenobarbital. However, the exact mechanism of this interaction is unclear.

Likelihood Possible Evidence D
Phenylpropanolamine

Theoretically, phenylpropanolamine might increase the risk of hypertension, as well as the levels and adverse effects of caffeine.
Concomitant use of phenylpropanolamine and caffeine might cause an additive increase in blood pressure. Phenylpropanolamine also seems to increase caffeine serum levels.

Likelihood Probable Evidence B
Phenytoin (Dilantin)

Theoretically, caffeine might reduce the effects of phenytoin and increase the risk for convulsions.
Animal research suggests that caffeine can decrease the anticonvulsant activity of phenytoin. The effect does not seem to be related to the seizure threshold-lowering effects of caffeine. However, the exact mechanism of this interaction is unclear.

Likelihood Possible Evidence D
Pioglitazone (Actos)

Theoretically, caffeine might increase the levels and clinical effects of pioglitazone.
Animal research suggests that caffeine can modestly increase the maximum concentration, area under the curve, and half-life of pioglitazone, and also reduce its clearance. This increased the antidiabetic effects of pioglitazone. However, the exact mechanism of this interaction is unclear.

Likelihood Possible Evidence D
Quinolone Antibiotics

Theoretically, quinolone antibiotics might increase the levels and adverse effects of caffeine.
Quinolones (also called fluoroquinolones) can decrease caffeine clearance by inhibiting cytochrome P450 1A2 (CYP1A2) enzyme.

Likelihood Probable Evidence B
Riluzole (Rilutek)

Theoretically, concomitant use might increase the levels and adverse effects of both caffeine and riluzole.
Caffeine and riluzole are both metabolized by cytochrome P450 1A2 (CYP1A2), and concomitant use might reduce the metabolism of one or both agents.

Likelihood Possible Evidence D
Caffeine Anhydrous full monograph & all 41 interactions

Vitamin B-65 drug types · 210 drugs

Amiodarone (Cordarone)

Theoretically, vitamin B6 might increase the photosensitivity caused by amiodarone.
Despite initial case reports suggesting that pyridoxine may have a protective effect against amiodarone-induced photosensitivity, preliminary clinical research suggests that pyridoxine may actually exacerbate this adverse effect.

Likelihood Possible Evidence B
Antihypertensive Drugs

Theoretically, vitamin B6 may have additive effects when used with antihypertensive drugs.
Research in hypertensive rats shows that vitamin B6 can decrease systolic blood pressure. Similarly, clinical research in patients with hypertension shows that taking high doses of vitamin B6 may reduce systolic and diastolic blood pressure, possibly by reducing plasma levels of epinephrine and norepinephrine.

Likelihood Possible Evidence B
Phenobarbital (Luminal)

High doses of vitamin B6 may reduce the levels and clinical effects of phenobarbital.
Preliminary clinical evidence suggests that vitamin B6 200 mg daily can reduce plasma levels of phenobarbital, possibly by increasing metabolism. It is not known whether lower doses have any effect. Advise people taking phenobarbital to avoid high doses of vitamin B6.

Likelihood Possible Evidence D
Phenytoin (Dilantin)

High doses of vitamin B6 may reduce the levels and clinical effects of phenytoin.
Preliminary clinical evidence suggests that vitamin B6 200 mg daily can reduce plasma levels of phenytoin, possibly by increasing metabolism. It is not known whether lower doses have any effect. Advise people taking phenytoin to avoid high doses of vitamin B6.

Likelihood Possible Evidence D
Levodopa

Vitamin B6 may increase the metabolism of levodopa when taken alone, but not when taken in conjunction with carbidopa.
Vitamin B6 (pyridoxine) enhances the metabolism of levodopa, reducing its clinical effects. However, this interaction does not occur when carbidopa is used concurrently with levodopa (Sinemet). Therefore, it is not likely to be a problem in most people.

Likelihood Unlikely Evidence D
Vitamin B-6 full monograph & interactions

L-Taurine2 drug types · 173 drugs

Antihypertensive Drugs

Theoretically, taurine might increase the risk of hypotension when taken with antihypertensive drugs.
Some clinical evidence suggests that taurine can reduce both systolic and diastolic blood pressure.

Likelihood Probable Evidence D
Lithium

Theoretically, taurine might reduce excretion and increase plasma levels of lithium.
Taurine is thought to have diuretic properties, which might reduce the excretion of lithium.

Likelihood Probable Evidence D
L-Taurine full monograph & interactions

L-Tyrosine2 drug types · 21 drugs

Levodopa

Theoretically, tyrosine might decrease the effectiveness of levodopa.
Tyrosine and levodopa compete for absorption in the proximal duodenum by the large neutral amino acid (LNAA) transport system. Advise patients to separate doses of tyrosine and levodopa by at least 2 hours.

Likelihood Probable Evidence D
Thyroid Hormone

Theoretically, tyrosine might have additive effects with thyroid hormone medications.
Tyrosine is a precursor to thyroxine and might increase levels of thyroid hormones.

Likelihood Probable Evidence D
L-Tyrosine full monograph & interactions

Vitamin B-121 drug type · 20 drugs

Metformin (Glucophage)

Metformin, a common medication used to manage type 2 diabetes, has been associated with lower vitamin B12 levels in some individuals. Prolonged use of metformin can interfere with the absorption of B12 in the digestive system, potentially leading to a deficiency in this essential vitamin.

Likelihood Possible Evidence A
Vitamin B-12 full monograph & interactions
The maker

Brand information

Manufacturer and brand details for 8 Hour Unflavored, from the product label.

Muscle Feast

See all Muscle Feast products
Name
Muscle Feast
Street Address
1320 Boston Road
City
Nashport
State
OH
ZipCode
43830
Phone Number
(888) 734-3634
Web Address
www.musclefeast.com
Pharmacist Counseling Corner

8 Hour Unflavored by Muscle Feast: Common Questions

Does 8 Hour Unflavored by Muscle Feast interact with any medications?
Yes. Based on its ingredients, 8 Hour Unflavored has a known interaction with 770 medications, including 8 rated major. Use the checker to see how it interacts with a specific drug.
How can one product interact with so many drugs?
8 Hour Unflavored contains 6 active ingredients, and an interaction can come from any of them. We check every ingredient, combine the results into one list per medication, and show which ingredient and mechanism is responsible.
Where does this information come from?
The product label data comes from the NIH Dietary Supplement Label Database (DSLD); the interaction data is built on the Natural Medicines database and reviewed by HelloPharmacist pharmacists.
Will this keep me awake at night?
It might. Caffeine commonly causes insomnia and sleep disturbances, especially in adults. If you're sensitive to caffeine or take this late in the day, that's a real risk. Start with a small dose and see how it affects your sleep.
Can I take this while I'm pregnant?
The data on caffeine in pregnancy is mixed—it's rated possibly safe and possibly unsafe. L-Taurine and Vitamin B-12 are likely safe in pregnancy, but L-Tyrosine and Vitamin B-6 don't have enough safety data. Talk to your doctor about safe caffeine limits and whether this product is right for you.
Can I take this while breastfeeding?
Small amounts of caffeine pass into breast milk and are usually considered acceptable, but they can affect the baby. L-Taurine and Vitamin B-12 are likely safe. L-Tyrosine and Vitamin B-6 don't have enough safety data on supplements during breastfeeding—ask your doctor or pharmacist.
What is L-Taurine for in this product?
L-Taurine is an amino acid that may support energy and athletic performance. It's possibly effective for liver and heart health in some studies, though it doesn't seem to help with weight loss.
What does L-Tyrosine do?
L-Tyrosine is an amino acid your body uses to make neurotransmitters and thyroid hormone. In this product it's possibly effective for memory and mental function, though the evidence for athletic performance is mixed.
Is this safe to use every day?
Caffeine at moderate doses is generally well tolerated daily, but high amounts can cause serious side effects and dependence. The other ingredients are generally well tolerated short-term, but long-term safety data is limited. If you're using it daily, talk to your pharmacist or doctor about safe limits for you.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

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Label information is sourced from the NIH Dietary Supplement Label Database and reflects the product version on file; always read your actual product label. This page is for education only and is not a substitute for professional medical advice. Confirm with your pharmacist or doctor before combining supplements and medications.

8 Hour Unflavored label
Go deeper

The Full Monographs Behind 8 Hour Unflavored’s Ingredients

Every ingredient we hold a full HelloPharmacist monograph for — uses, evidence, safety, and the complete interaction list.

Herb & supplement monograph

Caffeine

Interacts with 655 drugs

Caffeine is a natural stimulant found in coffee, tea, and many other plants and products. In moderate amounts it can boost alertness and reduce tiredness for most healthy adults, but too muc...

Read the full Caffeine monograph → Herb & supplement monograph

Taurine

Interacts with 173 drugs

Taurine is an amino acid your body makes naturally and that you also get from animal foods. It is widely used in energy drinks and sports supplements, and short-term use appears generally sa...

Read the full Taurine monograph → Herb & supplement monograph

Tyrosine

Interacts with 21 drugs

L-tyrosine is an amino acid your body uses to make brain chemicals like dopamine and norepinephrine. Some studies suggest it may help mental performance during short-term stress, sleep loss,...

Read the full Tyrosine monograph → Herb & supplement monograph

Vitamin B6

Interacts with 210 drugs

Vitamin B6 (pyridoxine) is an essential water-soluble vitamin that your body needs for metabolism, brain function, and making red blood cells. It is best known for helping with pregnancy-rel...

Read the full Vitamin B6 monograph → Herb & supplement monograph

Vitamin B12

Interacts with 20 drugs

Vitamin B12 (cobalamin) is an essential nutrient your body needs to make red blood cells, keep nerves healthy, and support DNA. Supplements are very helpful for people who are deficient — su...

Read the full Vitamin B12 monograph →
Sources

Sources & How We Checked

8 Hour Unflavored's label data comes from the NIH Dietary Supplement Label Database; the ingredient interaction data is from the Natural Medicines database, reviewed by our pharmacists.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

The 323 references behind this product’s interaction data

Every citation that drives the interaction findings for this product’s ingredients, from the evidence-graded Natural Medicines (TRC Healthcare) database. Open an ingredient to browse its citations — links open the study on PubMed or the publisher’s site.

Caffeine 236 references
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Tyrosine 4 references
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Vitamin B6 32 references
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Vitamin B12 30 references
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DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

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