Major interaction on record — check this product against your medications before combining. Based on 13 of 18 ingredients. Check your meds →
Dietary supplement

Free Form Amino Caps Ingredients & Drug Interactions

by Douglas Laboratories

Free Form Amino Caps label
See full label image
Capsule Category: Amino Acid/protein
Most serious interaction: Major
Clinical methodology reviewed by · Updated Sep 9, 2026 · Label data from the NIH DSLD
What is this page for?

First and foremost: checking Free Form Amino Caps 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

Free Form Amino Caps is a dietary supplement by Douglas Laboratories with 18 active ingredients. Its ingredients are commonly taken for high blood pressure, erectile dysfunction, athletic performance.Based on those ingredients, 439 medications have a known interaction with it, the most serious rated major. The ingredients most likely to interact are L-Arginine, L-Tyrosine, L-Phenylalanine. Use the checker below to test your specific medication, or read the full HelloPharmacist Interaction Report.

Jump to a section

Check Your Meds Against Free Form Amino Caps by Douglas Laboratories

Ask about any prescription or over-the-counter medication and we check it for interactions with Free Form Amino Caps by Douglas Laboratories — and tell you which ingredient is responsible.

Pharmacist-reviewed data Checks every ingredient Answer in seconds
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HelloPharmacist Scorecard of Free Form Amino Caps by Douglas Laboratories

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 30, 2026

What’s inside

Low disclosure
Ingredient Transparency · database check
Low

Most active ingredients don't disclose an individual amount — you can't tell how much of each you're getting.

Why this rating?
  • The label discloses an exact amount for 0 of its 18 active ingredients.
  • “Free Form Amino Acids Proprietary Blend” is a proprietary blend — the label gives one combined amount (600 mg) without saying how much of each component you get.

Free Form Amino Caps contains 18 amino acid ingredients — the building blocks your body uses to make proteins and neurotransmitters. The active amino acids include L-leucine, L-arginine, L-alanine, L-isoleucine, L-methionine, L-tyrosine, L-phenylalanine, L-valine, L-proline, L-glycine, L-aspartic acid, L-histidine, L-glutamic acid, L-threonine, L-ornithine, L-lysine, L-serine, and L-cystine.

The capsules also contain inactive ingredients (gelatin, silica, magnesium silicate, and stearate) that serve as fillers and binders.

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

This product doesn't appear to be marketed for a specific use, so we graded its ingredients' overall clinical evidence instead.

Strong

Strong clinical evidence supports its ingredients for:

Why this rating?
  • We looked at the product name, claims, and label statements and couldn't find a stated purpose to grade.
  • Since the label doesn't commit to one use, we graded the ingredients' overall clinical evidence instead.
  • On file: Phenylketonuria (PKU) — rated "Effective" (Tyrosine) (Natural Medicines).
  • On file: Neural tube birth defects — rated "Possibly Effective" (Methionine) (Natural Medicines).
  • On file: Athletic performance — rated "Possibly Effective" (Ornithine) (Natural Medicines).
  • On file: Herpes labialis (cold sores) — rated "Possibly Effective" (Lysine) (Natural Medicines).
  • On file: Cholera — rated "Possibly Effective" (Histidine) (Natural Medicines).

The evidence for most amino acids in this blend is not well established in the data we hold. L-tyrosine shows possibly effective evidence for cognitive function and memory, and L-phenylalanine shows possibly effective evidence for vitiligo.

L-lysine is possibly effective for cold sores. L-ornithine shows possibly effective evidence for athletic performance.

Beyond those, the remaining ingredients either show insufficient evidence or we lack effectiveness ratings altogether.

The evidence, ingredient by ingredient L-arginine Alpha-alanine Methionine Tyrosine Phenylalanine Proline Glycine Aspartic Acid

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 8 of the 13 matched ingredients.
  • Pregnancy & breastfeeding safety ratings cover 13 of 13.
  • General safety write-ups exist for 13 of 13.
  • Remember: this measures how much safety information exists. Thin data is not the same as being safe.

Most of these amino acids are generally well tolerated in short-term use from food sources. L-arginine can lower blood pressure and requires medical supervision — it's not safe for self-treatment without guidance.

L-phenylalanine should be avoided by anyone with phenylketonuria (PKU). Adverse effects reported across the ingredients include gastrointestinal symptoms (nausea, diarrhea, abdominal pain, bloating), headache, fatigue, heartburn, and insomnia.

Long-term safety data for most supplement doses are limited, and some amino acids (L-serine, L-aspartic acid) have not been well studied in pregnancy or while breastfeeding.

Side effects, ingredient by ingredient L-arginine Alpha-alanine Methionine Tyrosine Phenylalanine Proline Glycine Aspartic Acid

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?
  • 6 of the 13 matched ingredients can interact with medications — Lysine, Phenylalanine, L-arginine, Tyrosine, Glycine, among others.
  • The most serious interaction on file is rated Major.
  • Some involve high-stakes drug classes: anticoagulant / antiplatelet drugs; diabetes medications; Parkinson's medications.
  • For scale: 439 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 Free Form Amino Caps, double-check with your doctor or pharmacist if you take any of these: levodopa (Major severity), blood pressure medications including ACE inhibitors and ARBs (Moderate), blood thinners or antiplatelet drugs (Moderate), diabetes medications (Moderate), potassium-sparing diuretics (Moderate), baclofen (Moderate), monoamine oxidase inhibitors or MAOIs (Moderate), isoproterenol (Moderate), sildenafil/Viagra (Moderate), NMDA antagonists (Major), clozapine (Moderate), or 5-HT4 agonists (Minor). No interactions are documented for L-leucine, L-isoleucine, L-valine, and L-glutamic acid, which we could not fully check.

Check your own medication Run your meds through the checker above

The bottom line

Scorecard at a glanceFormula with limited ingredient disclosure with strong clinical evidence behind its ingredients' uses. Major medication interactions have been identified, and safety information is well characterized.

This product is a blend of amino acids that may appeal to people looking to support protein synthesis or neurological function, but the evidence for most ingredients is thin. If you take levodopa (for Parkinson's), blood pressure medications, blood thinners, diabetes drugs, or psychiatric medications like clozapine, you need to check with your doctor or pharmacist before adding this product — interactions are documented and could affect how your medications work.

Talk it over with your healthcare provider to see if this product is right for you.

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

Assessment coverage: 13 of 18 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 Free Form Amino Caps, straight from the product label.

Brand Douglas Laboratories
Barcode (UPC) 310539820056
Net contents 100 Capsule(s)
Market status On market
Date entered into DSLD Feb 23, 2022
DSLD ID 261115
Product type Amino Acid/protein
Supplement form Capsule
Dietary claims / uses Nutrient, All Other, Structure/Function
Intended target group(s) Adult (18 - 50 Years), 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 Free Form Amino Caps by Douglas Laboratories, 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 Capsule(s)
Maximum serving Sizes:
1 Capsule(s)
Servings per container
100
UPC/BARCODE
310539820056
IngredientAmount% DV
L-Leucine0 NP--
L-Arginine0 NP--
L-Alanine0 NP--
L-Isoleucine0 NP--
L-Methionine0 NP--
L-Tyrosine0 NP--
L-Phenylalanine0 NP--
L-Valine0 NP--
L-Proline0 NP--
L-Glycine0 NP--
L-Aspartic Acid0 NP--
L-Histidine0 NP--
L-Glutamic Acid0 NP--
L-Threonine0 NP--
L-Ornithine0 NP--
L-Lysine0 NP--
L-Serine0 NP--
L-Cystine0 NP--
Free Form Amino Acids Proprietary Blend600 mg--

Other ingredients: Gelatin, Silica, Magnesium Silicate, Stearate

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.
Suggested/Recommended/Usage/Directions

Suggested Usage: As a dietary supplement, adults take 1 capsule daily or as directed by your health professional.

Precautions

Warning: If you are pregnant, nursing, have any health condition or taking any medication, consult your health professional before using this product.

Phenylketonurics: Contains phenylalanine.

Keep out of the reach of children.

Use only if safety seal is intact.

Storage

Store in a cool, dry place.

Formulation

Gluten-free, Non-GMO

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.

General Statements

Scan to learn about our manufacturing excellence Contents may not fill package in order to accommodate required labeling. Please rely on stated quantity.

FDA Statement of Identity

Dietary Supplement

Formula

Nutritionally balanced amino acids

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

See for yourself

Free Form Amino Caps by Douglas Laboratories label

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

Free Form Amino Caps 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 Free Form Amino Caps by Douglas Laboratories

These are the 18 active ingredients this product is made of. Select any to open its full monograph.

Serving size1 Capsule(s) Dosage formCapsule Servings per container100 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.

Free Form Amino Acids Proprietary Blend

600 mg per serving

Other (inactive) ingredients: Gelatin, Silica, Magnesium Silicate, Stearate. These complete the product’s ingredient list but are not active constituents.

Interaction report

Free Form Amino Caps by Douglas Laboratories Drug Interactions

Want to check YOUR meds against Free Form Amino Caps?

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
439Drugs
8 Major 423 Moderate 8 Minor

Ingredients driving the most interactions

L-Arginine 403
L-Tyrosine 21
L-Phenylalanine 16
L-Threonine 3
L-Glycine 1

Individual Drug Interactions

The ingredients in Free Form Amino Caps interact with 439 drugs. Click any drug to see the details.

6 of the 18 ingredients in Free Form Amino Caps interact with drugs. Each result below shows which ingredient is responsible. L-Arginine L-Tyrosine L-Phenylalanine L-Threonine L-Glycine L-Lysine

Each ingredient & the kinds of drugs it affects

For each ingredient in Free Form Amino Caps 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.

L-Arginine9 drug types · 403 drugs

Ace Inhibitors (Aceis)

Theoretically, concomitant use of L-arginine and ACE inhibitors may increase the risk for hypotension and hyperkalemia.
Combining L-arginine with some antihypertensive drugs, especially ACE inhibitors, seems to have additive vasodilating and blood pressure-lowering effects. Furthermore, ACE inhibitors can increase potassium levels. Use of L-arginine has been associated with hyperkalemia in some patients. Theoretically, concomitant use of ACE inhibitors with L-arginine may increases the risk of hyperkalemia.

Likelihood Probable Evidence D
Angiotensin Receptor Blockers (Arbs)

Theoretically, concomitant use of L-arginine and ARBs may increase the risk of hypotension and hyperkalemia.
L-arginine increases nitric oxide, which causes vasodilation. Combining L-arginine with ARBs seems to increase L-arginine-induced vasodilation. Furthermore, ARBs can increase potassium levels. Use of L-arginine has been associated with hyperkalemia in some patients. Theoretically, concomitant use of ARBs with L-arginine may increases the risk of hyperkalemia.

Likelihood Probable Evidence D
Anticoagulant/Antiplatelet Drugs

Theoretically, concomitant use of L-arginine with anticoagulant and antiplatelet drugs might have additive effects and increase the risk of bleeding.
Preliminary research suggests that L-arginine infusions reduce platelet aggregation in humans. The clinical significance of this effect is unclear.

Likelihood Possible Evidence D
Antidiabetes Drugs

Theoretically, concomitant use of L-arginine might have additive effects with antidiabetes drugs.
Preliminary clinical research shows that L-arginine decreases blood glucose levels in patients with type 2 diabetes.

Likelihood Possible Evidence D
Antihypertensive Drugs

Theoretically, concomitant use of L-arginine and antihypertensive drugs may increase the risk of hypotension.
L-arginine increases nitric oxide, which causes vasodilation. Clinical evidence shows that L-arginine can reduce blood pressure in some individuals with hypertension. Furthermore, combining L-arginine with some antihypertensive drugs seems to have additive vasodilating and blood pressure-lowering effects.

Likelihood Probable Evidence D
Isoproterenol (Isuprel)

Theoretically, concurrent use of isoproterenol and L-arginine might result in additive effects and hypotension.
Preliminary clinical evidence suggests that L-arginine enhances isoproterenol-induced vasodilation in patients with essential hypertension or a family history of essential hypertension.

Likelihood Probable Evidence D
Potassium-Sparing Diuretics

Theoretically concomitant use of potassium-sparing diuretics with L-arginine may increases the risk of hyperkalemia.
Potassium-sparing diuretics can increase potassium levels. Use of L-arginine has been associated with hyperkalemia in some patients.

Likelihood Possible Evidence D
Sildenafil (Viagra)

Theoretically, concurrent use of sildenafil and L-arginine might increase the risk for hypotension.
In vivo, concurrent use of L-arginine and sildenafil has resulted in increased vasodilation. Theoretically, concurrent use might have additive vasodilatory and hypotensive effects. However, in studies evaluating the combined use of L-arginine and sildenafil for erectile dysfunction, hypotension was not reported.

Likelihood Possible Evidence D
Testosterone

Theoretically, concomitant use of L-arginine and testosterone might have additive effects.
In clinical research, L-arginine increases the level of testosterone in male patients with erectile dysfunction. The clinical significance of this finding is unclear.

Likelihood Possible Evidence D
L-Arginine 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

L-Phenylalanine3 drug types · 16 drugs

Levodopa

Phenylalanine, especially in high doses, can reduce the effectiveness of levodopa.
Phenylalanine competes with levodopa for carrier-mediated transport into the brain. The resulting reduction in levels of levodopa in the brain can exacerbate tremor, rigidity, and the "on-off" phenomenon in patients with Parkinson disease.

Likelihood Probable Evidence B
Baclofen

Concomitant intake of phenylalanine may reduce the intestinal absorption of baclofen.
Phenylalanine and baclofen share the same intestinal carrier for absorption; phenylalanine competitively inhibits the absorption of baclofen, reducing its plasma levels.

Likelihood Possible Evidence D
Monoamine Oxidase Inhibitors (Maois)

Theoretically, concomitant use of L-phenylalanine and non-selective MAOIs might increase the risk of hypertensive crisis.
L-phenylalanine is metabolized to tyrosine. Some evidence suggests that L-phenylalanine, given with the non-selective MAOI pargyline, might prevent the elimination of tyramine, increasing the risk of hypertensive crisis. However, this was not reported in a small number of patients when using L-phenylalanine with the partially selective MAO-B inhibitor, selegiline.

Likelihood Possible Evidence D
L-Phenylalanine full monograph & interactions

L-Threonine1 drug type · 3 drugs

Nmda Antagonists

Theoretically, threonine might decrease the effects of NMDA antagonists.
Threonine increases central nervous system (CNS) glycine levels. Glycine seems to bind a site on NMDA receptors and enhance the activity of the receptors.

Likelihood Likely Evidence B
L-Threonine full monograph & interactions

L-Glycine1 drug type · 1 drug

Clozapine (Clozaril)

Theoretically, glycine might decrease the effectiveness of clozapine.
One small clinical study in patients with schizophrenia shows that adding glycine to clozapine therapy worsens symptoms of schizophrenia when compared with clozapine alone. The mechanism of this interaction is unclear.

Likelihood Probable Evidence B
L-Glycine full monograph & interactions

L-Lysine1 drug type · 1 drug

5-Ht4 Agonists

Theoretically, lysine may reduce the effects of 5-HT4 agonists.
Animal research suggests that L-lysine is a partial serotonin receptor 4 (5-HT4) antagonist and inhibits diarrhea induced by the 5-HT4 agonist, 5-hydroxytryptophane.

Likelihood Unlikely Evidence D
L-Lysine full monograph & interactions
The maker

Brand information

Manufacturer and brand details for Free Form Amino Caps, from the product label.

Douglas Laboratories

See all Douglas Laboratories products
Name
Douglas Laboratories
Street Address
600 Boyce Road
City
Pittsburgh
State
PA
ZipCode
15205
Phone Number
1.800.245.4440
Web Address
www.douglaslabs.com
Pharmacist Counseling Corner

Free Form Amino Caps by Douglas Laboratories: Common Questions

Does Free Form Amino Caps by Douglas Laboratories interact with any medications?
Yes. Based on its ingredients, Free Form Amino Caps has a known interaction with 439 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?
Free Form Amino Caps contains 18 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.
Is this product safe to take while pregnant or breastfeeding?
Safety data vary by ingredient. L-arginine is possibly safe in pregnancy, L-phenylalanine is rated unsafe during pregnancy, and L-methionine, L-proline, and L-ornithine don't have enough data. Several ingredients (L-alanine, L-methionine) are likely safe while breastfeeding, but others lack studied safety. Because this is a multi-ingredient blend with mixed safety ratings, talk with your doctor or pharmacist before use if you're pregnant or nursing.
What are the most common side effects?
Gastrointestinal symptoms are most reported — abdominal pain, bloating, nausea, and diarrhea. You may also experience headache, fatigue, heartburn, or insomnia. Most side effects are mild and go away when you stop taking the product, but if they persist or worsen, stop and contact your healthcare provider.
Does this product actually work?
Evidence is limited for most ingredients. L-tyrosine has possibly effective evidence for cognitive function and memory, L-lysine for cold sores, and L-ornithine for athletic performance. The rest either lack solid evidence or we don't have effectiveness data on file. If you're taking it for a specific condition, ask your doctor whether the science supports that use.
Can I take this if I have Parkinson's disease or take levodopa?
No — both L-phenylalanine (Major severity) and L-tyrosine (Moderate severity) interfere with levodopa absorption in the brain and can reduce its effectiveness. Talk with your doctor or pharmacist; you may need to skip this product or take it at a very different time from your medication.
What is L-arginine in this product?
L-arginine is an amino acid that your body uses to make nitric oxide, which relaxes blood vessels and lowers blood pressure. It has several documented interactions with blood pressure drugs, blood thinners, and diabetes medications, so it requires caution if you take those. Always check with your doctor or pharmacist first.
Is there anyone who should definitely avoid this product?
Yes — anyone with PKU (phenylketonuria) should avoid it because of the L-phenylalanine content. Anyone taking levodopa, blood pressure medications, blood thinners, diabetes drugs, or clozapine should talk with their doctor or pharmacist first. L-arginine also requires medical supervision and is not recommended for self-treatment.

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

Not sure if Free Form Amino Caps is safe with your meds?

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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.

Free Form Amino Caps label
Go deeper

The Full Monographs Behind Free Form Amino Caps’s Ingredients

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

Herb & supplement monograph

L-arginine

Interacts with 403 drugs

L-arginine is an amino acid that the body uses to make nitric oxide, a substance that helps blood vessels relax and widen. It is popularly used for blood pressure, erectile dysfunction, and...

Read the full L-arginine monograph → Herb & supplement monograph

Alpha-alanine

Alpha-alanine (usually called alanine) is a non-essential amino acid your body can make on its own and that you also get from protein foods. Most people do not need a supplement, and strong...

Read the full Alpha-alanine monograph → Herb & supplement monograph

Methionine

Methionine is an essential amino acid that your body needs for protein building and many basic chemical reactions. Most people get enough from a normal diet, and supplements are generally no...

Read the full Methionine 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

Phenylalanine

Interacts with 16 drugs

Phenylalanine is an essential amino acid the body uses to make brain chemicals like dopamine and norepinephrine. Some people take it for mood, vitiligo, or pain, but the evidence is mostly l...

Read the full Phenylalanine monograph → Herb & supplement monograph

Proline

Proline is a non-essential amino acid that your body can make on its own and that you also get from protein-rich foods. It is a key building block of collagen, but strong human evidence that...

Read the full Proline monograph → Herb & supplement monograph

Glycine

Interacts with 1 drug

Glycine is a non-essential amino acid your body makes on its own and that also appears in protein-rich foods. It is most studied for improving sleep quality, where early research is promisin...

Read the full Glycine monograph → Herb & supplement monograph

Aspartic Acid

Aspartic acid is a common amino acid your body makes on its own and gets from protein-rich foods, so a true deficiency is rare. D-aspartic acid is heavily marketed for boosting testosterone...

Read the full Aspartic Acid monograph → Herb & supplement monograph

Histidine

Histidine is an essential amino acid your body needs to build proteins and to make compounds like histamine and carnosine. Most people get enough from a normal diet, and good-quality researc...

Read the full Histidine monograph → Herb & supplement monograph

Threonine

Interacts with 3 drugs

Threonine is an essential amino acid your body needs but cannot make, so you must get it from food or supplements. Most people get plenty from a normal diet, and high-quality evidence for ta...

Read the full Threonine monograph → Herb & supplement monograph

Ornithine

Ornithine is a non-essential amino acid your body makes naturally as part of the urea cycle, which helps remove ammonia. It is sold as a supplement for fatigue, exercise recovery, and sleep,...

Read the full Ornithine monograph → Herb & supplement monograph

Lysine

Interacts with 1 drug

Lysine is an essential amino acid your body cannot make on its own, so it must come from food or supplements. People most often take extra lysine to try to prevent or shorten cold sores, but...

Read the full Lysine monograph → Herb & supplement monograph

Serine

Serine is an amino acid your body can make on its own and also gets from protein-rich foods, so most people do not need a supplement. L-serine has been studied for certain neurological condi...

Read the full Serine monograph →
Sources

Sources & How We Checked

Free Form Amino Caps'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 135 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.

L-arginine 66 references
  1. Sapienza MA, Kharitonov SA, Horvath I, et al. Effect of inhaled L-arginine on exhaled nitric oxide in normal and asthmatic subjects. Thorax 1998;53:172-5.
  2. Clarkson P, Adams MR, Powe AJ, et al. Oral L-arginine improves endothelium-dependent dilation in hypercholesterolemic young adults. J Clin Invest 1996;97:1989-94. PubMed
  3. Tenenbaum A, Fisman EZ, Motro M. L-arginine: Rediscovery in progress. Cardiology 1998;90:153-9.
  4. Brittenden J, Park KGM, Heys SD, et al. L-Arginine stimulates host defenses in patients with breast cancer. Surgery 1994;115:205-12.
  5. Korting GE, Smith SD, Wheeler MA, et al. A randomized double-blind trial of oral L-arginine for treatment of interstitial cystitis. J Urol 1999;161:558-65. DOI
  6. Rector TS, Bank AJ, Mullen KA, et al. Randomized, double-blind, placebo-controlled study of supplemental oral L-arginine in patients with heart failure. Circulation 1996;93:2135-41.
  7. Siani A, Pagano E, Iacone R, et al. Blood pressure and metabolic changes during dietary L-arginine supplementation in humans. Am J Hypertens 2000;13:547-51. PubMed
  8. Cheng JW, Balwin SN. L-arginine in the management of cardiovascular diseases. Ann Pharmacother 2001;35:755-64. PubMed
  9. Wallace AW, Tom WL. Interaction of L-arginine and phosphodiesterase inhibitors in vasodilation of the porcine internal mammary artery. Anesth Analg 2000;90:840-6. DOI
  10. Huynh NT, Tayek JA. Oral arginine reduces systemic blood pressure in type 2 diabetes: its potential role in nitric oxide generation. J Am Coll Nutr 2002;21:422-7.. PubMed
  11. Staff AC, Berge L, Haugen G, et al. Dietary supplementation with L-arginine or placebo in women with pre-eclampsia. Acta Obstet Gynecol Scand 2004;83:103-7.
  12. Resnick DJ, Softness B, Murphy AR, et al. Case report of an anaphylactoid reaction to arginine. Ann Allergy Asthma Immunol 2002;88:67-8. PubMed
  13. Anon. Arginine hydrochloride injection (marketed as R-Gene 10). FDA Drug Safety Newsletter 2009;2(2):16-18. Available at: www.fda.gov/Drugs/DrugSafety/DrugSafetyNewsletter/default.htm.
  14. Higashi Y, Oshima T, Sasaki S, et. al. Angiotensin-converting enzyme inhibition, but not calcium antagonism, improves a response of the renal vasculature to L-arginine in patients with essential hypertension. Hypertension. 1998 Jul;32(1):16-24.
  15. Facchinetti, F., Longo, M., Piccinini, F., Neri, I., and Volpe, A. L-arginine infusion reduces blood pressure in preeclamptic women through nitric oxide release. J Soc Gynecol.Investig. 1999;6(4):202-207. DOI
  16. de Gouw, H. W., Verbruggen, M. B., Twiss, I. M., and Sterk, P. J. Effect of oral L-arginine on airway hyperresponsiveness to histamine in asthma. Thorax 1999;54(11):1033-1035. PubMed
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Alpha-alanine 2 references
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See these in context on the Alpha-alanine monograph →

Methionine 12 references
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Tyrosine 4 references
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Phenylalanine 23 references
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Proline 4 references
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Glycine 5 references
  1. Heresco-Levy U, Javitt DC, Ermilov M, et al. Efficacy of high-dose glycine in the treatment of enduring negative symptoms of schizophrenia. Arch Gen Psychiatry 1999;56:29-36.. PubMed
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Aspartic Acid 1 reference
  1. Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington, DC: The National Academies Press, 2005. Available at: https://doi.org/10.17226 DOI

See these in context on the Aspartic Acid monograph →

Histidine 3 references
  1. Histidine — MedlinePlus (U.S. National Library of Medicine) Source
  2. Amino Acids — MedlinePlus (U.S. National Library of Medicine) Source
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See these in context on the Histidine monograph →

Threonine 4 references
  1. Tandan R, Bromberg MB, Forshew D, et al. A controlled trial of amino acid therapy in amyotrophic lateral sclerosis: I. Clinical, functional, and maximum isometric torque data. Neurology 1996;47:1220-6. PubMed
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Ornithine 1 reference
  1. Dietary Supplements: What You Need to Know — NIH Office of Dietary Supplements Source

See these in context on the Ornithine monograph →

Lysine 7 references
  1. Thein DJ, Hurt WC. Lysine as a prophylactic agent in the treatment of recurrent herpes simplex labialis. Oral Surg Oral Med Oral Pathol 1984;58:659-66. PubMed
  2. McCune MA, Perry HO, Muller SA, O'Fallon WM. Treatment of recurrent herpes simplex infections with L-lysine monohydrochloride. Cutis 1984;34:366-73.
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See these in context on the Lysine monograph →

Serine 3 references
  1. Fridman V, Suriyanarayanan S, Novak P, et al. Randomized trial of l-serine in patients with hereditary sensory and autonomic neuropathy type 1. Neurology. 2019;92(4):e359-e370.
  2. Kantrowitz JT, Malhotra AK, Cornblatt B, et al. High dose D-serine in the treatment of schizophrenia. Schizophr Res. 2010 Aug;121(1-3):125-30. PubMed
  3. Levine TD, Miller RG, Bradley WG, et al. Phase I clinical trial of safety of L-serine for ALS patients. Amyotroph Lateral Scler Frontotemporal Degener. 2017;18(1-2):107-111. PubMed

See these in context on the Serine monograph →

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