FLEX Ingredients & Drug Interactions
by AdvoCare
What is this page for?
First and foremost: checking FLEX 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
FLEX is a dietary supplement by AdvoCare with 8 active ingredients. Its ingredients are commonly taken for acetaminophen (tylenol) overdose support, liver health, urinary tract acidification.Based on those ingredients, 4 medications have a known interaction with it, the most serious rated major. The ingredients most likely to interact are L-Threonine, L-Glycine. Use the checker below to test your specific medication, or read the full HelloPharmacist Interaction Report.
Check Your Meds Against FLEX by AdvoCare
Ask about any prescription or over-the-counter medication and we check it for interactions with FLEX by AdvoCare — and tell you which ingredient is responsible.
AI summaries are generated from our interaction database for education only — always confirm with your pharmacist. How we use AI
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HelloPharmacist Scorecard of FLEX by AdvoCare
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.
What’s inside
Partial disclosure
FLEX contains 8 active ingredients, all amino acids and collagen forms. The amino acids are L-methionine, L-proline, L-glycine, L-histidine, L-threonine, L-serine, and the product also includes undenatured Type II Collagen and Total Collagen, along with UC-II standardized Cartilage.
These are the building blocks your body uses to form and repair connective tissue — primarily to support joints and overall flexibility. The capsules also contain inactive ingredients including microcrystalline cellulose (a binder), gelatin (the capsule shell), and L-leucine.
Does it work?
Not established
The evidence we have is limited and mixed. L-methionine is rated possibly effective for neural tube birth defects, and L-serine and L-glycine are each rated possibly effective for schizophrenia — but this product is marketed for joint health, not these conditions.
For the joint-related purposes most people buy this for — like osteoporosis, fractures, and wound healing — the evidence we hold rates as insufficient to know whether these ingredients work. That doesn't mean they don't; it means the data to prove it isn't established yet in what we have on file.
How safe is it?
Well-documented data
L-methionine, L-proline, L-histidine, L-threonine, and L-glycine are generally well tolerated at typical doses, though long-term safety data are limited for some. Common side effects reported are mild and infrequent — dizziness, drowsiness, headache, and gastrointestinal upset (nausea, bloating, diarrhea) resolve quickly if they occur.
For pregnancy and breastfeeding: L-methionine and L-histidine are rated likely safe; L-proline, L-glycine, L-threonine, and L-serine don't have enough reliable safety data on supplement doses, so talk with your doctor or pharmacist for personalized advice before using this product if you're pregnant or breastfeeding.
Meds to double-check
Major interaction found
Before you take FLEX, double-check if you're on any NMDA antagonists (memantine and similar drugs for dementia or other conditions) — L-threonine may lower how well they work, and this is a Major concern. Also check if you take clozapine (Clozaril) for schizophrenia; L-glycine could worsen symptoms.
Your pharmacist or doctor can confirm whether any of your medications fall into these categories.
The bottom line
Scorecard at a glancePartially disclosed formula with no established evidence rating for its marketed use. Major medication interactions have been identified, and safety information is well characterized.
FLEX is a blend of amino acids and collagen meant to support joint flexibility and connective tissue health. If you take an NMDA antagonist or clozapine, check with your doctor or pharmacist before starting this product — it may affect how well your medication works.
Otherwise, it's generally well tolerated, though evidence for its effectiveness isn't established in the data we hold. Talk it over with your own doctor or pharmacist to see if it's right for your situation.
Educational only — not medical advice; always confirm with your pharmacist. Our editorial policy · How we use AI
Assessment coverage: 6 of 8 active ingredients matched to our full ingredient reviews (monographs). Based on the product label dated May 19, 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
General information
Key facts about FLEX, straight from the product label.
| Brand | AdvoCare |
|---|---|
| Net contents | 60 Capsule(s) |
| Market status | On market |
| Date entered into DSLD | May 19, 2022 |
| DSLD ID | 265365 |
| Product type | Other Combinations |
| Supplement form | Capsule |
| Dietary claims / uses | All Other, Structure/Function |
| Intended target group(s) | Adult (18 - 50 Years) |
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 FLEX by AdvoCare, sourced from the NIH Dietary Supplement Label Database.
Supplement Facts
| Ingredient | Amount | % DV |
|---|---|---|
| L-Methionine | 100 mg | -- |
| L-Proline | 400 mg | -- |
| L-Glycine | 100 mg | -- |
| L-Histidine | 100 mg | -- |
| L-Threonine | 100 mg | -- |
| undenatured Type II Collagen | 0 NP | -- |
| L-Serine | 100 mg | -- |
| Total Collagen | 10 mg | -- |
| UC-II standardized Cartilage | 40 mg | -- |
Other ingredients: Microcrystalline Cellulose, Gelatin, L-Leucine
Tap any ingredient to jump to its full detail below.
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.
General Statements
For more information visit advocare.com
Suggested/Recommended/Usage/Directions
Directions For Use: Take 2 capsules, once per day on an empty stomach.
Precautions
Note: Check with your healthcare professional before using this product.
Keep out of reach of children.
Storage
Store away from excessive heat, light and humidity.
Brand IP Statement(s)
UC-II is a registered trademark of Interhealth N.I. UC-II brand collagen with undenatured type II collagen (U.S. Patents 7,083,820, 7,846,487, and EPO Patent EP 1435906B1; Canadian Patent CA 2459981C; and Japanese Patent JP 4800574B2)
FDA Disclaimer Statement
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.
FDA Statement of Identity
Amino Acid and Collagen Supplement
Formulation
Supports joint health, mobility and flexibility Contributes to the body's natural production of collagen and supports healthy connective tissue
Seals/Symbols
Informed Sport We Test-You Trust
Is this label outdated? Report a formula or label change and our pharmacy team will review it.
FLEX by AdvoCare label
The label scan from the NIH Dietary Supplement Label Database. Tap to enlarge.
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)The Ingredients in FLEX by AdvoCare
These are the 8 active ingredients this product is made of. Select any to open its full monograph.
Serving size2 Capsule(s) Dosage formCapsule Servings per container30 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.
L-Methionine
No knowninteractions
Methionine is an essential amino acid that your body needs for protein building and many basic chemical reactions. Most people get enough from a norma...
L-Methionine monograph & interactionsL-Proline
No knowninteractions
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...
L-Proline monograph & interactionsL-Glycine
Interacts with1 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 q...
L-Glycine monograph & interactionsL-Histidine
No knowninteractions
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...
L-Histidine monograph & interactionsL-Threonine
Interacts with3 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 norma...
L-Threonine monograph & interactionsL-Serine
No knowninteractions
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 bee...
L-Serine monograph & interactionsUC-II standardized Cartilage
- › Undenatured Type II Collagen
- › Total Collagen
Other (inactive) ingredients: Microcrystalline Cellulose, Gelatin, L-Leucine. These complete the product’s ingredient list but are not active constituents.
FLEX by AdvoCare Drug Interactions
HelloPharmacist Interaction Report
AdvoCare FLEX contains ingredients that do interact with a small number of medications: through its L-glycine and L-threonine content.
The most serious interaction is L-threonine with NMDA antagonists (a class of medications that block certain brain receptors), where threonine may reduce how well these drugs work — this is a Major severity concern. L-glycine carries a Moderate interaction with clozapine (Clozaril), an antipsychotic medication, where adding glycine may worsen schizophrenia symptoms.
Read the full breakdown — every affected drug type, severity by severity
Altogether, these interactions span 4 individual medications.
The other active ingredients we checked — L-methionine, L-proline, L-histidine, and L-serine — show no interactions documented in our data. We could not check undenatured Type II Collagen and Total Collagen because we don't hold interaction data for those ingredients.
If you take any prescription medication, especially an NMDA antagonist or clozapine, run it through our medication checker below before you start this product.
Check your own medications below · Editorial policy · How we use AI
Want to check YOUR meds against FLEX?
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 checkerIngredients driving the most interactions
Individual Drug Interactions
The ingredients in FLEX interact with 4 drugs. Click any drug to see the details.
2 of the 8 ingredients in FLEX interact with drugs. Each result below shows which ingredient is responsible. L-Threonine L-Glycine
MemantineEbixa
How Memantine interacts with FLEX — through 1 ingredient. Tap an ingredient for the detail:
L-threonineNmda Antagonists Major
Interaction Summary
Theoretically, threonine might decrease the effects of NMDA antagonists.
Read the full L-threonine + Memantine interactionMemantine HydrochlorideNamenda
How Memantine Hydrochloride interacts with FLEX — through 1 ingredient. Tap an ingredient for the detail:
L-threonineNmda Antagonists Major
Interaction Summary
Theoretically, threonine might decrease the effects of NMDA antagonists.
Read the full L-threonine + Memantine Hydrochloride interactionMemantine, DonepezilNamzaric
How Memantine, Donepezil interacts with FLEX — through 1 ingredient. Tap an ingredient for the detail:
L-threonineNmda Antagonists Major
Interaction Summary
Theoretically, threonine might decrease the effects of NMDA antagonists.
Read the full L-threonine + Memantine, Donepezil interactionClozapineClozaril, Versacloz
How Clozapine interacts with FLEX — through 1 ingredient. Tap an ingredient for the detail:
L-glycineClozapine (clozaril) Moderate
Interaction Summary
Theoretically, glycine might decrease the effectiveness of clozapine.
Read the full L-glycine + Clozapine interactionEach ingredient & the kinds of drugs it affects
For each ingredient in FLEX 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-Threonine
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.
L-Glycine
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.
Brand information
Manufacturer and brand details for FLEX, from the product label.
AdvoCare
- Name
- AdvoCare International, LLC
- City
- Richardson
- State
- TX
- ZipCode
- 75082
- Phone Number
- 800-542-4800
- Web Address
- advocare.com
FLEX by AdvoCare: Common Questions
Does FLEX by AdvoCare interact with any medications?
How can one product interact with so many drugs?
Where does this information come from?
Can I take FLEX if I'm pregnant?
Can I take FLEX while breastfeeding?
What side effects might I get from FLEX?
How do the amino acids in FLEX help joints?
Is there enough evidence that FLEX actually works for flexibility?
Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy
Not sure if FLEX is safe with your meds?
Our pharmacists answer your medication & supplement questions — free.
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.
The Full Monographs Behind FLEX’s Ingredients
Every ingredient we hold a full HelloPharmacist monograph for — uses, evidence, safety, and the complete interaction list.
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 monographProline
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 monographGlycine
Interacts with 1 drugGlycine 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 monographHistidine
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 monographThreonine
Interacts with 3 drugsThreonine 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 monographSerine
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 & How We Checked
FLEX'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.
- NIH Dietary Supplement Label Database (DSLD) — The official product label on file for this supplement.
- Natural Medicines (Therapeutic Research Center) — Evidence-graded clinical reference behind the ingredient interaction data.
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 31 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.
Methionine 12 references
- La Vecchia C, Negri E, Franceschi S, Decarli A. Case-control study on influence of methionine, nitrite, and salt on gastric carcinogenesis in northern Italy. Nutr Cancer 1997;27:65-8. PubMed
- Btaiche IF, Khalidi N. Parenteral nutrition-associated liver complications in children. Pharmacotherapy 2002;22:188-211.. PubMed
- Cottington EM, LaMantia C, Stabler SP, et al. Adverse event associated with methionine loading test: a case report. Arterioscler Thromb Vasc Biol 2002;22:1046-50.. PubMed
- Anon. Should methionine be added to paracetamol formulations? Drug Ther Perspect 1997;10:11-3. DOI
- Smulders, Y. M., Rakic, M., Slaats, E. H., Treskes, M., Sijbrands, E. J., Odekerken, D. A., Stehouwer, C. D., and Silberbusch, J. Fasting and post-methionine homocysteine levels in NIDDM. Determinants and correlations with retinopathy, albuminuria, and c
- McAuley, D. F., Hanratty, C. G., McGurk, C., Nugent, A. G., and Johnston, G. D. Effect of methionine supplementation on endothelial function, plasma homocysteine, and lipid peroxidation. J.Toxicol.Clin.Toxicol. 1999;37(4):435-440. PubMed
- Hanratty, C. G., McGrath, L. T., McAuley, D. F., Young, I. S., and Johnston, G. D. The effects of oral methionine and homocysteine on endothelial function. Heart 2001;85(3):326-330. PubMed
- Ward, M., McNulty, H., McPartlin, J., Strain, J. J., Weir, D. G., and Scott, J. M. Effect of supplemental methionine on plasma homocysteine concentrations in healthy men: a preliminary study. Int.J.Vitam.Nutr.Res. 2001;71(1):82-86. PubMed
- Yaghmai, R., Kashani, A. H., Geraghty, M. T., Okoh, J., Pomper, M., Tangerman, A., Wagner, C., Stabler, S. P., Allen, R. H., Mudd, S. H., and Braverman, N. Progressive cerebral edema associated with high methionine levels and betaine therapy in a patient
- Talukdar R, Murthy HV, Reddy DN. Role of methionine containing antioxidant combination in the management of pain in chronic pancreatitis: a systematic review and meta-analysis. Pancreatology 2015;15(2):136-44. PubMed
- 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
- Khairan P, Sobue T, Eshak ES, et al. Association of B Vitamins and Methionine Intake with the Risk of Gastric Cancer: The Japan Public Health Center-based Prospective Study. Cancer Prev Res (Phila) 2022;15(2):101-110. PubMed
Proline 4 references
- Jennings A, MacGregor A, Spector T, Cassidy A. Amino acid intakes are associated with bone mineral density and prevalence of low bone mass in women: Evidence from discordant monozygotic twins. J Bone Miner Res. 2016;31(2):326-35. PubMed
- Gracia-Marco L, Bel-Serrat S, Cuenca-Garcia M, et al. Amino acids intake and physical fitness among adolescents. Amino Acids. 2017;49(6):1041-1052. PubMed
- Jamdar J, Rao B, Netke S, et al. Reduction in tibial shaft fracture healing time with essential nutrient supplementation containing ascorbic acid, lysine, and proline. J Altern Complement Med. 2004;10(6):915-6.
- Mehl AA, Damião AO, Viana SD, Andretta CP. Hard-to-heal wounds: a randomised trial of an oral proline-containing supplement to aid repair. J Wound Care 2021;30(1):26-31. PubMed
Glycine 5 references
- 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
- Potkin SG, Jin Y, Bunney BG, Costa J, Gulasekaram B. Effect of clozapine and adjunctive high-dose glycine in treatment-resistant schizophrenia. Am J Psychiatry 1999;156:145-7.. PubMed
- Gusev EI, Skvortsova VI, Dambinova SA, et al. Neuroprotective effects of glycine for therapy of acute ischaemic stroke. Cerebrovasc Dis 2000;10:49-60. PubMed
- Inagawa K, Kawai N, Ono K, Sukegawa E, Tsubuku S, Takahashi M. Assessment of acute adverse effects of glycine ingestion at a high dose in human volunteers. Seikatsu Eisei. 2006; 50:27-32.
- Woods SW, Walsh BC, Hawkins KA, Miller TJ, Saksa JR, D'Souza DC, Pearlson GD, Javitt DC, McGlashan TH, Krystal JH. Glycine treatment of the risk syndrome for psychosis: report of two pilot studies. Eur Neuropsychopharmacol. 2013 Aug;23(8):931-40. PubMed
Histidine 3 references
Threonine 4 references
- 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
- Lee A, Patterson V. A double blind study of L-threonine in patients with spinal spasticity. Acta Neurol Scand 1993;88:334-8. PubMed
- Blin O, Pouget J, Aubrespy G, et al. A double-blind placebo controlled trial of L-threonine in amyotrophic lateral sclerosis. J Neurol 1992;239:79-81.
- Roufs JB. L-threonine as a symptomatic treatment for amyotrophic lateral sclerosis (ALS). Med Hypotheses 1991;34:20-3. PubMed
Serine 3 references
- 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.
- 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
- 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
Parts of this content are provided by the Therapeutic Research Center, LLC.
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.
© 2021 Therapeutic Research Center, LLC