Epicatechin: Research, Side Effects, and Safety of the Cocoa Flavanol

(-)-Epicatechin has a favorable safety record in the human studies that exist: a phase 1 study of the purified compound reported no adverse effects, and cocoa-flavanol trials report mainly mild gastrointestinal complaints. The largest relevant trial, COSMOS (21,442 older adults followed for a median of 3.6 years), found "no safety concerns" with a cocoa extract that contained epicatechin. The limits are that trials of purified epicatechin are small and short, and that most long-term data come from mixed cocoa extracts rather than epicatechin alone.

This guide summarizes the research, the side effects reported, and the practical cautions for prescribers.

Educational content for licensed healthcare professionals. Not medical advice; dosing and treatment decisions belong to the prescribing clinician.

What Epicatechin Is

(-)-Epicatechin is a flavanol, a type of plant polyphenol and a small molecule, found naturally in cocoa and tea [7]. It is the compound most strongly linked to the vascular effects of flavanol-rich cocoa: in healthy men, purified (-)-epicatechin reproduced the acute nitric-oxide-dependent improvement in flow-mediated dilation seen after cocoa [1]. Interest in muscle comes from human studies in which it raised plasma follistatin and lowered myostatin [2][3][4]. See the Epicatechin library page for background, and our Follistatin-344 page for the myostatin pathway.

Epicatechin Research and Safety: Evidence Table

What the Human Studies Show

Phase 1 safety and pharmacokinetics. In a two-part open-label study, healthy volunteers received purified (-)-epicatechin as single or repeated oral administration for five days. It was well tolerated and readily absorbed, with phase 2 metabolism. The authors reported increases in plasma nitrite, platelet mitochondrial enzyme activity, and plasma follistatin, and stated it was "safe to use, with no observed adverse effects" [2]. The study was small (17 participants) and short.

Becker muscular dystrophy. In an open-label study of seven ambulatory adults, eight weeks of (-)-epicatechin increased markers of mitochondrial biogenesis and muscle regeneration on biopsy, raised muscle and plasma follistatin, lowered myostatin, and improved exercise-test parameters [3]. No placebo group was used.

Sarcopenia. In a randomized, double-blind trial of 62 older men with sarcopenia, epicatechin alone and combined with resistance training improved appendicular muscle mass index and timed up-and-go compared with placebo; the combination produced the largest gains in strength and the follistatin/myostatin ratio [4].

Vascular markers. In 37 (pre)hypertensive adults, four weeks of pure epicatechin lowered soluble E-selectin, a marker of endothelial dysfunction, though the composite endothelial score fell short of significance [7].

None of these studies was designed or powered to detect uncommon adverse effects.

Long-Term Safety From Cocoa-Flavanol Trials

COSMOS. This randomized, double-blind, placebo-controlled trial assigned 21,442 US adults aged 60 or older to a cocoa extract supplement containing flavanols, including (-)-epicatechin, or placebo. Over a median of 3.6 years, the extract did not significantly reduce total cardiovascular events, but cardiovascular death was 27% lower. The authors reported no safety concerns [6].

Cochrane review. Across 35 trials and 1,804 mainly healthy participants, flavanol-rich cocoa lowered blood pressure by about 2 mmHg over two to 18 weeks. Adverse effects, mainly gastrointestinal complaints and nausea, were reported by 1% of participants on active cocoa and 0.4% of controls [5]. The reviewers called for longer trials to assess potential adverse effects of chronic intake.

These data are reassuring, but they describe cocoa extracts and cocoa products, which contain other flavanols and often methylxanthines such as caffeine and theobromine. They do not fully characterize higher-intake or long-term use of purified epicatechin.

Who Should Be Cautious

• Pregnancy and breastfeeding: purified epicatechin has not been studied; dietary intake from food is a different exposure.
• Patients on antihypertensives or with low blood pressure: cocoa flavanols produce a small blood-pressure reduction [5].

• Patients sensitive to caffeine or theobromine if the product is cocoa-derived rather than purified.
• Hormone-sensitive or reproductive concerns: epicatechin raised plasma follistatin in human studies [2][3][4]; the clinical significance is unknown.
• Children, for whom there are no supplement trials.

Monitoring Considerations for Prescribers

• Blood pressure at baseline and follow-up in patients on antihypertensive therapy.
• GI tolerance at the first follow-up.
• Product identity: ask whether the product is purified (-)-epicatechin or a cocoa or green-tea extract, because the composition and the risk profile differ.
• Muscle-focused goals: if epicatechin is used for muscle, track objective strength or function measures rather than relying on biomarker claims. See our peptides for muscle growth guide.

Regulatory Status (October 2026)

(-)-Epicatechin is not an FDA-approved drug. It is a naturally occurring dietary flavanol and is sold as a dietary-supplement ingredient. It is not a peptide and is not tracked on our FDA Peptide Status Tracker. Supplement-grade products are not reviewed by FDA for identity or potency before sale, so third-party testing matters.

Frequently Asked Questions

Does epicatechin have side effects?

In a phase 1 study of purified epicatechin, no adverse effects were observed. In cocoa-flavanol trials, the most common complaints were mild gastrointestinal symptoms and nausea, reported by about 1% of participants.

Is epicatechin safe long term?

The best long-term data come from COSMOS, in which more than 21,000 older adults took a cocoa extract containing epicatechin for a median of 3.6 years with no safety concerns. Long-term studies of purified epicatechin alone have not been done.

Does epicatechin raise follistatin?

Small human studies in healthy volunteers, adults with Becker muscular dystrophy, and older men with sarcopenia reported higher plasma follistatin and, in some, lower myostatin. Whether this translates into meaningful muscle gains is not established.

Does epicatechin lower blood pressure?

Flavanol-rich cocoa lowered blood pressure by about 2 mmHg in a Cochrane meta-analysis, with larger reductions in people with hypertension. Patients on blood pressure medication should have their readings checked.

Is epicatechin a peptide?

No. Epicatechin is a plant flavanol, a small molecule found naturally in cocoa and tea. It is grouped with peptides on some sites because of its proposed effects on the myostatin pathway.

Newtropin does not prescribe, compound, or dispense. We connect licensed providers with licensed 503A compounding partners; prescribers can start at For Providers. For more on the myostatin pathway, see our follistatin-344 article.

References

1. Schroeter H, et al. (-)-Epicatechin mediates beneficial effects of flavanol-rich cocoa on vascular function in humans. Proc Natl Acad Sci U S A. 2006;103(4):1024-9. PubMed
2. Barnett CF, et al. Pharmacokinetic, partial pharmacodynamic and initial safety analysis of (-)-epicatechin in healthy volunteers. Food Funct. 2015;6(3):824-33. PubMed
3. McDonald CM, et al. (-)-Epicatechin induces mitochondrial biogenesis and markers of muscle regeneration in adults with Becker muscular dystrophy. Muscle Nerve. 2021;63(2):239-249. PubMed
4. Mafi F, et al. Improvement in skeletal muscle strength and plasma levels of follistatin and myostatin induced by an 8-week resistance training and epicatechin supplementation in sarcopenic older adults. J Aging Phys Act. 2019;27(3):384-391. PubMed
5. Ried K, et al. Effect of cocoa on blood pressure. Cochrane Database Syst Rev. 2017;4(4):CD008893. PubMed
6. Sesso HD, et al. Effect of cocoa flavanol supplementation for the prevention of cardiovascular disease events: the COcoa Supplement and Multivitamin Outcomes Study (COSMOS) randomized clinical trial. Am J Clin Nutr. 2022;115(6):1490-1500. PubMed
7. Dower JI, et al. Supplementation of the pure flavonoids epicatechin and quercetin affects some biomarkers of endothelial dysfunction and inflammation in (pre)hypertensive adults: a randomized double-blind, placebo-controlled, crossover trial. J Nutr. 2015;145(7):1459-63. PubMed