At the doses most people take (around 500 mg to 1 g per day), resveratrol is well tolerated in clinical trials, and the NIH’s LiverTox database rates it “unlikely” to cause clinically apparent liver injury. The side effects that do appear are mainly gastrointestinal and dose-related, showing up at 2.5 g and 5 g per day. The more practical concern for many people is drug interactions: resveratrol changed the activity of several drug-metabolizing enzymes in a human study, and Memorial Sloan Kettering advises talking to a provider before combining it with blood thinners.
Table of Contents
- Side Effects: What Human Trials Reported
- Does Dose Change the Picture?
- Liver Enzymes: What NIH LiverTox Says
- Drug Interactions
- Who Should Talk to a Clinician First
- Why Product Quality Is Part of Safety
Side Effects: What Human Trials Reported
The most-cited safety study is a repeat-dose trial in 40 healthy volunteers (Brown et al., Cancer Research, 2010). Participants took 0.5, 1.0, 2.5 or 5.0 g of resveratrol daily for 29 days. The researchers found that most adverse events at the two highest doses (2.5 and 5.0 g) were gastrointestinal: nausea, flatulence, abdominal discomfort and diarrhea. Most were mild, four participants had moderate symptoms, the symptoms began two to four days into treatment and resolved within two days of stopping. No serious adverse reactions were detected in clinical, biochemical or hematologic analyses.
What the authors concluded: the compound was judged safe overall, but they suggested that in future studies the daily dose “should perhaps not exceed 1.0 g” because of gastrointestinal tolerability at higher doses. That is a trial recommendation, not a medical dosing guideline, but it is a useful reference point.
Does Dose Change the Picture?
Yes. In that trial, the gastrointestinal effects were concentrated at 2.5 and 5.0 g per day, which is well above typical supplement doses. Memorial Sloan Kettering’s summary of the evidence says the same thing: mild to moderate gastrointestinal symptoms and diarrhea at high doses, with the common reports being nausea, gas, abdominal pain and diarrhea. If you are getting stomach upset, the first thing the data points to is dose; our resveratrol dosage guide covers how studies have approached dosing.
Liver Enzymes: What NIH LiverTox Says
The NIH’s LiverTox database reviews resveratrol’s effect on the liver. Its summary: most studies showed no ALT elevations or only rare, mild increases. In studies using high doses (1.5 to 3.0 g daily), average serum ALT and AST rose slightly during treatment and fell back to the normal range promptly after stopping. In one study of people with fatty liver disease taking 1,500 mg twice daily, median ALT rose from 25 to 63 U/L and AST from 35 to 45 U/L. LiverTox reports no published cases of clinically apparent liver injury attributed to resveratrol, and gives it a likelihood score of “E” (unlikely cause of clinically apparent liver injury).
Why this matters: the liver-marker changes were seen at doses several times higher than typical supplement doses, and they reversed after stopping. But if you have a liver condition or take medications processed by the liver, high-dose resveratrol is something to raise with your clinician first.
Drug Interactions
Interactions are where the evidence is most relevant to everyday use.
Drug-metabolizing enzymes. In a healthy-volunteer study (Chow et al., Cancer Prevention Research, 2010), resveratrol at 1 g daily for four weeks inhibited the enzymes CYP3A4, CYP2D6 and CYP2C9 and induced CYP1A2, according to the summary at Memorial Sloan Kettering. These enzymes process a large share of prescription medications, so in principle resveratrol could raise or lower blood levels of some of them. The study showed the enzyme effect; it did not test specific drug combinations, so how much this matters for any particular medication is something a pharmacist or prescriber can check.
Blood thinners. Memorial Sloan Kettering advises talking with your healthcare provider if you take blood thinners such as warfarin, because resveratrol may increase the risk of bleeding. We did not find controlled trials that quantify that risk, so treat it as a precaution rather than a measured effect.
Animal data. MSKCC also notes a mouse study in which a resveratrol-rich Polygonum cuspidatum supplement raised blood levels of the anticonvulsant carbamazepine through CYP3A inhibition. That is animal evidence, not human.
Who Should Talk to a Clinician First
Based on the sources above, it is sensible to speak with a doctor or pharmacist before taking resveratrol if you:
- take blood thinners or antiplatelet medication
- take prescription drugs processed by CYP3A4, CYP2D6 or CYP2C9
- have a liver condition
- have a hormone-sensitive condition (Memorial Sloan Kettering urges caution because resveratrol shows estrogen-like activity)
- are pregnant or breastfeeding, or are managing any medical condition
Why Product Quality Is Part of Safety
All of the trials above used defined, high-purity resveratrol. A product that is mislabeled, diluted or poorly characterized can’t be assumed to behave the same way, and you can’t judge your dose if you don’t know what’s in the capsule. That is why we recommend starting from pure resveratrol with a published certificate of analysis. See Mega Resveratrol’s third-party-tested capsules, and for a wider overview of the compound, our Resveratrol A to Z guide.
Frequently Asked Questions
What are the side effects of resveratrol?
In clinical trials the main side effects are gastrointestinal: nausea, gas, abdominal discomfort and diarrhea, mostly at high doses (2.5 g and 5 g per day) in a 29-day trial of 40 healthy volunteers.
Is resveratrol safe for your liver?
NIH LiverTox rates it “unlikely” to cause clinically apparent liver injury and reports no published cases. At high doses (1.5 to 3 g daily), ALT and AST rose slightly and returned to normal after stopping.
Does resveratrol interact with medications?
It can. In a human study, 1 g daily for four weeks inhibited the CYP3A4, CYP2D6 and CYP2C9 enzymes and induced CYP1A2. Memorial Sloan Kettering also advises caution with blood thinners such as warfarin. Ask a pharmacist or prescriber about your specific medications.
What dose of resveratrol is too much?
There is no official upper limit. In the main dose-escalation trial, gastrointestinal effects appeared at 2.5 g and 5 g daily, and the authors suggested future studies keep the dose to about 1 g per day or less.
Can you take resveratrol with blood thinners?
Talk to your healthcare provider first. Memorial Sloan Kettering says resveratrol may increase bleeding risk. We did not find controlled trials measuring the size of that risk.
Conclusion
Resveratrol’s safety record in human trials is reassuring at typical doses, with dose-related stomach upset and, at high doses, small reversible liver-enzyme changes. The part that deserves more attention than it usually gets is medication interactions. If you take prescription drugs, checking with a clinician or pharmacist is the step that matters most.
Disclaimer: This article is for informational purposes only and does not constitute medical advice. These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease. Consult a qualified healthcare professional before starting any new supplement, especially if you are pregnant, nursing, taking medication, or have a medical condition.
Resources cited:
- Brown VA, et al. “Repeat Dose Study of the Cancer Chemopreventive Agent Resveratrol in Healthy Volunteers: Safety, Pharmacokinetics, and Effect on the Insulin-like Growth Factor Axis.” Cancer Research. 2010;70(22):9003-9011. https://aacrjournals.org/cancerres/article/70/22/9003/561017/Repeat-Dose-Study-of-the-Cancer-Chemopreventive
- Chow HH, et al. “Resveratrol Modulates Drug- and Carcinogen-Metabolizing Enzymes in a Healthy Volunteer Study.” Cancer Prevention Research. 2010;3(9):1168-1175. https://aacrjournals.org/cancerpreventionresearch/article/3/9/1168/49499/Resveratrol-Modulates-Drug-and-Carcinogen
- LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. “Resveratrol.” NIH / NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK548465/
- Memorial Sloan Kettering Cancer Center, Integrative Medicine. “Resveratrol.” https://www.mskcc.org/cancer-care/integrative-medicine/herbs/resveratrol
