Studies conducted on resveratrol supplements have shown that there are no major negative side effects of resveratrol and resveratrol supplements.
The only major side effects found in research are positive ones. Infact, the research on resveratrol supplementation has shown that resveratrol supplement side effects consist of a lower risk of heart disease, a potential increase in energy levels, weight loss due to an increase in metabolism, and a potential to cure certain types of cancer, to name just a few.
The tests mentioned above refer to those done on lab mice, although the effects above seem to be consistent with those found in the french paradox, whereby the French population consume far more resveratrol than most nations, and are thought to live a healthier life as a result.
Minor resveratrol side effects found by Dr Sinclair in his original research were discovered when the study participants took between 500mg and 5000mg of resveratrol per day. The minor side effects of resveratrol found include diarrhea and vomiting in "a small number of people".
Although the human tests were completed with 500mg to 5000mg daily doses, Dr Sinclair recommends that if you're thinking of trying resveratrol supplements, try taking doses of no more than 250mg, first.