My husband has been taking them for several years, since he started intensive Chemo treatment. The only side effect he ever had was a bit of a rash, sometimes. We definitely feel it is thanks to the Amino Acids. He has looked and felt great ever since. I am now also taking them and feel so good with them. We recommend them to all our friends., many who buy them now and love them. It is a wonderful, underrated supplement that every person, at least over 60 should be taking!!!