I stumbled onto this product looking for a high-quality PQQ supplement. Not being familiar with Berberine, I did some quick internet research and decided that it sounded like a great addition to my nutritional regimen. Received order in a timely manner and began to take 1/day. Fast foward 3ish weeks later: I think I'm having appendicitis or a cyst is rupturing or I'm dying, the lower abdominal pain is so intense. A couple days later, I feel like my old self again and resume my daily supplements and I'm vomiting and experiencing diarrhea for hours on end, which is super weird for me, my stomach and I are on great terms always. So I'm like, 'oh it must be a new supplement I'm intoducing' and look into potential side effects. I totally forgot about the Berberine (bc I purchased it for the PQQ) and PQQ effects don't touch on gastritis/etc so I'm thinking this product is cool and no worries and it's the other one I purchased the same time as this. Today I feel great, resume my full supplement regimen (minus the one I think was creating adverse effects), and 4ish hrs, I'm dying inside again. So, in between puking, emitrol, and imodium, I look up Berberine. It's a thing, people. Long story long: if you don't experience these side effects, I'm sure this is a wonderful product. If you do experience these side effects, however, it's the worst supplement I have ever taken.