Berberine Side Effects

Berberine is poorly absorbed, so much of a dose stays in the gut. That is where the complaints show up.

In Yin et al. (2008), adults with type 2 diabetes took 0.5 g three times a day for 13 weeks. 34.5% reported gut side effects: diarrhea (10.3%), constipation (6.9%), flatulence (19.0%), and abdominal pain (3.4%). Most happened in the first four weeks. About a quarter (24.1%) cut back to 0.3 g three times a day, and the symptoms eased. The authors reported no liver or kidney damage in that trial (Yin 2008).

Trial protocols often split the day's amount across meals. That is a description of what those trials did, not a dose to copy. The amounts in the trials were often 0.9–1.5 g a day. What berberine did and did not change in the larger pools is on berberine.

In the trials cited here, liver enzymes did not rise on berberine. Yin 2008 reported no liver damage over 13 weeks. A 2024 systematic review reported no serious adverse events in the trials it pooled (Wang 2024). Those trials ran for weeks to months, not years, and most excluded people who already had liver disease. If you have liver disease or take drugs that strain the liver, ask your doctor first.

In Guo et al. (2012), healthy volunteers took 300 mg three times a day for two weeks. Berberine reduced the activity of CYP2D6, CYP2C9, and CYP3A4, enzymes that break down many prescription drugs. Exposure to midazolam, a CYP3A4 test drug, rose by about 40% (Guo 2012).

Diabetes drugs (metformin, insulin, sulfonylureas): trials also measured lower blood sugar, so taking berberine with those drugs can push glucose too low. That is a stacking risk, not a reason to swap a prescription for a supplement.

Cyclosporine: NCCIH warns berberine can raise its levels. Drugs cleared by CYP3A4, CYP2D6, or CYP2C9 include some statins, some blood thinners, many antidepressants, and some blood-pressure drugs. Ask a pharmacist to check your list.