It's probably the Metformin
from Wicki.........
The most common
adverse effect of metformin is gastrointestinal upset, including
diarrhea, cramps, nausea, vomiting and increased
flatulence; metformin is more commonly associated with gastrointestinal side effects than most other antidiabetic drugs.
[17] The most serious potential side effect of metformin use is lactic acidosis; this complication is very rare, and the vast majority of these cases seem to be related to comorbid conditions, such as impaired liver or kidney function, rather than to the metformin itself.
[51]