Foundayo: stomach first, liver later
Nausea, vomiting, diarrhea, and constipation are the common ones, mostly mild to moderate and concentrated in the escalation weeks. In the pooled label data, 8% of people stopped because of side effects (3% on placebo).
The boxed warning
Like every GLP-1 drug, Foundayo carries a boxed warning for thyroid C-cell tumors based on rodent findings for the class. Human relevance hasn’t been established. It’s contraindicated if you or a family member have had medullary thyroid carcinoma or MEN 2.
Pancreas and gallbladder
Acute pancreatitis was adjudicated in 6 Foundayo-treated patients across the pooled trials (2 events in one placebo patient). Small numbers, but it’s on the label as a warning, along with acute gallbladder disease.
Low blood sugar
Rare on its own. In ACHIEVE-4, clinically significant hypoglycemia occurred in 6.8% on orforglipron against 19.2% on insulin glargine.
Liver: no signal
Given the class history above, this is the most important negative finding in the whole program.
Retatrutide: trial record and gray market
The trial record shows the same GI pattern at higher rates (nausea up to 60% in the top-exposure Phase 2 group), plus two things specific to it: a dose-related rise in heart rate and an unusual skin-sensitivity signal in 7% of participants.
Then there’s the gray-market record. On June 19, 2026, Victoria’s Chief Health Officer reported six cases of acute liver injury in people who had used unapproved products labelled as retatrutide, with a contaminant suspected rather than the molecule itself.
Conclusion
Foundayo’s side effects are a list on a label. Retatrutide’s are a list on a label plus whatever was in the vial. Those aren’t the same kind of risk.