Peptide side effects

What side effects do FDA-approved peptide drugs cause?

Wegovy's label reports nausea in 44% of patients versus 16% on placebo, diarrhea 30% vs 16%, vomiting 24% vs 6%, and constipation 24% vs 11% [1]. Permanent discontinuation from a gastrointestinal reaction happened in 4.3% of Wegovy patients versus 0.7% on placebo [1]. The label carries a boxed warning on thyroid C-cell tumors and lists acute pancreatitis, gallbladder disease and hypoglycemia as additional risks [1].

What are the risks of unapproved compounded peptides?

FDA's recurring concern with unapproved compounded peptides is immunogenicity risk from aggregation and peptide-related impurities [2]. Case reports cited by FDA link melanotan II to melanoma, priapism and other serious events, and cite a death reported after intravenous ipamorelin [2]. A 2026 review found many unapproved peptides show favorable results in animal models, but human safety data remain scarce, with potential for serious harm [3]. FDA also reported at least 30 patients with adverse events after intravenous glutathione, with symptoms including "fever, chills, pain, dizziness, signs of shock and sepsis-like symptoms" [4].