What are the most common side effects of peptide use?

The most common side effects include injection site reactions such as redness or swelling, headaches, nausea, and fatigue. Gastrointestinal effects like nausea, vomiting, and diarrhea are particularly common with metabolic peptides like GLP-1 agonists, though these often diminish as the body adjusts to treatment. Some individuals may also experience hormonal fluctuations or cardiovascular changes depending on the specific peptide used.