What are the most common side effects of GLP-1s?

The common tier (trial frequencies, semaglutide/tirzepatide): | Side effect |, usually transient | | Constipation | 15–25% | Slowest to resolve; needs active management | | Vomiting | 10–25% | Usually with rushed titration or large/fatty meals | | Fatigue | ≈10% | First weeks; often intake-related | | Reflux/burping | ≈10% | Slowed stomach emptying | | Injection-site reactions | <10% | Mild, rotate sites | The headline statistic that contextualizes all of it: despite those frequencies, only 4–7% of trial participants quit due to side effects. The gap is management — slow titration, smaller meals, hydration, and a practical playbook that works. The serious-but-uncommon tier: pancreatitis (what to watch for), gallbladder disease (partly a rapid-weight-loss effect — details), worsening of diabetic eye disease in some diabetes patients, hypoglycemia when combined with insulin/sulfonylureas, and the boxed thyroid warning based on rodent findings. The cosmetic/structural tier people ask about: hair shedding, muscle loss, and “Ozempic face” — all primarily consequences of rapid weight loss itself rather than drug toxicity, and all blunted by slower loss, protein, and resistance training. Know the red-flag symptoms before you start — they’re rare, but recognizing them early is the whole game.