These are among the best-studied drugs in metabolic medicine, and most side effects are gastrointestinal, dose-related and temporary. A few warnings deserve real attention, and a couple of feared ones turn out weaker than the headlines. This is an overview, not a full safety profile.
Nausea (reported in ~14–58% across trials, commonly ~44% early), plus diarrhoea, constipation and vomiting. They are dose-dependent, peak during titration, and usually fade with time. They are the main reason people stop — but only ~1–4% actually discontinue for GI reasons. Slow titration, smaller meals and hydration help. Evidence ●●●●●
Gallstones and gallbladder disease are genuinely raised (~1.4×, higher with weight-loss doses and rapid loss — partly a consequence of fast weight loss itself). Pancreatitis is on the label, but pooled randomised data have not confirmed a real increase; the warning is precautionary. Severe, persistent abdominal pain warrants stopping and prompt review.
The black-box warning comes entirely from rodent studies, where these drugs caused thyroid C-cell tumours; human C-cells carry far fewer receptors and human causality is unproven, with large studies not showing raised thyroid cancer. Still, they are firmly contraindicated with a personal or family history of medullary thyroid carcinoma or MEN 2. Evidence ●○○○○ for human risk
Because they slow the stomach, there are rare reports of ileus (bowel stall) and occasional persistent gastroparesis, and retained stomach contents can raise aspiration risk under sedation. Tell any surgeon or anaesthetist you are on a GLP-1; current guidance individualises whether to pause it rather than always stopping.
Cardiovascular safety is favourable — semaglutide cut major cardiac events 20% (SELECT); tirzepatide is CV-neutral to positive. A suicidality signal was investigated and not confirmed, and regulators asked for the warning to be removed. ‘Ozempic face’ (facial hollowing) is just the normal fat loss of any rapid weight loss, not a specific drug effect. The real substantive issue is muscle loss — covered in the muscle section. Evidence ●●●●○
Not a complete safety profile
This summarises the main signals only; it omits contraindications, interactions (e.g. with insulin or sulfonylureas), pregnancy cautions and individual risk factors. Whether one of these drugs is safe for you is a clinical judgement — make it with a prescriber, not from a guide.
The Weight Loss Guide