GLP-1 medicines — side-effect literacy

Common side effects — most users, especially at start

• Nausea — most commonly reported. Usually worst in the first few days after a dose increase and settles over a week or two.
• Vomiting — sometimes follows nausea, particularly with larger meals or fatty foods.
• Diarrhoea — common early; usually self-limiting.
• Constipation — equally common in some users; hydration and fibre help.
• Reduced appetite, early satiety — the mechanism of action manifesting; not technically a side effect.
• Fatigue — often related to reduced calorie intake during the first weeks; usually improves.
• Injection-site reactions — minor redness or itching; rotating injection sites helps.

Slow titration is the single biggest tool for managing these. If a dose step is hard, talk to your prescriber about holding at the current dose for longer rather than pushing through.

Less-common but documented effects

• Gallbladder issues — gallstones and cholecystitis are documented at elevated rates. Right-upper-quadrant abdominal pain after meals warrants assessment.
• Hair shedding — anecdotally reported, often associated with rapid weight loss generally; usually transient.
• Lean-mass loss — alongside fat loss; resistance training and adequate protein intake help.
• Vivid dreams or insomnia — reported anecdotally; mechanism not well characterised.
• Heart rate increase — small mean increase reported in trials.

Rare but serious — seek urgent advice

• Acute pancreatitis — severe persistent abdominal pain, often radiating to the back, sometimes with nausea/vomiting. Call NHS 111 or 999 if severe.
• Severe allergic reaction (anaphylaxis) — facial / throat swelling, difficulty breathing. Call 999.
• Diabetic retinopathy progression in people with type 2 diabetes — rapid glucose drop can transiently worsen retinopathy. Ophthalmology review is part of standard care for this group.
• Severe hypoglycaemia — uncommon on GLP-1 monotherapy but elevated risk if combined with sulfonylureas or insulin.
• Suicidal thoughts — investigated as a potential signal; current regulatory position is that no causal link has been established, but if you experience new or worsening psychiatric symptoms while on a GLP-1 medicine, contact your prescriber and consider stopping. NHS 111 / 999 for acute risk.

What to do if you suspect a side effect

1. Routine: contact your prescriber. Adjust dose, timing, or stop per their advice.
2. Urgent but non-emergency: NHS 111.
3. Emergency: 999.
4. Report: via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk or the Yellow Card app. Patient and clinician reports are both welcome. See our Yellow Card page.