Nausea, reduced appetite and digestive changes are the most common effects, usually strongest after a dose increase and settling within days. Slow dose escalation is the best prevention.
Why side effects happen
These medicines deliberately slow gastric emptying. That is how they create lasting fullness — and it is also why nausea, reflux and altered bowel habit occur.
The body adapts. Effects are almost always strongest in the days following a dose increase, then settle.
The common effects
Nausea is the most frequently reported. Vomiting, constipation, diarrhoea, reflux, burping, fatigue and headache also occur.
Most are mild to moderate and improve as your body adjusts to each dose level.
Practical ways to reduce them
Eat smaller portions and stop at the first sign of fullness rather than finishing what is served. Eat slowly. Avoid very fatty, fried or heavily spiced meals in the days after a dose increase.
Keep fluids up, prioritise protein, and add fibre gradually if constipation is an issue. Many patients find that eating their main meal earlier in the day helps.
Effects that need medical attention
Contact your doctor promptly for severe or persistent abdominal pain, particularly if it radiates to the back, as this can indicate pancreatitis. Persistent vomiting, signs of dehydration, or severe upper-right abdominal pain also warrant urgent contact.
You will be given clear guidance on which symptoms need same-day contact before you start treatment.
Why supervision matters
Most patients who stop treatment do so because side effects were not managed, not because the medicine failed. A slower ladder, a temporary dose hold or supportive medication usually resolves the problem.
This is why doses are adjusted at reviews rather than independently.
Managing nausea specifically
Eat smaller amounts more often rather than three large meals. Stop at the first sign of fullness. Avoid lying down immediately after eating. Bland, lower-fat foods are better tolerated in the days after a dose increase.
Ginger, cold water and fresh air help some patients. If nausea persists beyond a few days or prevents adequate intake, contact your team rather than pushing through.
Constipation and how to prevent it
Slower gastric emptying plus reduced food and fluid intake makes constipation extremely common. Prevention works better than treatment: deliberate hydration, gradual fibre increase, and daily movement.
Your doctor may advise a stool softener. Do not start laxatives routinely without discussing it first.
Effects on other medications
Because gastric emptying slows, absorption of some oral medicines can change. Oral contraceptives, thyroid medication and certain diabetes drugs may need review.
If you take insulin or a sulfonylurea, doses frequently require reduction to avoid hypoglycaemia. Never adjust these yourself.
Frequently asked questions
How long do side effects last?
Can side effects be prevented?
Should I stop if I feel nauseous?
Do side effects mean it's working?
Is hair loss a side effect?
Medical disclaimer. This article is general information, not medical advice, and does not replace consultation with a qualified doctor. The medicines discussed are prescription-only and must be prescribed and monitored by a physician. Outcomes vary between individuals. Never start, stop or change a prescribed medicine without medical advice.