Almost everyone who takes a GLP-1 gets side effects. For most people they are unpleasant rather than dangerous, concentrated around dose increases, and manageable with some practical adjustments. A small number are serious and need immediate attention. This guide covers both, and what actually helps.
This is general information, not advice about your case
The common ones
These are the effects listed as most common across the semaglutide, tirzepatide and orforglipron labels. They are a direct consequence of how the drugs work - slowing gastric emptying and altering appetite signalling - which is why they cannot be engineered away entirely.
- •Nausea - the most common by a distance, and the most common reason people stop
- •Constipation - often the most persistent, and the one people underestimate
- •Diarrhoea
- •Vomiting
- •Indigestion, heartburn, belching and gas
- •Abdominal pain and bloating
- •Headache and fatigue
- •Injection-site reactions on the injectable forms
- •Hair loss - listed on the orforglipron label and widely reported with rapid weight loss generally
What actually helps
For nausea
- •Eat smaller portions and stop at the first sign of fullness rather than finishing the plate
- •Avoid high-fat and heavily fried food, which sits in a slowed stomach for longer
- •Do not lie down straight after eating
- •Sip fluids through the day rather than drinking large volumes with meals
- •Bland, dry foods early in the day are tolerated better by most people
- •Ask your prescriber about slowing the titration - this is a standard, legitimate adjustment
For constipation
- •Fluid intake matters more than most people expect, particularly if you are eating far less
- •Fibre helps, but increase it gradually or you will trade constipation for bloating
- •Daily movement helps genuinely, not just as generic advice
- •Ask your prescriber before starting a laxative or stool softener, especially long-term
For fatigue
- •Much of it comes from eating substantially less. Protein intake in particular tends to fall further than people realise
- •Check that you are not dehydrated - it is easy to drink less when you are eating less
- •Persistent fatigue is worth investigating rather than assuming it is just the drug
The serious warnings
These appear in the prescribing information for the approved GLP-1 medications. They are uncommon, but they are the reason these drugs need a prescriber rather than a checkout page.
| Warning | What to watch for | What to do |
|---|---|---|
| Thyroid C-cell tumours (boxed warning) | A lump or swelling in the neck, hoarseness, trouble swallowing, shortness of breath | Tell your provider. Contraindicated if you or a family member has had medullary thyroid carcinoma or MEN 2 |
| Pancreatitis | Severe, persistent abdominal pain, sometimes radiating to the back, with or without vomiting | Stop the medication and seek medical help immediately |
| Gallbladder problems | Upper abdominal pain, fever, jaundice, clay-coloured stools | Contact your provider promptly |
| Dehydration and kidney injury | Vomiting or diarrhoea that will not settle, reduced urination, dizziness | Rehydrate and contact your provider; kidney function can be affected |
| Hypoglycaemia | Shakiness, sweating, confusion, blurred vision, fast heartbeat | Highest risk when combined with insulin or a sulfonylurea; doses of those usually need adjusting |
| Serious allergic reaction | Swelling of face, lips, tongue or throat, difficulty breathing, severe rash, fainting | Emergency care immediately |
| Aspiration under anaesthesia | Not a symptom - a procedural risk from delayed gastric emptying | Tell every surgeon and anaesthetist before any procedure |
| Diabetic retinopathy changes | Vision changes, particularly in people with type 2 diabetes | Report to your provider |
A note on compounded products
The side-effect profiles above come from the FDA-approved medications, where the formulation, dose and manufacturing were reviewed. Compounded semaglutide and tirzepatide use the same active ingredients but have not been through that review, and formulations vary between pharmacies - some add B12, ondansetron or other ingredients. Dosing errors have been a documented problem where products are supplied in vials requiring the patient to draw up a dose.
If you are using a compounded product, being clear about exactly what you are injecting and at what concentration matters more, not less. More on compounded medication.
When to call rather than push through
- •Severe abdominal pain that does not resolve
- •Vomiting or diarrhoea you cannot keep ahead of with fluids
- •Any sign of an allergic reaction
- •Symptoms that persist at a stable dose rather than easing over one to two weeks
- •Anything that frightens you - a good provider would rather hear from you early
Providers differ enormously in how reachable they are when this happens. Some publish 24/7 clinical access; others offer an email address and no stated hours. That difference is invisible when you are comparing prices and very visible at 11pm on a Sunday.