Key takeaways
- The most common side effects are gastrointestinal — nausea, diarrhoea, vomiting and constipation — and they are usually worst in the first weeks after a dose increase.
- On the Wegovy label, 44% of people reported nausea — and so did 16% of people on placebo.
- Hair loss is on the label, at 3% versus 1% on placebo. It is uncommon, and it is usually a response to rapid weight loss rather than to the drug itself.
- In the trials, 6.8% of people stopped Wegovy because of side effects. 3.2% stopped placebo.
- Both medicines carry a boxed warning about thyroid tumours seen in rodents, and both are contraindicated for anyone with a personal or family history of medullary thyroid carcinoma or MEN 2.
- This page is education, not medical advice. These are prescription medicines and the decision belongs to you and your prescriber.
What are the most common GLP-1 side effects?
Below is the adverse-reaction table from the FDA prescribing information for Wegovy (semaglutide 2.4 mg), label revised April 2024. Every reaction listed occurred in at least 2% of people and more often than on placebo. The placebo column is the part that rarely gets quoted.
| Reported effect | Placebo (n=1,261) | Wegovy 2.4 mg (n=2,116) |
|---|---|---|
| Nausea | 16% | 44% |
| Diarrhoea | 16% | 30% |
| Vomiting | 6% | 24% |
| Constipation | 11% | 24% |
| Abdominal pain | 10% | 20% |
| Headache | 10% | 14% |
| Fatigue | 5% | 11% |
| Dyspepsia (indigestion) | 3% | 9% |
| Dizziness | 4% | 8% |
| Hair loss | 1% | 3% |
For Zepbound (tirzepatide), label revised April 2026, the same effects appear at broadly similar or slightly lower rates: nausea 25–29% against 8% on placebo, diarrhoea 19–23% against 8%, vomiting 8–13% against 2%, and hair loss 4–5% against 1%. Rates varied little between the 5, 10 and 15 mg doses.
Do GLP-1 side effects go away?
For most people the gastrointestinal effects are worst in the first days after starting and after each dose increase, then settle. This is why prescribing schedules escalate slowly rather than starting at the full dose. The label reflects the same pattern: the reactions that most often led people to stop were nausea, vomiting and diarrhoea, and they clustered early.
The more useful number is how many people found them intolerable enough to quit. In the Wegovy trials 6.8% discontinued because of adverse reactions, against 3.2% on placebo. Nausea specifically caused 1.8% to stop, versus 0.2% on placebo. So the large majority of people who experience side effects continue treatment.
If symptoms are still severe several weeks after a dose has stabilised, that is a reason to speak to the prescriber about the escalation schedule — not a reason to push through quietly.
Does semaglutide or tirzepatide cause hair loss?
It is on both labels, and it is uncommon: 3% on Wegovy against 1% on placebo, and 4–5% on Zepbound against 1%. So roughly one person in thirty reports it, and a third of that figure occurs without any drug at all.
The mechanism most consistent with the evidence is not the drug attacking hair. Rapid weight loss and a sharp drop in calorie and protein intake are long-recognised triggers for telogen effluvium — a temporary shift of hair follicles into the shedding phase, which shows up two to three months after the trigger and typically recovers. People who lose weight quickly by other means report the same thing.
That distinction matters practically: if the driver is rapid loss and low protein intake rather than the molecule, then eating enough protein, not under-eating simply because appetite has gone, and losing weight at a sustainable rate are the levers that actually help.
Do GLP-1 medications cause muscle loss?
Muscle loss does not appear as an adverse reaction on either label. That is worth stating plainly, because it is frequently reported as though it were.
What is well established is broader: any substantial, rapid weight loss reduces lean mass as well as fat, whether it comes from a medication, surgery or a very low-calorie diet. The concern with GLP-1 medicines is not a unique muscle-wasting effect but the speed of loss combined with a suppressed appetite that makes adequate protein intake harder to achieve.
The response is the same as for any rapid weight loss: prioritise protein, keep resistance training in the week, and do not treat reduced appetite as licence to eat far too little. We cover the practical side of this on our GLP-1 support page.
Can GLP-1 medications affect mood?
The Wegovy label carries a specific warning: “Suicidal Behavior and Ideation: Monitor for depression or suicidal thoughts. Discontinue WEGOVY if symptoms develop.” That is a monitoring instruction to prescribers, and it is why anyone with a history of depression should raise it before starting rather than after.
Separately, fatigue is a listed reaction at 11% against 5% on placebo, and being persistently tired and eating very little will affect anyone’s mood regardless of pharmacology.
How do you manage nausea and constipation on a GLP-1?
These are the two effects people ask about most, and the practical measures are unglamorous:
- Smaller meals, eaten more slowly. These medicines slow gastric emptying, so the volume that felt normal before will not now.
- Stop at comfortably full, not full. Most reported nausea follows eating past the point the stomach is ready for.
- Fluid and fibre for constipation, and movement — the same measures that work for constipation generally.
- Fewer very high-fat and very large meals, which sit longest.
- Tell the prescriber before the next dose increase if the current dose is still difficult. Escalation schedules can be slowed.
Dehydration is the practical risk that ties these together: if vomiting or diarrhoea is significant, fluid intake matters more than usual, and persistent vomiting is a reason to seek care rather than to manage at home.
Can you drink alcohol on a GLP-1?
Neither label lists alcohol as a formal contraindication or interaction. That is not the same as saying it is inconsequential.
Alcohol irritates the stomach, and these medicines already slow gastric emptying — so the combination tends to amplify nausea. Alcohol also carries its own risk of low blood sugar, which matters considerably more for anyone also taking insulin or a sulfonylurea. And because appetite is suppressed, people drinking on a GLP-1 are more likely to be doing so having eaten very little.
Many people also report that these medicines simply reduce the desire to drink. That is a genuine and much-discussed observation, but it is not an approved use and should not be a reason anyone starts one.
Are there side effects specific to women?
Honestly: the labels do not break the common adverse reactions down by sex, so anyone presenting a female-specific side-effect list is going beyond what the trial data supports.
What the labels do address directly is pregnancy. These medicines are not recommended during pregnancy, and because weight loss and delayed gastric emptying can affect the absorption of oral contraception, anyone using an oral contraceptive should discuss whether an additional method is appropriate — particularly around dose increases. Anyone who is pregnant, trying to conceive, or breastfeeding should be having that conversation before starting.
What are the long-term side effects?
Both medicines carry a boxed warning — the FDA’s most serious — because in rodents semaglutide and tirzepatide caused dose-dependent thyroid C-cell tumours. The label is careful about what this means: “It is unknown whether WEGOVY causes thyroid C-cell tumors, including medullary thyroid carcinoma, in humans, as human relevance… has not been determined.” Both are contraindicated for anyone with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2.
Beyond that, the Wegovy label directs prescribers to monitor for acute pancreatitis, acute gallbladder disease, hypoglycaemia, acute kidney injury (usually secondary to dehydration from vomiting or diarrhoea), hypersensitivity reactions, diabetic retinopathy complications in people with type 2 diabetes, increased heart rate, and the mood changes described above.
These are the reasons the medicine is prescription-only and supervised. They are uncommon; they are also the specific things a prescriber is watching for.
Who should not take a GLP-1 medication?
- Anyone with a personal or family history of medullary thyroid carcinoma, or with MEN 2. This is an absolute contraindication on the label.
- Anyone with a known serious hypersensitivity to the medicine.
- Anyone pregnant, trying to conceive, or breastfeeding, without a prescriber’s specific guidance.
- Anyone with a history of pancreatitis, gallbladder disease, gastroparesis or significant kidney disease should raise it before starting, not after.
- Anyone with a history of depression or suicidal ideation, for the monitoring reason above.
When should you stop waiting and call someone?
How WholeHealth Hydration fits into this
We are a nurse-led practice. Meagan Williams is a Registered Nurse with critical-care certification, and everything on this page comes from the manufacturers’ own FDA prescribing information rather than from marketing material.
Where we help is the part around the medicine: hydration when GI effects have left someone depleted, and support through the phase where appetite is suppressed. We do not decide whether a GLP-1 is right for anyone — that is a conversation with a prescriber, and we will say so plainly if that is the answer. You can read what we do offer on the medical weight loss page, or compare the two medicines on our semaglutide versus tirzepatide comparison.