Guide
Managing Side Effects
Our side effects page lists what can happen. This one is about what to do — the practical adjustments that keep people on treatment, the symptoms that mean stop and call someone, and the two things most people are not told.
Gastrointestinal effects — nausea, vomiting, diarrhoea and constipation — are the common ones, and they are usually worst during dose escalation and settle as you adapt. Most are manageable. The point of this page is that "manageable" requires actually doing something, and that a handful of symptoms are not in that category at all. For the full list of what these medications can cause, see our side effects page.
What Actually Helps
Nausea
Worst in the days after each dose increase; usually settles as you adaptSmaller, more frequent meals rather than three large ones. Stop eating at the first sign of fullness rather than finishing the plate — on a GLP-1 the signal arrives later than the damage. Bland, low-fat food during flare-ups; fried and very rich meals are the most common trigger. Do not lie down straight after eating. If a dose increase causes nausea you cannot work around, ask about staying at the current dose longer rather than pushing through.
Constipation
Often builds over weeks rather than appearing suddenlyFluid and fibre first, and movement — a daily walk does more than people expect. Many clinicians are comfortable with an osmotic laxative or a stool softener used regularly rather than as a rescue; ask yours. This is the side effect most likely to end treatment quietly, so raise it early rather than enduring it.
Vomiting and diarrhoea
Usually dose-escalation relatedThe real risk here is dehydration, which can precipitate kidney injury. Keep fluids up deliberately. Persistent vomiting is not something to manage at home — contact your prescriber.
Fatigue and light-headedness
Common early, often under-recognisedFrequently under-eating rather than the drug itself. Appetite suppression makes it easy to fall well below what you need, particularly protein. If you feel weak or dizzy, look at intake before assuming it is a side effect to tolerate.
Injection-site reactions
Mild redness or itchingRotate sites — abdomen, thigh, upper arm — and do not inject into the same spot twice running. Let alcohol dry before injecting. Persistent, spreading or painful reactions are worth reporting.
Stop And Get Help
These are not side effects to manage at home. If any of the following happens, stop taking the medication and contact a clinician — or emergency services where indicated.
- ✕Severe, persistent abdominal pain, especially radiating to the back — possible pancreatitis. Stop the medication and seek care.
- ✕Pain in the upper right abdomen, fever, or yellowing of the skin or eyes — possible gallbladder disease.
- ✕Persistent vomiting with reduced urination — dehydration and possible kidney injury.
- ✕A lump or swelling in the neck, hoarseness, or trouble swallowing — report immediately given the thyroid C-cell warning.
- ✕Signs of a serious allergic reaction: swelling of the face, lips or throat, or difficulty breathing. Emergency care.
- ✕New or worsening depression, or any thoughts of self-harm — contact a clinician; in the US, call or text 988.
Two Things Most People Are Not Told
You are losing muscle as well as fat
The STEP 1 body-composition substudy found roughly 45% of total weight lost on semaglutide came from lean tissue; the SURMOUNT-1 substudy put it nearer 25% for tirzepatide. This is not a side effect in the usual sense — it is how the weight loss happens — but it has consequences for strength and long-term metabolic rate.
What the evidence supports as the countermeasure is resistance training specifically, not aerobic exercise, alongside protein commonly targeted at 1.2–1.6 g per kg of body weight per day during active loss. Hitting that while your appetite is suppressed takes planning. If you do one thing beyond taking the medication, make it this.
Delayed gastric emptying changes other things
These medications slow how quickly your stomach empties, and that has knock-on effects people are rarely warned about. Oral contraceptives can be absorbed less reliably — unintended pregnancy while on a GLP-1 is a genuinely common story, and these drugs should not be used in pregnancy. Alcohol tends to hit harder and differently. Other oral medications may absorb unpredictably, which matters most for drugs with a narrow therapeutic window.
It also matters before surgery: tell any anaesthetist that you take a GLP-1, because a stomach that has not emptied changes their planning. And avoid stacking anything else that slows the gut — opioid-receptor agonists such as kratom compound constipation by the same mechanism.
A note on titration
Almost every side effect on this page clusters around dose increases. The schedules used in the trials escalate slowly for exactly that reason. If a step up is intolerable, staying at your current dose for longer is a legitimate clinical option — not a failure, and not something you should have to argue for. A provider that pushes a fixed escalation schedule regardless of how you are doing is running a logistics operation rather than a clinical one, which is worth weighing when you choose one.
Keep reading
Medical Disclaimer: This page is for informational purposes only and does not constitute medical advice. Always consult a licensed healthcare provider before starting or changing any treatment. Compounded medications are not FDA-approved, are not evaluated by the FDA for safety, effectiveness or quality, and are not equivalent to the branded drug beyond sharing an active ingredient. GLP-1 medications commonly cause nausea, vomiting, diarrhoea and constipation, and carry risks including pancreatitis, gallbladder disease and kidney injury; they are contraindicated in people with a personal or family history of medullary thyroid carcinoma or MEN 2, and should not be used in pregnancy, when trying to conceive, or while breastfeeding. Prescribing is subject to clinician approval and is never guaranteed. Individual results vary and no outcome is promised.