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What this guide covers
Elke veelvoorkomende GLP-1-bijwerking, de week waarin ze meestal opduikt, waarom ze gebeurt en wat echt helpt. Met verwijzingen naar studiegegevens en bijsluiters. This is patient education, not a substitute for the prescriber who knows your case. Generic names sit next to brand names throughout: semaglutide (Ozempic, Wegovy), tirzepatide (Mounjaro, Zepbound).
Frequently asked questions
Which side effects are most common?
Across the STEP and SURMOUNT trial programs, the most commonly reported side effects for semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound) were gastrointestinal: nausea, diarrhea, constipation, vomiting, and abdominal pain. Most were described as mild to moderate and transient, with onset after the first dose or a dose increase and resolution within days to a few weeks. Serious adverse events were uncommon but included pancreatitis, gallbladder disease, and dehydration-related kidney issues.
Why do GLP-1s cause so much GI trouble?
The same mechanism that helps with weight and blood sugar also slows gastric emptying and acts on receptors in the brain's nausea pathway. Food sits in the stomach longer, which is why people feel full faster and why fatty or heavy meals can cause real discomfort. The FDA prescribing information for all four drugs names delayed gastric emptying as part of the mechanism. Most GI effects fade as the body adapts to each dose level.
What about muscle loss?
When anyone loses weight quickly, some of what they lose is lean mass. The STEP-1 body-composition substudy reported that participants on semaglutide lost roughly 39% of their lost weight as lean mass, a higher proportion than typical diet-only weight loss. The SURMOUNT-1 substudy reported closer to 25% for tirzepatide. What tends to move the needle: hitting a higher protein target (the literature on preserving muscle in a caloric deficit often points to 1.2-1.6g per kg body weight per day, per Phillips 2017) and doing resistance training 2-3 times per week.
What is 'Ozempic face'?
This is a media term, not a clinical one. It refers to the loss of facial volume that can happen with any meaningful weight loss: fat pads in the cheeks shrink, skin can look looser. It isn't specific to semaglutide; it happens with surgical weight loss and significant diet-based loss too. There's no published trial data quantifying it specifically for GLP-1s. What patients report trying: slower weight loss, adequate protein, and a dermatology consultation.
What about hair thinning?
Hair shedding during significant weight loss is well-documented across diet, surgery, and now GLP-1 populations. It's usually telogen effluvium: a temporary shift in the hair-growth cycle triggered by the physiologic stress of rapid weight change or caloric restriction. The STEP and SURMOUNT trials reported alopecia at rates higher than placebo but low in absolute terms. It tends to show up 2-4 months after major change and usually resolves within 6-9 months. Protein adequacy and iron checks are the standard workup.
When should I call my doctor?
The FDA labels flag several things worth a prompt call: severe or persistent abdominal pain (especially if it radiates to the back, a possible pancreatitis signal), signs of gallbladder disease (right-upper-abdomen pain, fever, yellowing of the skin), severe vomiting that prevents keeping fluids down, signs of dehydration (dark urine, dizziness), vision changes (a diabetic retinopathy signal in people with diabetes), and any suicidal thoughts. The prescribing information lists these explicitly. If something scares you, it's worth a call.
Do side effects get better over time?
The trial data says yes for most people. In the STEP-1 publication, the proportion of participants experiencing GI events declined across the 68-week trial, with most events clustering around dose increases and resolving within 1-2 weeks. A minority of participants (roughly 5-7% across these trials) discontinued due to GI side effects, which means the majority found them manageable and fading. If yours are getting worse instead of better past week 3 of a dose, that's the signal to loop in your prescriber.
Sources
Related reading
Ozempic Constipation: What Helps, Plus the Best Fiber Supplements
Yes, Ozempic and other GLP-1s commonly cause constipation, here's why it happens, how long it usually lasts, and what actually relieves it, including which fiber to buy and which to skip.
Ozempic Week by Week: What to Expect
A week-by-week timeline of the first year on semaglutide. What is normal. What is not. When to call your doctor.
Best Electrolytes for GLP-1 Users (and Ozempic Fatigue)
When appetite drops on a GLP-1, sodium, potassium, and magnesium drop with it, and that shortfall is behind a lot of the first-month fatigue. Here's what's worth buying, what to skip, and which formulas are calm on the stomach.