If you're starting (or considering) a GLP-1 medication like semaglutide or tirzepatide, this is the article we wish every patient read first. Because here's the truth: most side effects are mild and temporary, and most of the worst stories come from people who didn't have a plan.
This guide will walk you through what's normal, what's not, and what you can actually do about it, in plain language, without scaring you.
The Big Picture
In the STEP trials for semaglutide and the SURMOUNT trials for tirzepatide, the most common side effects were gastrointestinal: nausea, constipation, diarrhea, and stomach upset. The vast majority were mild to moderate and improved as the body adjusted.
Across these large trials, fewer than 7% of patients stopped semaglutide because of side effects (Wilding et al., NEJM 2021). That means more than 9 out of 10 people tolerated it well enough to keep going.
Knowing what to expect, and how to handle it, makes a huge difference.
The Most Common Side Effects
### 1. Nausea
What it feels like: A queasy, "ate too much" feeling, often after meals. Usually worst in the first week or two of a new dose.
Why it happens: Semaglutide and tirzepatide slow how quickly your stomach empties. Food sits longer. Combine that with eating the same portions you used to, and your stomach feels overfull.
*What helps:*
When to call your clinician: Nausea that doesn't let up after 2 weeks at a dose, or that prevents you from keeping fluids down.
### 2. Constipation
What it feels like: Going less often, harder stools, more straining.
Why it happens: Slower digestion + often eating less + sometimes drinking less = backed-up plumbing.
*What helps:*
When to call your clinician: No bowel movement in 4–5 days despite the above, or significant abdominal pain.
### 3. Diarrhea
What it feels like: Looser, more frequent stools, often after fatty meals.
Why it happens: GLP-1s change how your gut handles fats and bile.
*What helps:*
When to call your clinician: Severe diarrhea, signs of dehydration, blood in stool, or symptoms lasting more than a few days.
### 4. Reflux and Burping
Common, usually mild. Eat smaller meals, avoid eating within 2–3 hours of bed, and consider an OTC antacid as needed.
### 5. Fatigue
Some patients feel tired in the first week or two, often because they're eating dramatically less. Make sure you're getting:
If fatigue is severe or persistent, get labs checked (iron, B12, thyroid).
### 6. "Sulfur Burps"
A few patients get burps that smell like rotten eggs, often paired with stomach upset. It's harmless but unpleasant. Smaller, lighter meals usually fix it. Some find that activated charcoal capsules help (ask your clinician).
### 7. Headache
Often dehydration or low blood sugar in disguise. Drink water, add a pinch of salt, eat a small protein-containing snack.
### 8. Injection Site Reactions
Some redness, itching, or a small bump where you inject is normal and usually fades within a day. Rotate injection sites (abdomen, thigh, back of upper arm) and use a fresh needle every time.
Less Common but Important to Know
### Gallbladder Issues
Rapid weight loss of any kind, diet, surgery, medication, can increase gallstone risk. Symptoms include sharp pain in the upper right abdomen (often after fatty meals), nausea, and pain that radiates to the right shoulder. Call your clinician right away.
### Pancreatitis
Rare but serious. Symptoms: severe, persistent upper abdominal pain (often radiating to the back), nausea, vomiting. This needs immediate medical attention.
### Hair Thinning
Mostly related to rapid weight loss, not the medication itself. Adequate protein, biotin, iron, and slow steady weight loss help. Hair usually rebounds once weight stabilizes.
### Mood Changes
Some patients report low mood or anxiety, especially during dose changes. If you notice this, talk to your clinician, don't power through it.
### Hypoglycemia (Low Blood Sugar)
Mostly a concern for patients with diabetes on other medications. Eating regular small meals with protein helps prevent it.
Side Effects That Mean Stop and Call Now
Reach out to your clinician immediately (or seek emergency care) if you have:
These are uncommon, but they're situations where speed matters.
How to Set Yourself Up for Success
### 1. Trust the Slow Titration
The starter doses (0.25 mg semaglutide, 2.5 mg tirzepatide) feel small, and patients sometimes pressure their clinician to "just go faster." Don't. The slow ramp-up is the single best predictor of tolerability.
### 2. Re-Learn Your Hunger
Pre-GLP-1, many of us ate by clock and habit. On a GLP-1, your body is finally giving you accurate fullness signals. Listen to them. Stop when satisfied. Save leftovers without guilt.
### 3. Front-Load Protein
Aim for 25–40g protein at breakfast and lunch. Protein protects muscle as you lose weight and keeps you stable.
### 4. Hydrate Like It's Your Job
Most "side effects" people complain about are actually dehydration. A simple test: pee should be pale yellow. Add electrolytes if you're sweating, in heat, or eating low-carb.
### 5. Move Your Body
Even a daily 20–30 minute walk dramatically reduces side effects. Strength training 2–3x/week protects your muscle and metabolism.
### 6. Plan for Bad Days
Have ginger ale, broth, electrolyte powder, crackers, and rice on hand. Knowing you have a "rough day kit" makes the rough days feel manageable.
### 7. Stay in Touch with Your Clinician
The number-one thing patients say after a successful first 6 months on GLP-1: "I'm so glad I had someone to message when something felt off." This is what real telehealth care looks like, not just a prescription, but a partnership.
The Honest Takeaway
GLP-1 medications are powerful, well-studied, and life-changing for many people. They also come with side effects, most mild, most temporary, almost all manageable.
If you go in informed, paired with a real clinician, with a plan for the first 8 weeks, your odds of a smooth journey are very high.
Take our free 2-minute assessment to see if a GLP-1 program from Majesta Health is right for you. Every patient gets a licensed clinician, real human support, and a clear plan from day one.
Take the free 2-minute assessment →
This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider. Results may vary.