Starting a GLP-1 medication is a bit like the first week at a new gym — your body needs time to adjust, and the adjustment period isn't always comfortable. Most people experience some side effects in the first few weeks, and knowing what's coming makes it a lot easier to push through.
The Most Common Side Effect: Nausea
Nausea is the big one. Somewhere between 20-40% of patients on semaglutide or tirzepatide report it, and it usually hits hardest in the first two to four weeks or after a dose increase. For most people, it's mild to moderate — not debilitating, but annoying enough that you'll notice it.
A few things that help: eat smaller meals, avoid greasy or heavy foods, and don't lie down right after eating. Some providers will prescribe anti-nausea medication (ondansetron is common) if it's interfering with your daily life. Ginger tea and peppermint actually do help for a lot of people — it's not just folk medicine.
Digestive Changes
GLP-1 medications slow gastric emptying, which is part of how they reduce appetite. The trade-off is that your digestive system needs to recalibrate. Expect some combination of:
- Decreased appetite — this is the intended effect, but it can feel strange at first
- Constipation — very common, especially in the first month. Stay hydrated and consider a fiber supplement
- Diarrhea — some people get the opposite. It usually settles within a week or two
- Bloating or gas — tends to improve as your body adapts
The appetite suppression can be surprisingly strong early on. Some patients say they simply forget to eat, which sounds great until you realize you still need adequate nutrition. Aim for protein-rich meals even when you're not hungry. Your provider should discuss dietary adjustments that work well with GLP-1 medications.
Fatigue and Headaches
Feeling tired or getting headaches in the first week or two is pretty standard. Part of this is your body adjusting to the medication, and part of it is that you're eating fewer calories than before. Make sure you're drinking enough water — dehydration makes both symptoms worse. Most people find the fatigue lifts after the first couple of weeks.
Injection Site Reactions
These are usually minor: a little redness, mild itching, or slight swelling at the injection site. Rotating where you inject (abdomen, thigh, or upper arm) helps prevent this. The needles on modern GLP-1 pens are thin enough that most people barely feel them.
When to Call Your Doctor
Most side effects are temporary and manageable. But contact your provider right away if you experience severe abdominal pain that doesn't go away (this could indicate pancreatitis, which is rare but serious), persistent vomiting where you can't keep fluids down, or signs of an allergic reaction like swelling of the face or difficulty breathing.
The good news: side effects almost always improve with time. The standard dosing schedule starts low and increases gradually for exactly this reason. If a dose increase hits you hard, your doctor may keep you at the current dose longer before moving up.
Talking to an experienced provider makes a real difference in managing this transition. Find a GLP-1 clinic near you to discuss what to expect, or read about what happens at your first appointment. If you're weighing medication options, see how Ozempic and Wegovy compare in terms of side effect profiles.