Weight Loss

GLP-1 Side Effects: What to Expect When Starting Wegovy, Ozempic, Mounjaro, or Zepbound

By Dr. Rachel Gougian, DO, FAAFP, D-ABOM

Updated September 2026

GLP-1 medications have changed how we approach weight loss in clinical practice. Wegovy, Ozempic, Mounjaro, and Zepbound are all effective tools, and they all come with side effects that are worth understanding before you start.

Most side effects are temporary and manageable. A few are serious enough to warrant a real conversation with your doctor. This guide covers what the research actually shows, what I see in my own practice, and what you can do to make the adjustment period easier.

If you are considering one of these medications or have already been prescribed one, this is meant to help you feel prepared rather than surprised.

GLP-1 medications work by mimicking a hormone your body already produces. They slow gastric emptying, reduce appetite, and affect how your brain processes hunger signals. Because they change how your digestive system operates, most side effects involve the GI tract.

Nausea

This is the single most reported side effect across all four medications. It tends to be most noticeable right after a dose increase and usually settles within one to two weeks at each new level. In clinical trials, roughly 40 to 45 percent of patients on semaglutide (Wegovy and Ozempic) reported nausea at some point during treatment. For tirzepatide (Mounjaro and Zepbound), the numbers are similar.

Eating smaller meals throughout the day helps significantly. Avoiding greasy or heavy foods during the first week after a dose increase makes a noticeable difference for most patients. Staying upright after eating, rather than lying down, also reduces the sensation.

Constipation

Because GLP-1 medications slow the movement of food through your digestive tract, constipation is common. This catches some patients off guard because it is not always discussed in the same breath as nausea, but in my practice it is one of the most frequent complaints.

Increasing water intake and fiber early on, ideally before you even start the medication, makes a real difference. If dietary changes are not enough, we can discuss adding a stool softener or mild laxative. This is not something you should just tolerate quietly.

Diarrhea

Some patients experience the opposite of constipation, particularly during the first few weeks. Loose stools and diarrhea tend to resolve as your body adjusts to the medication. If it persists beyond a few weeks, it is worth discussing at your next visit.

Fatigue

Some patients feel more tired than usual, especially in the first month. This is partly related to reduced calorie intake and partly to the medication itself. It usually passes as your body adapts. If fatigue is significant enough to affect your daily life, let your doctor know. Sometimes adjusting the titration schedule helps.

Decreased appetite

This is technically the intended effect, but it can feel more dramatic than expected. Some patients describe simply forgetting to eat or feeling full after a few bites. This is normal and actually a sign the medication is working. The important thing is to continue eating regular, nutritious meals even when you do not feel particularly hungry. Skipping meals entirely can lead to muscle loss and nutrient deficiencies over time.

Every GLP-1 medication starts at a low dose and gradually increases over several weeks or months. This is called titration, and it exists specifically to give your body time to adjust. Rushing through titration is one of the biggest reasons patients have a hard time with side effects.

For semaglutide medications like Wegovy and Ozempic, the standard titration takes about four to five months to reach the full dose. Tirzepatide medications like Mounjaro and Zepbound follow a similar gradual schedule.

At Pandora Family Medicine, I sometimes slow the titration down further if a patient is having a rough time at a particular dose. There is no medical reason to push through severe side effects just to get to the target dose faster. The goal is sustainable treatment, not speed.

This is one of the things that makes physician-guided treatment different from an app or subscription service. When your doctor knows you and sees how you are responding, the plan can change in real time.

The serious risks associated with GLP-1 medications are rare, but they are real and deserve a straightforward discussion.

Pancreatitis. There have been reports of acute pancreatitis in patients taking GLP-1 medications. Symptoms include severe abdominal pain that radiates to the back, often accompanied by nausea and vomiting. If you experience this kind of pain, stop the medication and contact your doctor or go to the emergency room. This is not a wait-and-see situation.

Thyroid tumors. In animal studies, GLP-1 receptor agonists caused thyroid C-cell tumors in rodents. It is not clear whether this translates to humans, but as a precaution, these medications carry a boxed warning and are not recommended for patients with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2.

Gallbladder issues. Rapid weight loss from any cause increases the risk of gallstones. GLP-1 medications are no exception. If you develop sharp pain in the upper right side of your abdomen, especially after eating, let your doctor know.

Kidney problems. Severe nausea, vomiting, or diarrhea can lead to dehydration, which can affect kidney function. Staying hydrated is important for general health, but it is especially important while taking these medications. Patients with pre-existing kidney disease should be monitored more closely.

Most GLP-1 side effects are uncomfortable but not dangerous. However, you should contact your doctor if you experience any of the following:

• Severe abdominal pain that does not go away
• Persistent vomiting that prevents you from keeping food or liquids down
• Signs of dehydration, including dark urine, dizziness, or rapid heartbeat
• A lump or swelling in your neck
• Vision changes
• Yellowing of the skin or eyes

At Pandora Family Medicine, follow-up care is built into how we manage weight loss. You are not left to figure out side effects on your own. When something feels off, we want to hear about it so we can adjust your plan.

Starting a GLP-1 medication is not just about writing a prescription. At your initial visit, we review your medical history, run labs, and talk honestly about what to expect. That conversation includes side effects, because being prepared makes a meaningful difference in how well patients tolerate the transition.

We also build follow-up visits into your treatment plan. These are not optional add-ons. They are how we track your progress, adjust doses, monitor labs, and address side effects before they become reasons to stop treatment altogether.

The initial weight loss visit at Pandora Family Medicine is $200. Follow-up visits are $150. There is no subscription, no monthly platform fee, and no mandatory program enrollment. You see the same doctor every visit, and that doctor is a board-certified obesity medicine specialist who can adjust your plan based on how your body is actually responding.

If you are thinking about starting a GLP-1 medication, or if you have already started and are struggling with side effects, we are here to help.