GLP-1 side effects: What to know 

Starting a GLP-1 comes with a lot of curiosity — and usually a few questions, too.

What will it feel like? Will your body react right away? And what, exactly, counts as “normal”?

But like most medications, they can come with side effects — especially as your body gets used to it. The good news is that many of these changes are manageable, and knowing what to expect can make the experience feel a lot less uncertain.

Vidhi Shah, M.D., an internal medicine physician with Sutter, says “Mild side effects can happen as your body adjusts to GLP-1 medications —  but the health risks of untreated obesity are far more serious. You don't have to navigate these alone. With a personalized plan and support, most side effects can be managed easily.”  

Understanding how side effects show up — and what they might be telling you — can help you stay ahead of symptoms and have more informed conversations with your care team.

GLP-1 receptor agonists

You may recognize GLP-1 medications by their brand names, such as semaglutide (Ozempic, Wegovy) or tirzepatide (Mounjaro, Zepbound).

These medications mimic a natural hormone your body already makes. That hormone helps regulate blood sugar, support insulin function and signal fullness after you eat.

Because of how they work, GLP-1s are commonly used to manage Type 2 diabetes and support weight management. When paired with lifestyle changes, they can help regulate blood sugar and support sustainable weight loss.

Some people may see meaningful weight changes over time — especially when medication is combined with nutrition, movement and other healthy habits. 

Most common GLP-1 side effects

If side effects show up, they’re most often related to digestion. You might notice:

• Abdominal pain
• Bloating
• Constipation
• Diarrhea
• Indigestion
• Nausea or vomiting

Other possible side effects include fatigue, headache or mild irritation at the injection site.

For many people, these symptoms are temporary. They’re most likely to appear when you first start the medication or after a dose increase — times when your body is still getting used to the change.

If something feels off or harder to manage, you don’t have to figure it out on your own. Your provider can help adjust your plan. Starting at a lower dose and increasing gradually is one common way to ease the transition. 

GLP-1 long-term side effects

One of the more noticeable changes can be a reduced appetite or feeling full sooner than usual. That’s part of how these medications work — but it can also make it easier to unintentionally eat too little.

Over time, that shift may increase the risk of:

• Dehydration
• Muscle loss
• Nutrient deficiencies

A few small, consistent habits can help support your body while you’re on a GLP-1:

• Include enough protein each day to help maintain muscle
• Add strength training, if it fits your routine
• Choose a variety of fruits and vegetables for key nutrients
• Try smaller, balanced meals throughout the day
• Stay hydrated, even if you’re not feeling thirsty

Your care team can help tailor these choices to your needs, your routine and your goals. 

Serious but rare side effects

Serious side effects are uncommon, but it’s still important to know what to watch for. These can include delayed stomach emptying (gastroparesis), bowel obstruction and kidney problems.

Eating smaller meals and staying hydrated may help lower your risk.

You might also be wondering about a possible link between GLP-1 medications and cancer. Current research hasn’t shown a clear connection to thyroid cancer in humans, though this is still being studied.

Shah says, “Side effects are common with all medications — including over-the-counter drugs. Medications receive FDA approval not because they’re free of side effects, but because their expected benefits outweigh the risk of serious adverse effects. For that reason, I recommend using only FDA-approved GLP-1 medications under the guidance of a healthcare professional.”

If you notice new or worsening symptoms — or if something just doesn’t feel right — check in with your clinician. They can help you understand what’s expected, what’s not and what next steps might make sense for you.