Yes, your GLP-1 could be making you tired

People starting on a GLP-1 might expect GI side effects like nausea and constipation — but there’s another very real side effect that flies a little more under the radar: GLP-1 fatigue. GLP-1 medications like Ozempic and Mounjaro (for type 2 diabetes) and Wegovy and Zepbound (for weight loss) might leave you feeling more tired than usual, but it’s not because of anything they’re doing directly in the body. Rather, there’s a domino effect happening: You eat less on a GLP-1, which means you may not be getting the fuel you need to stay energized. The good news? It’s entirely possible to close this energy gap with a few tweaks to your diet.

Key takeaways:

• GLP-1s can indirectly cause fatigue by reducing the amount of fuel you get from food.

• GI side effects, like nausea, diarrhea, and vomiting, can lead to dehydration and loss of electrolytes, making you tired as well.

• To offset it, make sure you’re eating enough protein and fiber, and sip water throughout the day to stay hydrated.

• Regular movement and good sleep hygiene can also help fend off fatigue.

• GLP-1 fatigue should ease up over time, but if not, you can talk to your doctor about adjusting your dose.

Although less common than GI-related GLP-1 side effects like constipation, diarrhea, and nausea, feeling tired can definitely happen when taking a GLP-1. “Fatigue can happen when doses are initiated or escalated,” says Dr. Holly Lofton, M.D., a board-certified obesity medicine specialist at NYU Langone Health. That’s because with each subsequent uptick in your dose, the effects get more intense. 

GLP-1 medications work by mimicking GLP-1, a hormone your body releases when you eat. The meds help you feel full longer, reduce your appetite, and stabilize your blood sugar after a meal. As a result, your appetite and subsequent food intake may decrease more and more with each dose — creating a perfect storm for fatigue.

You might have less fuel in terms of blood sugar, but you might also be lacking fuel in terms of calories, too. “Because the medication induces satiety, it makes people feel fuller sooner — so they're just not eating as much, and they might not be getting the nutrition their body needs,” says Dr. Juliana Simonetti, M.D., a board-certified internist at University of Utah Health and co-director of its Comprehensive Weight Management Program. Here’s a closer look at what’s going on.

You’re probably eating a lot less

For one, if you’re eating less overall, then it’s reasonable to assume that your calorie intake is going to go down, too. There's not a whole lot of evidence to compare how many fewer calories you eat when you're on a GLP-1 versus not, but one study did find that people taking semaglutide ate about 35% fewer calories at an all-you-can-eat lunch compared to those not on a GLP-1.

You could not be getting enough protein

Some studies have found that when your overall calories drop while on a GLP-1, you’re less likely to get all the protein you need. If you’re suddenly not feeling very hungry, an apple for a snack or a few crackers might do the trick. The same goes for your meals: Maybe you’re satisfied with a salad or a slice of pizza when before you used to eat an entire burger. This can help you lose weight, but it can also put a dent in your protein intake, which provides the body with steady energy throughout the day. 

You may be dehydrated

Your fatigue could be the work of dehydration, which can happen for a few reasons. For one thing, you might be less inclined to drink a glass of water if you already feel stuffed at mealtime. Dehydration can also arise from some of the other side effects of GLP-1s — namely, nausea, vomiting, and diarrhea. Vomiting and diarrhea can also contribute to an imbalance in electrolytes, like sodium, potassium, and magnesium, and together, the combination can make you feel sluggish and tired.

Your blood sugar can dip

If you go for hours between eating because you’re just not hungry, your blood sugar levels might get low. That doesn’t necessarily lead to hypoglycemia, or low blood sugar, but less glucose does mean less energy for your cells. Glucose is a fuel source for your body; when there's not enough circulating in your bloodstream, it's harder for your brain and muscles to get the energy needed to function properly. “Since you are essentially running on less ‘fuel’ than you are used to, it can make you feel fatigued,” Lofton says.

Your B12 and iron levels might be low

There's emerging evidence to show that people on GLP-1s tend to experience a loss in iron levels; one small study found that after 10 weeks, nearly two in five participants taking semaglutide experienced a 30%-plus reduction in iron absorption. Researchers are still figuring out if this is because of a dietary change, weight loss, or the effects of the drug on iron absorption. Also, if you're not eating enough protein, you might be short on vitamin B12 — which is primarily found in animal products, such as red meat and eggs. If you’re feeling fatigued, you could get your levels of B12 and iron checked to see if they are low.

You may not be sleeping enough

A lot of Americans already have poor sleep due to staying up late and scrolling on their phones close to bedtime, and adding a GLP-1 on top of those habits can take things from bad to worse. After all, if you’re feeling uncomfortable from constipation or feel too queasy from nausea to fall asleep, you’re going to feel exhausted the next morning.

Here’s what you can tweak in order to get more energized while taking a GLP-1.

Don’t skip meals

It can be easy to forget to eat when your appetite is low, but try not to go too long without eating. Ideally, you shouldn’t go more than three to four hours without eating, says Simonetti, who recommends adding in a healthy snack if that helps you get to that frequency. Even something like a protein shake can help give you calories when you don’t want to sit down for a full meal.

Prioritize protein

When you do eat, make sure you’re getting protein in every meal — think eggs, cottage cheese, yogurt, and lean meats like chicken, fish, and turkey, says Simonetti. Ideally, you should aim for at least 1 gram per kilogram of body weight a day when losing weight on a GLP-1. It’s a good idea to incorporate protein into your snacks, too: “You can have almonds, yogurt, or cottage cheese with a little bit of fruit,” Simonetti says.

Include steady-energy carbs and fiber

Carbohydrates are your body’s primary energy source — but it’s important to choose your carbs wisely. Ideally, they should offer more than 5 grams of fiber per serving, says Lofton. You should also aim for carbs that aren’t refined, like whole grains or fruits and vegetables; these can provide what’s known as steady-state fiber, meaning they help provide constant energy.

On the flip side, simple carbs — like pasta, white rice, and white bread — can give you a quick burst of energy but it won’t last. Plus they “make you feel full sooner without giving you as much nutrition,” says Simonetti. 

Hydrate and replace electrolytes

Your hydration needs can vary based on your age, weight, activity levels, and other factors. But it's easy enough to tell if you're drinking enough water: Just look at your urine. If it's pale yellow, you're all good. Any darker and you might need to drink a little more. Try sipping on water throughout the day (instead of chugging a glass or two in one sitting), and make sure you're eating water-dense fruits and vegetables like celery, bell peppers, citrus fruits, melons, and berries.

As for electrolytes, you only really need them if you’re doing an intense workout (and sweating accordingly) or have experienced GI issues like vomiting or diarrhea, which can cause an imbalance. If that’s the case, you can re-up on electrolytes with fruits and vegetables — think bananas for potassium, or leafy greens like spinach for potassium and magnesium — or add an electrolyte powder to your water.

Don’t skimp on iron and B12

Both iron and B12 deficiencies can cause fatigue, so make sure you’re getting enough. You can get iron from beans, eggs, and proteins — think lean red meat, poultry, and fish like salmon and tuna. Vitamin B12, meanwhile, is easily available in most animal protein sources, like eggs and meat.

You may also want to consider a supplement. “There are consensus guidelines that recommend patients take a multivitamin when taking GLP-1s, because they’re less likely to get vitamins from their nutrition alone,” says Simonetti. If you try a multivitamin or supplement (ideally with your doctor’s okay) and don’t feel any improvement, then you can get your levels tested to see if you have a true deficiency.

Being active during the day — particularly in the morning — can help you feel ready for bed and reset your circadian rhythm so that you’re tired and awake at the right moments of the day. And remember: Sleeping seven to nine hours a night is right for most adults. If you aren’t getting enough, think about how you can get more. You may need to stop looking at your phone in bed, tweak your coffee intake, or stop sleeping in on the weekends.

If your fatigue is preventing you from doing things you normally do, then it’s worth talking to your doctor about it. The same goes if the G.I. side effects of a GLP-1 are interfering with your sleep, since your provider can help you troubleshoot. If the fatigue doesn’t get better after a few months at the same dose of your GLP-1, mention it to your doctor so you can rule out other issues. They may recommend slowing the dose escalation or even decreasing the dose, says Lofton.

When you’re eating less, you have to make every meal count. That can help ensure you get the fuel you need while minimizing side effects. And the GLP-1 Success Program can be the ace in your pocket: 73% of Weight Watchers Med+ members given the GLP-1 Success Program said it helped minimize their side effects.* It does this by helping you build the healthy habits you need to not only help maximize your results on a GLP-1, but feel your best, too.

GLP-1s effectively work by reducing your appetite and extending feelings of fullness so you ultimately eat less — but that can mean you’re not getting all the fuel you need to feel refreshed and ready for the day. On top of that, the more common GI side effects, like nausea and vomiting, can impact your energy in their own right by wrecking your sleep and causing dehydration. By eating three full meals with a balance of protein and fiber, as well as staying on top of your water intake, you can get the nutrients you need and shake off the fatigue. Weight Watchers can help you keep those healthy habits front of mind and support you in hitting your daily goals. And when in doubt, talk about your GLP-1 fatigue with your clinician.