GLP-1 Medications and Fatigue: Possible Causes and What to Discuss

Fatigue is a reported side effect of GLP-1 medications, but it can have several overlapping causes. Eating and drinking less during treatment may play a part, as can rapid weight loss, nutrition gaps, sleep problems, or other health conditions. The available figures show that fatigue affects some people in clinical trials; they don’t explain why a particular person feels tired or establish that the medication is the only cause.

What research says about fatigue

In clinical trials, about 11 percent of adults taking Wegovy reported fatigue or weakness, compared with 5 percent of those taking a placebo. For Zepbound, fatigue was reported by 5 to 7 percent of participants, depending on dose, compared with 3 percent taking a placebo. These results suggest the symptom is more common with the medications in those trials, while also showing that some people in the comparison groups reported it.

A separate analysis used artificial intelligence to review more than 410,000 Reddit posts from people taking semaglutide or tirzepatide. About one in six users mentioned fatigue, making it the second most common complaint after nausea in that analysis. Social media posts can capture experiences that trial reports may miss, but they can’t tell us how common fatigue is among all people taking these medicines: people who post online may not represent the wider group, and a post can’t establish what caused a symptom.

When fatigue may show up

Yuval Pinto, MD, an obesity and family medicine physician at Johns Hopkins Medicine, says he often sees fatigue during periods of faster weight loss, when a person’s body is adapting to eating less. He reports that it may last two or three months for some patients before improving. That’s a clinician’s observation, not a fixed timeline or a guarantee that fatigue will resolve on its own. Fatigue that persists beyond an adjustment period may have another explanation worth exploring.

GLP-1 medicines can slow the movement of food through the stomach, helping people feel full sooner. That effect may mean fewer calories and less fluid from food. If someone’s intake drops too far, the body may not get enough energy or nutrients to support daily activity. A smaller appetite can also make it harder to notice hunger or thirst cues.

Several factors can add up

Low fluid intake is one possible contributor. Dehydration is associated with fatigue, and people may drink less if their thirst cues change or they’re eating less. Food provides some of the fluid people need, so a reduction in meals can also reduce that source.

Nutrition gaps are another possibility. Eating substantially less can make it harder to get enough protein, carbohydrates, fats, vitamins, and minerals. Vitamin D deficiency may also contribute to tiredness; Pinto notes that some people with obesity already have low vitamin D levels. These possibilities don’t mean a supplement is needed: a clinician can help assess whether a deficiency or another cause is present.

Weight loss can also affect thyroid medication needs. Pinto says that doses may need review as a person’s weight changes, whether or not the weight loss is linked to a GLP-1. People with diabetes may experience fatigue related to diabetes itself. For those also taking insulin or a sulfonylurea, low blood sugar is another possible concern to discuss with a clinician.

Everyday steps to consider

For some people, planning smaller, balanced meals can make it easier to eat regularly when large portions are unappealing. Susan Swafford, MPH, RD, a clinical dietitian at the Duke Lifestyle and Weight Management Center, describes meals with lean protein, vegetables, fruit, and whole grains as one approach. Pinto suggests paying attention to whether energy changes when meals are more regular, while respecting a lack of appetite rather than forcing food.

When portions are small, choosing foods with a range of nutrients may help people make more of what they do eat. Smoothies or protein drinks made with fruit, vegetables, and unsweetened milk or yogurt may be easier to manage than heavier foods for some people; cottage cheese and soups are other options mentioned by the dietitian.

Protein deserves attention during weight loss because inadequate intake over time can contribute to muscle loss, which may affect strength and energy. Swafford says many people she sees while taking GLP-1 medicines eat only one or two meals a day and may not get enough protein. She describes a general target of about 70 to 100 grams daily for most people and suggests spreading intake across at least three meals, since the body absorbs only about 20 to 30 grams at a time. Individual needs vary, so these figures are useful context rather than a personal prescription.

Strength training can help protect muscle during weight loss, and regular movement may support energy. Swafford points to studies in which adequate protein and regular strength training were both part of preventing muscle loss. A walk outdoors is another accessible form of activity, if it’s appropriate for a person’s health and abilities.

Hydration needs vary. Swafford offers nearly clear urine as a rough guide, while noting that vitamins can affect urine color. She cites at least 48 ounces of fluid a day for many people, with taller people sometimes needing 80 to 100 ounces. These amounts aren’t a universal target; health conditions can change fluid needs. She suggests reserving electrolyte drinks for heavy sweating, workouts lasting longer than an hour, or recovery after vomiting or diarrhea.

Sleep matters, too. A disrupted sleep schedule can leave someone tired, and sleep disorders such as obstructive sleep apnea can cause repeated awakenings. People with symptoms or a known sleep disorder can ask a clinician about evaluation and treatment. Weight loss may improve sleep apnea symptoms for some people; the source also notes that Zepbound has received approval for this disorder.

When to contact a clinician

Contact a healthcare provider about fatigue that is consistent, worsening, or debilitating. Pinto also advises prompt contact if fatigue is so severe that someone can’t get out of bed or is falling asleep while driving, or if it comes with extreme loss of appetite, thoughts of suicide, very long or heavy menstrual periods, or blood in the toilet. These symptoms deserve individual assessment rather than an assumption that the medication explains them.

If appetite is so low that adequate food intake seems difficult, Swafford says a lower dose may be worth discussing with the prescribing clinician. Don’t change a dose on your own. A clinician can review medication, intake, weight changes, sleep, and other possible causes together, which is especially useful when fatigue doesn’t ease or is interfering with daily life.