Are weight loss injections safe?

Types of weight loss injections

The two main GLP-1 medications that are approved by the U.S. Food and Drug Administration (FDA) are semaglutide and tirzepatide.

• Semaglutide, marketed under the brand name Ozempic, is FDA-approved for diabetes, while Wegovy is the brand name approved for weight loss only.
• Tirzepatide is marketed under the brand name Mounjaro for type 2 diabetes, and Zepbound is the brand name approved for weight loss.

Despite their popularity, weight loss injections like GLP-1 medications aren’t just a fast and easy way to lose a few pounds.

“GLP-1s like semaglutide and tirzepatide have been marketed with dramatic before-and-after stories, celebrity endorsements and headlines focusing on rapid weight loss. This simplifies a complex therapy into a ‘quick fix’ narrative,” explains Paunel Vukasinov, MD, a dual board-certified internist and obesity medicine specialist, with Medical Offices of Manhattan in New York.

Vukasinov says a lot of people misunderstand that GLP-1 medications were originally used for managing type 2 diabetes and are now prescribed for obesity as part of a whole-body treatment plan. That includes lifestyle changes and a medical provider overseeing treatment.

Side effects of weight loss injections

Common side effects of weight loss injections include gastrointestinal (GI) symptoms like nausea, vomiting and diarrhea, particularly when you first begin treatment or increase your dose. You might notice other side effects like dizziness, headaches and injection-site reactions. Vukasinov notes that early in treatment, many people also report low energy levels.

Other side effects that some people experience aren’t necessarily due to GLP-1s themselves, but from rapid weight loss, according to Vukasinov. He says hair loss, which some people report happened after starting GLP-1s, might be from underlying stress or nutritional deficiencies, especially protein, zinc, iron and B12. “[Hair loss] is commonly seen with bariatric surgery and other rapid weight loss methods too,” he adds.

Benefits of weight loss injections

Weight loss injections can help people lose more weight than with other methods of weight loss, including lifestyle changes alone. And weight loss medications in general, including pills, along with lifestyle changes, can help you lose between 3% and 12% of your body weight, according to research.

Vukasinov also says the benefits extend into more than weight loss and blood sugar control to include:

• Reduced risk of heart attack or stroke, especially in people with type 2 diabetes or heart disease
• Lower blood pressure
• Improved cholesterol and triglyceride levels
• Lower inflammation levels in the body
• Improving fatty liver disease
• Regulating appetite and potentially helping with food cravings or addictions

GLP-1 medications can help you lose weight in the short term. Zepbound has been the most successful in weight loss, with people losing about 21% of their body weight when taking the highest dose. But one study looked at people who stopped taking semaglutide and found they had gained back about 21 pounds over the course of a year.

Long-term safety with weight loss injections

Vukasinov says taking GLP-1 medications long-term brings a few health risks, but they’re rare.

• Pancreatitis and gallbladder disease: Pancreatitis is when the pancreas becomes inflamed, while gallbladder disease can include inflammation and gallstones. These risks are small, but they can be serious if they happen, says Vukasinov.
• Thyroid C-cell hyperplasia: This is a condition where abnormal thyroid cells can lead to medullary thyroid cancer. But Vukasinov says there hasn’t been any confirmed link between GLP-1 use and thyroid cancer in humans, just in rodent studies. Still, it's something your health care provider may monitor for.

As of yet, there hasn’t been evidence that suggests long-term health problems when GLP-1 medications are appropriately prescribed and monitored, according to Vukasinov.

In fact, the SELECT trial for people taking semaglutide for weight loss actually showed benefits to the heart, such as a lower risk of a heart attack or stroke than the placebo group. “We’re getting longer-term data, but ongoing monitoring is essential,” Vukasinov says.

Some lifestyle factors contribute to weight loss injection risk

Your lifestyle choices can affect how well the medication is working for you, as well as its safety, according to Vukasinov. High-fat meals and alcohol use can make GI side effects like nausea, vomiting and reflux worse. Alcohol can also increase the risk of pancreatitis, says Vukasinov.

One 2025 study in the journal Obesity Reviews suggested that those who took semaglutide and tirzepatide during clinical trials lost 10% or more of their muscle mass over the 68 to 72-week period. That was equal to about 20 years of muscle loss that naturally happens due to age.

Vukasinov also says eating an unhealthy diet or one low in protein can increase the risk of lean muscle mass loss and nutrient deficiencies. Losing lean muscle mass can also happen if you’re not doing enough resistance training and getting enough protein in your diet while on GLP-1 medications.

Working with your health care provider for long-term success

To help you be successful with weight loss, as well as decrease the chances of health risks, work with a health care provider who understands GLP-1 medications and can also support you in lifestyle changes.

Vukasinov says obesity medicine providers monitor GLP-1 medication safety and success by:

• Tracking your weight, as well as your body composition (the percentage of muscle, bone and fat you have) and waist circumference.
• Monitoring lab values such as A1c, lipids and kidney and liver function
• Checking your vitamin levels, especially vitamin B12, vitamin D and iron, through blood work for deficiencies
• Asking you about symptoms such as GI side effects, mood and energy levels, and if you feel full after eating
• Reviewing your diet and protein intake
• Supporting you with doing resistance training to maintain muscle mass
• Adjusting your dosage, as well as adjusting or stopping other medications you might be on, such as medications for blood pressure and diabetes, as your other health conditions improve

You and your health care provider will also weigh the risks and benefits of continuing with GLP-1 medications or starting to wean off them. These are ongoing conversations you’ll have as your health care provider monitors you for adverse reactions and how well the medication is working.