By Dr. Asnat Raziel, bariatric surgeon specializing in obesity treatment, metabolic health and healthy longevity; Director of the Multidisciplinary Center for Obesity Treatment, Assia Medical, Assuta Ramat HaChayal, Tel Aviv
Is obesity medication safe? The short answer
Is obesity medication safe? It is one of the first questions my patients ask me. The short answer: for most people, under medical supervision, yes. The new medications have been tested in large trials, and their common side effects are well known and usually pass. However, there are also rare risks, and situations in which a medication isn’t suitable. In this article, I explain what we know today and how to reduce the risk.
Why people ask whether obesity medication is safe
The field has a complicated history. According to the Wikipedia overview of anti-obesity medication, the fen-phen combination was withdrawn from the market in 1997 because it damaged heart valves. Later, regulators also withdrew sibutramine, because of cardiac risk, and rimonabant, because of psychiatric effects. So the caution is understandable.
Today’s medications, however, are very different. They are based on natural gut hormones, they have been tested in thousands of participants, and they are under close safety monitoring. In addition, some of them have shown benefits that go beyond weight loss.
Which medications are available today
According to the US National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), the FDA has approved several medications for long-term use. They include orlistat, Contrave (naltrexone/bupropion), liraglutide (Saxenda), semaglutide (Wegovy) and tirzepatide (Zepbound, sold in Israel as Mounjaro). Most patients today receive medications from the GLP-1 family. You will find a broad overview of the options on my page about medications for obesity and metabolic disease.
Is obesity medication safe? Common side effects
The most common side effects of GLP-1 medications affect the digestive system. These are mainly nausea, diarrhea, constipation, vomiting and a feeling of fullness. In the STEP 1 trial of semaglutide, nausea and diarrhea were usually mild to moderate and eased over time. Only 4.5% of participants stopped treatment because of digestive side effects, compared with 0.8% in the placebo group.
Reducing these side effects is relatively simple. Increase the dose gradually, eat small portions and avoid very fatty food. It is also important to drink enough. If the symptoms don’t ease, your doctor can pause the dose increase or lower the dose. For a fuller picture, see my article on GLP-1 side effects.
Is obesity medication safe? Rare risks
Pancreatitis and the gallbladder
Studies have linked GLP-1 medications, at a low rate, to pancreatitis and gallstones. Rapid weight loss on its own also raises the risk of gallstones. So severe, persistent upper abdominal pain calls for seeing a doctor right away. Patients with a history of pancreatitis need an individual assessment. I discuss both issues in my articles on weight-loss drugs and pancreatitis and on gallstones and GLP-1 medications.
The thyroid
In rodents, GLP-1 medications caused thyroid tumors. In humans, no such link has been proven. Even so, according to NIDDK, people who have, or whose family members have, medullary thyroid cancer or MEN2 syndrome must not take Saxenda, Wegovy or Zepbound.
The eyes
In 2025, the European Medicines Agency concluded that NAION, a blood-vessel injury to the optic nerve, is a very rare side effect of semaglutide. It affects up to 1 in 10,000 patients. Any sudden loss of vision requires seeing a doctor immediately.
Mood and mental health
For a time, the labels of weight-loss medications carried a warning about suicidal thoughts. In January 2026, the FDA requested removal of this warning from Saxenda, Wegovy and Zepbound. After a comprehensive review, the agency found no increased risk. Nevertheless, any change in mood is worth discussing with your doctor.
Muscle mass
Part of the weight lost during treatment is lean body mass, including muscle. That is why it is important to eat enough protein and add strength training, as I explain in my article on preserving muscle mass during weight loss.
Is obesity medication safe for everyone?
No. According to NIDDK, you should not take weight-loss medications during pregnancy, when planning a pregnancy or while breastfeeding. Each medication also has its own restrictions. For example, Contrave isn’t suitable for people with seizures or uncontrolled blood pressure. In addition, these medications may interact with other drugs, herbal supplements and over-the-counter products. So tell your doctor about everything you take.
On the other hand, never buy injections from unregulated sources. A counterfeit product or a wrong dose poses a real risk, unlike the original medication.
Is obesity medication safe for the heart?
Here the news is especially good. The SELECT trial enrolled 17,604 people with heart disease and obesity, without diabetes. Semaglutide lowered the rate of major cardiac events to 6.5%, compared with 8.0% in the placebo group. In other words, it cut the relative risk by 20%. However, 16.6% of patients on semaglutide stopped treatment because of side effects, compared with 8.2% in the placebo group. A heart-healthy lifestyle adds to the benefit. You can read more about how semaglutide protects the heart.
How to keep treatment safe
- A full medical checkup before you start, including your medical history and medications.
- Gradual dose increases, according to the guidelines.
- Regular follow-up with a doctor, including blood tests as needed.
- A protein-rich diet, enough fluids and physical activity.
- Prompt medical attention for severe abdominal pain, a change in vision or a change in mood.
Medication is also just one part of a broader plan. A holistic approach also emphasizes sleep, stress management and emotional support.
Bottom line
Is obesity medication safe? For most patients, when it is given with medical follow-up, the answer is yes. The common side effects affect the digestive system and usually pass. Serious risks are rare, and most of them can be detected early. Moreover, in people with heart disease, semaglutide even reduced cardiac events. The key is personalized treatment and close follow-up.
This article provides general information and is not a substitute for personal medical advice.
Questions and answers
What are the most common side effects?
Nausea, diarrhea, constipation and vomiting. They are usually mild to moderate, appear at the start of treatment or after a dose increase, and fade over time.
Is obesity medication safe in the long term?
Yes. Obesity is a chronic disease, and researchers have tested these medications for long-term treatment. In the SELECT trial, for example, the average follow-up was 39.8 months.
Who should not take these medications?
Women who are pregnant, planning a pregnancy or breastfeeding. In addition, people who have, or whose family members have, medullary thyroid cancer or MEN2 should not receive GLP-1 medications. Each medication also has further restrictions.
What should I do if a side effect appears?
Contact your doctor. Sometimes simply pausing the dose increase is enough. Severe abdominal pain, loss of vision or distressing thoughts require immediate medical attention. You can also book an appointment with Dr. Asnat Raziel.
Sources
Prescription Medications to Treat Overweight & Obesity – NIDDK
Once-Weekly Semaglutide in Adults with Overweight or Obesity
Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes
Beyond diet and exercise: understanding holistic weight management
