Endocrinologist explains dark side of weight loss drugs: Potential risks and benefits of Ozempic, Mounjaro, Wegovy

Dr Saptarshi Bhattacharya shared how weight loss injections can help you keep off the weight – but are they actually safe? Here's everything you need to know.

While Ozempic has dominated the weight loss space, Wegovy and Mounjaro are other injectable prescription weight loss drugs worth knowing about. But can these weight loss injections actually help people lose weight and keep it off? What about the health risks and side-effects? While these medications can serve a very important purpose for some people, they also come with certain risks

Endocrinologist explains the benefits, risks, and unanswered questions about weight loss injections. (Freepik)

In an interview with HT Lifestyle, endocrinologist, Dr Saptarshi Bhattacharya, senior consultant, Indraprastha Apollo Hospitals, Delhi and secretary, Endocrine Society of Delhi, said that for some people, these anti-obesity injections, hailed as groundbreaking solutions, seem like a beacon of hope.

“Yet even as their popularity surges, a shadow of controversy looms. In the US, the manufacturers are facing legal trouble, with lawsuits claiming that they downplayed the risks of serious side effects associated with these products. These challenges make us pause and question the safety of these seemingly miraculous injections,” he said.

According to Dr Bhattacharya, while the manufacturing companies maintain that they did nothing wrong, scrutiny is increasing, urging everyone to reexamine the safety of these treatments: “Against this backdrop, it becomes important to turn to medical evidence rather than headlines.”

Are anti-obesity injections really effective?

Dr Bhattacharya said, “The medical literature clearly demonstrates the efficacy of anti-obesity injections, such as semaglutide (Wegovy and Ozempic) and tirzepatide (Mounjaro), marking a new era in weight management. Clinical trials have demonstrated that these medications can lead to substantial and sustained weight loss.”

He elaborated: “For instance, studies on semaglutide have reported an average weight loss of 17 percent over 68 weeks, with one-third of participants shedding 20 percent of their body weight. To put this into perspective, a person weighing 100 kg could expect to lose 17 kg on average, and in one-third cases, more than 20 kg.”

He added, “Tirzepatide has shown comparable, and in some cases, even greater efficacy in terms of weight loss. On average, participants lost about 15-20 percent of their body weight, a scale of reduction once thought possible only after bariatric surgery. Remarkably, about half of those on the 10 mg dose and nearly 60 percent on the 15 mg dose lost more than 20 percent of their body weight. In contrast, just 3 percent of people on placebo, who were receiving dietary and exercise advice, achieved that milestone. These numbers explain the global buzz around these medicines.”

According to Dr Bhattacharya, these medications bring about cardiac and metabolic benefits beyond just shedding kilos. “They improve blood glucose, blood pressure, and lipid profiles and reduce systemic inflammation. Notably, semaglutide minimises the risk of major adverse cardiovascular events in individuals with heart disease. Research also points to improvements in conditions linked to obesity, such as obstructive sleep apnea and metabolic dysfunction-associated steatotic liver disease, commonly known as fatty liver, further reinforcing the wide-ranging health benefits of these drugs.”

Dr Saptarshi Bhattacharya said the medical evidence clearly demonstrates the benefits of these medicines, including significant weight loss, improved blood glucose control, reduced cardiovascular risk, better sleep apnea outcomes, and protection of liver and kidney health. (Shutterstock)

So where is the hesitation?

While anti-obesity jabs promise dramatic results, they don’t come without side-effects. Dr Bhattacharya shared that the most common problems involve the gut, such as nausea, diarrhea, constipation, abdominal pain, and sometimes vomiting. He said that nausea tops the list, affecting up to 44 percent of people taking semaglutide and approximately 30 percent of those taking tirzepatide.

“Diarrhoea is also frequent, seen in 20–30 per cent of users, while vomiting affects about 10–15 percent and constipation 10–20 percent. For most, these symptoms are mild to moderate in intensity, occur in the early weeks of therapy or after a dose change, and tend to ease off with time. Persistent or severe bouts of vomiting and diarrhea can cause dehydration, and about 5–7 percent of users discontinue the injections because of these problems. Doctors usually recommend starting with a low dose and then increasing it gradually, which helps the body adapt and keeps side effects in check,” Dr Bhattacharya added.

He said these gut problems are predictable and, in fact, arise from the same appetite-suppressing action that makes the drugs effective. But the real worry, according to Dr Bhattacharya, is this: could the risks go beyond just nausea and diarrhoea? “Reports have raised concerns about rare but serious complications such as pancreatitis, gut blockage called gastroparesis and paralytic ileus, and a vision problem known as non-arteritic anterior ischemic optic neuropathy (NAION), which can lead to sudden vision loss. Although these serious events are rare, their possibility means that the medicines still require careful monitoring, even as they help many people lose weight effectively,” he said.

Do these medications increase risk of pancreatitis?

Dr Bhattacharya said large-scale clinical trials offer reassurance, showing that the risk of pancreatitis (inflammation of the pancreas) with these medications is very low, often no higher than with a placebo (dummy medicine): “For example, a large trial of semaglutide reported acute pancreatitis in just 0.5 percent of users compared to 0.7 percent in those taking placebo. Similarly, tirzepatide trials demonstrated extremely low rates, with one study finding pancreatitis in 0.3 percent in both the medicine and placebo groups. While databases of reported side effects and individual case reports do show instances of pancreatitis and reinforce the need for continued vigilance, this doesn't prove that the medications directly cause the condition or significantly increase the overall risk for everyone.”

He added, “Individuals with type 2 diabetes and obesity already have a higher baseline risk for pancreatitis, and slightly elevated pancreatic enzymes (lipase and amylase) are common in these conditions without indicating actual disease. Nevertheless, users (of these drugs) should remain vigilant for symptoms of severe abdominal pain, especially if radiating to the back, and seek urgent medical attention if it occurs. Doctors use these injections with extreme caution, or even avoid them, in people with a prior history of pancreatitis or those at higher risk.”

What is paralytic or gastrointestinal ileus?

According to Dr Bhattacharya, a rarer concern is paralytic ileus, where the intestines stop moving properly. The US federal drug monitoring body, the FDA, has issued a warning regarding gastrointestinal ileus on the label for semaglutide, he said.

“This alert comes after post-marketing reports from users. While the exact cause is still under investigation, semaglutide and tirzepatide are known to slow gastric emptying and alter bowel motility. A detailed scrutiny, however, found that semaglutide itself was not significantly associated with an increased risk of bowel obstruction or ileus. For tirzepatide, while general digestive side effects are common, precise rates for paralytic ileus are less clear, though individual cases of partial small bowel obstruction have been noted. Severe or persistent abdominal pain, bloating, distension, or an inability to pass gas or stool may indicate ileus and require immediate medical attention,” Dr Bhattacharya shared.

Dr Saptarshi Bhattacharya said people on weight loss drugs should remain vigilant for symptoms of severe abdominal pain, especially if radiating to the back, and seek urgent medical attention if it occurs. (Freepik)

Concerns about NAION

A vision-related concern that has come into focus is non-arteritic anterior ischemic optic neuropathy (NAION). Dr Bhattacharya shared the European Medicines Agency (EMA) recently concluded that NAION is a very rare side-effect of semaglutide, estimated to affect up to 1 in 10,000 users.

“A large US study of more than 159,000 participants with type 2 diabetes found that during a two-year follow-up, NAION occurred in 0.04 percent of those taking semaglutide or tirzepatide compared with 0.02 percent in a matched comparison group. While the connection is not proven, and large studies have not shown a clear rise in eye complications, the signals warrant closer monitoring. NAION is already more common in people with diabetes, high blood pressure, and sleep apnea, but any sudden change in vision while on these medicines should not be ignored,” he said.

Where do we stand now?

“A 2024 poll found that approximately 6 percent of US adults, or nearly 6 million people, were taking a GLP-1 agonist, such as semaglutide, making these the most widely used anti-obesity medications in history. Millions more worldwide have benefitted, and demand continues to surge, straining global supply chains,” Dr Bhattacharya said.

Alongside this unprecedented uptake, legal concerns have emerged. Dr Bhattacharya shared: “As of September 2025, more than 2,600 lawsuits are pending in federal courts in Pennsylvania, USA, targeting both Novo Nordisk, the maker of Wegovy, and Eli Lilly, the maker of Mounjaro. Plaintiffs allege that the manufacturers failed to adequately warn patients and doctors about serious side effects, including gastroparesis and ileus, gallbladder disease, and NAION. A federal judge has ruled that for gastroparesis claims to proceed, the user must provide objective medical evidence such as gastric emptying studies, a move likely to narrow the number of viable claims.”

The legal developments underscore the importance of carefully selecting suitable candidates and maintaining ongoing monitoring. “The medical evidence clearly demonstrates the benefits of these medicines, including significant weight loss, improved blood glucose control, reduced cardiovascular risk, better sleep apnea outcomes, and protection of liver and kidney health. The presence of rare side effects should not dissuade individuals who stand to gain from these treatments. However, there must be clear communication regarding the risks and warning signs associated with their use,” Dr Bhattacharya said.

“Striking a balance between caution and proactivity is key, given the long-term and often-ignored consequences of untreated obesity. As with any medicine, informed discussion with the doctor remains key. For people like Meera, who have struggled with weight for years despite relentless efforts, informed discussion with a healthcare provider can help them safely access these treatments and achieve lasting benefits,” he concluded.

Note to readers: This article is for informational purposes only and not a substitute for professional medical advice. Always seek the advice of your doctor with any questions about a medical condition.