Whether you like them or not, weight-loss drugs have changed the world. Obesity levels in the US, which had been on the rise for years, are falling.
National spend on food has shrunk, fashion outlets are selling fewer XXL-sized clothes and, here in the UK, one supermarket has even launched a ‘nutrient dense’ food range, aimed at helping people on these drugs adapt to their reduced food consumption – smaller portions, with more macronutrients.
Ozempic has fast become the poster child of these drugs, despite not being officially approved as a weight-loss drug in either the US or UK (it was designed to help those with type-2 diabetes).
It falls into a class of drugs alongside Wegovy and Mounjaro (which are approved for weight-loss) that mimic the hormone GLP-1, which your body uses to tell your brain that you’ve eaten enough.
The key ingredient in these appetite suppressants is usually semaglutide, or tirzepatide in the case of Mounjaro, but each one acts in a similar way.
Hijacking this mechanism can help those with obesity lose weight. This is important because carrying extra fat is a health risk – it makes you more likely to develop several conditions, from diabetes to heart disease, and even cancer.
But like any world-changing technology, semaglutide drugs have their critics.
In this case, it’s health influencers leading the charge. They would rather you fast, switch diets, take up exercise or, better still, spend a nominal amount to join their online programmes and courses.
That said, with the widespread public adoption of these drugs in recent years, reports of side effects have begun cropping up. In some cases, semaglutide has led to malnutrition, gastric issues, mental health issues and eye problems.
On top of that, many people are beginning to question what happens after they’ve lost the weight – how can they stop taking semaglutides and keep the inches off their waistlines?
As we learn more about the drug in the long term, are we beginning to discover that these weight-loss drugs have a dark side?
Body and brain
To start with, the way in which semaglutide drugs like Ozempic and Wegovy cause weight loss can be problematic. A weekly dose of semaglutide not only suppresses your appetite, but also delays the rate at which food leaves your stomach, helping you to feel full for longer.
But having food stay in your stomach for a long time can be uncomfortable and cause side-effects such as nausea, vomiting, constipation or, in extreme cases, severe bloating.
According to Dr Vanita Rahman, the clinic director at the Barnard Medical Center in Washington, DC, gastrointestinal problems are the most common side effect of semaglutide.
“It’s like when you have a stomach bug and feel like the food is just sitting there,” she says. “It just doesn’t feel good.”
Other worrying side effects being reported are mental health problems such as anxiety, depression and suicidal thoughts. Psychological changes like these might be possible because semaglutide affects the brain as well as the gut.
The drug modifies the activity of brain cells that produce dopamine and serotonin, chemicals that contribute to feelings of pleasure when you eat. This helps reduce cravings for high-fat or sugary foods, making them less enjoyable to eat.
But interfering with the release of these chemicals could have a knock-on effect on mood. At the same time, rapidly losing weight can also affect your body image and, hence, your mental health.
“A dramatic adjustment of body weight can trigger biological and psychological responses that can influence suicidal ideation,” says Amira Guirguis, a professor of pharmacy at Swansea University in the UK.
Guirguis and her colleagues conducted one of the first studies investigating whether there’s a link between drug-based weight-loss treatments and suicidal thoughts.
They analysed reports submitted to the US Food and Drug Administration (FDA) related to reports of suicidal thoughts or self-injury while taking semaglutide or drugs with a similar active ingredient and found that there was a relationship between the two.
They didn’t find a causal link, however, and reports could be related to other factors such as taking a high dose or existing mental health issues, says Garguis. Results from other studies haven’t found a link between semaglutide and suicidal thoughts.
“There isn’t sufficient data or strong evidence,” says Guirguis. “Also, it’s very important to consider that these drugs have only been used for weight-loss management for a few years, so we don’t have enough information to look at people who have been using them long term.”
Guirguis and her colleagues have since investigated another potential side-effect being reported: eye disorders.
In work published in December 2025, they analysed whether there’s a link between semaglutide and over 260 eye disorders by looking at data from the FDA Adverse Event Reporting System.
“These included things that were very scary, ranging from eye swelling to blindness,” says Guirguis.
The team found a strong association between usage of semaglutide and a rare disorder of the optic nerve, called non-arteritic anterior ischemic optic neuropathy (NAION), which can cause sudden vision loss, usually in one eye.
Having diabetes is a risk factor for the condition: when blood glucose levels drop quickly, less blood reaches the front of the eye’s optic nerve head and can trigger the condition.
Semaglutide seems like it could have a similar effect in some people, especially if someone has a pre-existing eye disorder.
“Compared to our first study (on suicidal thoughts), there’s much stronger evidence,” says Guirguis. “However, to confirm these findings, we need studies in the lab because, at the moment, it’s (based on) reporting [from patients].”
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Other concerns
Apart from side effects, the use of semaglutide for weight loss raises other concerns. A clinical trial found that an average user lost about 18kg (almost 40lbs) after taking the drug for 68 weeks.
Although this is positive, another clinical trial found that weight loss plateaus at around 65 weeks.
Furthermore, people typically don’t lose enough weight to reach a healthy body mass index (BMI) and remain in the ‘obese’ or ‘overweight’ categories. Only 12 per cent of users had a ‘normal’ BMI after using semaglutide for four years.
Experts also recommend that people continue to take semaglutide indefinitely to maintain their new weight. This is problematic since it has a high discontinuation rate, often because of side effects or the high cost of the drug.
When taken for weight loss, research has found that nearly 65 per cent of users of semaglutide (and similar GLP-1 receptor analogues liraglutide and tirzepatide) stop taking it within a year.
Furthermore, when people cease to take semaglutide, research has shown that they often quickly regain a lot of the weight they’ve lost: for example, more than 65 per cent of it one year after stopping.
The main issue, according to Rahman, is that semaglutide doesn’t address the underlying reasons that are driving people to consume more calories than they need.
For example, some people reach for ‘comfort food’, which is typically high in fat and sugar, as a way to cope with a stressful situation, or may overeat out of distraction when they’re in a hurry or doing something else.
Rahman, therefore, thinks that more needs to be done to educate the public about the causes of obesity.
“Nutrition plays a key role in its causation and a key role in its treatment,” she says. “Unfortunately, that’s starting to go by the wayside as people turn to medication.”
Proceed with caution
When taking any drug, you need to consider whether the benefits outweigh the risks. Guirguis thinks that semaglutide’s adverse effects are comparable to what you would expect from any drug.
For most people, its side effects are expected to be mild and manageable, while the more serious ones, such as eye disorders, are rare.
However, Guirguis’s concern is that many people are now trying to obtain these drugs from unregulated websites.
“People need to understand that this carries significant risks because these products may be fake, they may be expired or they may contain unsafe or unknown ingredients,” she says.
Whether this class of weight-loss drugs truly have a dark side will probably only become clear in the future when there’s more data about their prolonged use. In the meantime, the best advice is to proceed with caution.
“Semaglutide needs to be prescribed to the right patient at the right dose with proper follow-up and support,” says Guirguis.
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