How do weight-loss drugs work and what are the most concerning side effects?
Weight-loss drugs can be life-changing for people who have struggled to lose weight, however, some people who take them experience unpleasant side effects.
In 2024, roughly 5 per cent of Britons had used an injectable glucagon-like peptide-1 (GLP-1) receptor agonists, a class of medications known under brand names such as Wegovy, Ozempic and Mounjaro, which works by mimicking the hormone GLP-1 to slow down digestion and lower appetite.
However, 1 in 10 patients using GLP-1 receptor agonists experiences gastrointestinal side effects, which are usually not serious but can lead to more serious complications.
How do GLP-1 receptor agonists work and what are the most concerning side effects?
How do GLP-1 receptor agonists support weight loss?
GLP-1 receptor agonists mimic the GLP-1 hormone by binding to GLP-1 receptors.
This triggers a number of effects such as slowing digestion, as the body releases less glucose from flood into the bloodstream. It also increases the feeling of fullness by affecting areas of the brain that process hunger.
What are the side effects?
The most common side effects of GLP-1 agonists drugs are nausea, vomiting, diarrhea and constipation. Other side effects include dizziness, headaches, increased heart rate and infections.
Harvard Medical School advises that small steps can be taken to manage some of these symptoms. For example, eating crackers, mint or ginger-based food and drinks about 30 minutes after taking GLP-1 agonists can help combat nausea.
Staying well-hydrated, avoiding dairy products and eating high-fiber foods can also help alleviate symptoms like nausea, diarrhea and constipation.
There are also a number of rare but serious side effects including pancreatitis, medullary thyroid cancer and acute kidney injury.
Dr Naveed Asif, GP at The London General Practice, advises that patients taking GLP-1 drugs should with a lower dose and gradually titrate up to help minimise the risk of these serious side effects.
“Careful, gradual reduction of insulin doses and close monitoring of blood glucose levels are also essential,” Dr Asif said, “Additionally, I want to stress the importance of obtaining Ozempic from reputable sources. There have been instances of falsified products in the UK that can pose serious health risks.”
Which side effects are most concerning?
According to Kiran Jones, a clinical pharmacist at Oxford Online Pharmacy, some of the most concerning side effects of GLP-1 drugs include gastrointestinal complications such as stomach paralysis, which can “significantly slow the movement of food through the stomach, causing long-term digestive issues that can cause severe medical complications”.
Jones added: “If used in combination with other diabetic medications, it can increase the risk of hypoglycaemia, and research indicates there is a link between the drug and pancreatitis. This is when the pancreas becomes inflamed and can quickly become serious enough to require hospitalisation.”
Another risk is cardiovascular complications, particularly for people with pre-existing heart conditions.
There have also been instances of dangerously low blood sugar (hypoglycaemia), especially when Ozempic is used in combination with other diabetic medications or when it is misused,” Jones said.
