Around one in 10 people experience side effects from weight loss medications14:40, 31 May 2026Brits who use weight loss jabs have been urged to “call 111” if they experience a potentially dangerous symptom. This could indicate a serious side effect affecting around one in 100 patients.‌Weight loss medications, also referred to as GLP-1 inhibitors, work by mimicking GLP-1 (glucagon-like peptide-1), a hormone naturally produced in the gut that plays a vital role in regulating blood sugar levels and suppressing appetite.‌GLP-1 inhibitors have seen a recent surge in popularity, largely due to their proven efficacy in managing blood sugar in people with diabetes and aiding weight loss. Delivered via injection, certain versions of these medications can be prescribed through the NHS to eligible patients.‌However, like any prescribed medication, it's essential to be aware of the potential side effects associated with these injections. On its website, the British Heart Foundation (BHF), explained that acute pancreatitis is one serious potential risk.Acute pancreatitis is a serious condition where your pancreas suddenly becomes swollen and painful (inflamed). Patient data suggests that as many as one in 100 people using these injections could encounter this condition.‌"Speak to a GP or call 111 if you notice any symptoms, such as a sudden severe pain in the middle of your abdomen," advised the BHF.According to the NHS, the main symptom of acute pancreatitis is pain in your tummy. You may also have a high temperature and feel sick or be sick (nausea and vomiting).The tummy pain may:‌Start suddenly and not go awayBe severe, sharp or knife-likeAffect the upper part of your tummy (between your ribs), one side of your tummy or your whole tummySpread to your sides and backFeel worse after you eat, move around or lie downFeel better when you lean forward or bring your knees to your chest (fetal position)Less serious side effectsThe BHF notes that "not everyone" will necessarily experience side effects from the treatment. However, it is "very common" for individuals to experience digestive problems, such as nausea, diarrhoea, constipation, and abdominal discomfort.The BHF explained: "These side effects affect one in 10 people, according to the patient leaflets that come with Mounjaro and Wegovy. The injections can also cause tiredness or dizziness, hair loss, low blood sugar and a fast heart rate in some people.‌"Speak to your doctor if you're experiencing any side effects, as you may need to take a lower dose or stop taking them."Vision problemsVision loss is another concern. The Medicines and Healthcare products Regulatory Agency (MHRA) has warned that "very rarely" individuals using semaglutide (the generic name for Wegovy) may experience a "sudden deterioration" in their eyesight, leading to total or partial vision loss, typically affecting one eye at a time.‌The BHF stated: "If you experience this issue you need to seek urgent medical care and be referred to a specialist eye doctor."Poor nutritionPoor nutrition is another potential downside due to the way these medications work, likely causing you to eat less. The BHF cautioned that this could result in nutritional deficiencies.The charity added: "And rapid weight loss may lead to reduced muscle and bone mass too. That's why eating a healthy balanced diet is still important.‌"Small, regular meals containing enough lean protein, calcium and vitamin D, and regular exercise can help to protect your muscle and bone health."Contraceptive pillThe MHRA has also cautioned that Mounjaro could diminish the effectiveness of the contraceptive pill. It continued: "It recommends using another non-oral form of contraception, like a condom, instead.Article continues below"And the MHRA also says you should not use weight-loss injections if you are pregnant, trying to conceive or breastfeeding."If you encounter any adverse side effects from your medication, it's advised to contact your GP immediately.