People using injectable weight loss drugs may need long-term medical and lifestyle support, researchers have warned, after a large study found that weight is regained far more quickly than with traditional diet and exercise plans. Scientists at the University of Oxford found that people taking medications such as semaglutide (Wegovy) and tirzepatide (Mounjaro) lose weight while on treatment, but typically regain it within around 20 months after stopping the injections.The study also showed that improvements in blood sugar control, cholesterol levels, and blood pressure fade once the drugs are discontinued, leaving patients back at their original health markers. By comparison, people who lose weight through structured diet and exercise programmes tend to maintain the loss for longer, close to four years on average, although most eventually regain weight as well.Health Gains Reverse After Treatment EndsThe findings come alongside separate research from University College London and the University of Cambridge, which suggests that people prescribed newer weight loss drugs could face risks such as nutrient deficiencies and loss of muscle mass. Under current NHS rules, Wegovy can only be prescribed for up to two years, while Mounjaro has no set time limit.Most people using these medications pay for them privately, due to strict NHS eligibility criteria. Research indicates that around half stop treatment, often because of cost, side effects, or because they feel they have reached their target weight.The Oxford analysis, published in the British Medical Journal, reviewed 37 studies involving more than 9,000 participants. On average, people stayed on medication for 10 months and were followed up for eight months after treatment ended.Across all weight loss drugs, participants lost an average of 8.3 kg during treatment, but regained 4.8 kg within a year, returning to their starting weight within about 1.7 years. Those taking Wegovy or Mounjaro lost nearly 15 kg, but regained around 10 kg in the first year after stopping. Based on projections from one year of data, full weight regain occurred within roughly 1.5 years. Measures linked to heart and metabolic health, including blood glucose and cholesterol, also returned to baseline within about 1.4 years.Experts Say Obesity Requires Ongoing CareProfessor Susan Jebb, professor of diet and population health at the University of Oxford and an adviser to ministers and the NHS on obesity, said the findings were clear. “What we’ve shown is that weight regain after medication is common and happens quickly. The benefits for blood sugar and cholesterol closely track weight changes, so when weight comes back, those benefits disappear too.”She noted that weight regained after medication happens almost four times faster than after behaviour-based programmes, regardless of how much weight was initially lost. Professor Jebb said long-term solutions may be necessary, whether through ongoing medication, behavioural support, or a combination of both.“Obesity is a chronic, relapsing condition,” she said. “It’s reasonable to expect that treatment may need to continue for life, much like medicines for high blood pressure. We should think of this as long-term treatment for a long-term condition.”She added that combining diet and exercise programmes with drug treatment helps people lose more weight initially. However, once medication stops and appetite returns, those strategies alone often fail to prevent regain. In contrast, people in behavioural programmes without drugs may practice these habits more consistently, which could explain why weight regain is slower.Professor Jebb said it is clear that some form of ongoing intervention is needed if the benefits of weight loss drugs are to last. Some patients try tapering doses or using medication intermittently, while others rely on lifestyle support alone, but she said evidence on what works best remains limited.Sam West, a postdoctoral researcher at the University of Oxford and co-author of the study, said: “People on medication lose more weight than those in behavioural programmes, but they regain it about four times faster.”The researchers also questioned whether long-term drug treatment is cost-effective for the NHS. They concluded that since obesity is a long-term, relapsing condition, extended use of weight management medications may be needed to maintain health benefits.Concerns Over Nutrition and Muscle LossSeparate findings published in Obesity Reviews highlighted gaps in nutritional guidance for people taking semaglutide and tirzepatide. Dr Marie Spreckley from the University of Cambridge said many patients receive little structured advice on diet quality, protein intake, or micronutrient needs, despite significant appetite suppression.“If nutritional care isn’t built into treatment,” she said, “there’s a real risk of trading one health problem for another, through avoidable nutrient deficiencies and unnecessary muscle loss.”An NHS spokesperson said that while these drugs are a valuable addition to weight loss treatment, they are not a quick fix. “They must be combined with lifestyle and behavioural support, including advice on healthy eating and physical activity, to help people maintain weight loss over time,” the spokesperson said.