Approximately 2.4 million people in the United Kingdom are currently using weight-loss injections such as Wegovy and Mounjaro, which are designed to mimic the hormone glucagon-like peptide 1 (GLP-1) to help suppress appetite. These medications have been recognized for their potential to reduce body weight by up to 20%, while also contributing to the prevention of heart disease, certain cancers, and aiding in the treatment of addiction and depression. However, emerging research and patient reports have highlighted a range of side effects associated with their use.
A recent review of 21 studies involving advanced body composition scanning has revealed that nearly one-third (31.5%) of the weight lost from these injections consists of fat-free mass, including muscle and bone density. This proportion is considerably higher than the 14.3% seen in individuals who lose weight through diet and exercise alone. Experts warn that this loss of muscle and bone density may lead to long-term consequences such as increased risk of osteoporosis and frailty, particularly in older adults. To mitigate these effects, health professionals recommend incorporating resistance training two to three times per week, alongside aerobic exercise totaling 150 to 300 minutes weekly, during treatment with GLP-1 drugs.
Concerns about hair loss have also surfaced. A study analyzing health records of 50,000 users of GLP-1 weight-loss medications found that these patients were 68% more likely to experience alopecia, a rare form of hair loss, compared to those on other diabetes medications. While the overall risk appears low, this potential side effect is under review by the U.S. Food and Drug Administration. Researchers suggest that sudden calorie reduction and nutrient deficiencies may be contributing factors.
Weight regain remains a significant challenge following discontinuation of GLP-1 therapies. According to an analysis of 11 studies involving over 6,300 adults, patients typically lost an average of 8 kilograms during treatment but returned to their baseline weight within ten months after stopping the medication. This pattern has led scientists to propose that continued, possibly lifelong, use of the drugs may be necessary for sustained weight management. However, some patients discontinue use due to cost, side effects such as nausea and vomiting, or plateauing weight loss.
Other reported side effects include gastrointestinal issues like nausea, vomiting, diarrhea, constipation, stomach cramps, indigestion, and bloating. While often manageable, these symptoms can sometimes be severe enough to prompt cessation of treatment. Rare but serious adverse events, including gallbladder removal and acute pancreatitis, have also been documented.
Additional concerns involve dental health and nutrition. Because GLP-1 drugs slow gastric emptying, repeated vomiting can cause irreversible tooth enamel erosion. Experts advise patients who vomit to rinse their mouths with water or mouthwash and wait at least 30 minutes before brushing teeth to minimize acid damage. Furthermore, a consensus statement from a major European obesity conference emphasized the importance of maintaining a nutrient-dense diet rich in protein, fiber, and fluids during treatment, cautioning that simply eating less without improving food quality can lead to malnutrition.
Although GLP-1 weight-loss injections offer significant benefits, medical professionals stress the importance of careful management, including exercise, dietary quality, and monitoring for side effects, to ensure the safest and most effective outcomes.