Director Li Mei-Yueh, Division of Endocrinology and Metabolism, KMU Gangshan Hospital

Li Mei-Yueh, Director of the Division of Endocrinology and Metabolism at Kaohsiung Medical University (KMU) Gangshan Hospital, reminds the public that even after starting injectable therapy, diet and exercise habits must be adjusted in parallel to reduce the risk of rebound weight gain after discontinuation.

    The weight-loss injection tirzepatide (Mounjaro), often dubbed the “miracle weight-loss shot,” has recently gone viral among people seeking to lose weight and is seen as a quick shortcut to slimming down. However, physicians caution that clinical cases of “losing fast and regaining fast” are increasingly common. While the medication can produce substantial weight loss in a short period, the likelihood of regaining weight after stopping remains high if dietary and exercise habits are not changed at the same time.

    Li Mei-Yueh, Director of the Division of Endocrinology and Metabolism at KMU Gangshan Hospital, noted that the hospital treated a 36-year-old woman with a BMI of 31 (obesity). After evaluation, she received a weekly 5 mg injection along with dietary control and light exercise. Within three months, her weight dropped from 85 kg to 68 kg—a loss of 17 kg with clear results. However, when she returned four months after stopping the injections, her weight had increased to 79 kg. The main reasons were believed to be a return of appetite after discontinuation, combined with loss of muscle mass during weight loss and a reduced basal metabolic rate, making it difficult to maintain the result.

    Another case involved Mr. Chen, 42, with a history of diabetes. He used Mounjaro at 10 mg weekly for both glucose control and weight loss, reducing his weight from 92 kg to 70 kg after one year. But after the weight loss, his physical activity decreased and his eating habits did not change accordingly. Three months after stopping the medication, his weight rebounded to 80 kg.

    Li pointed out that studies show Mounjaro use can reduce body weight by an average of about 15% to 22%, but roughly one-quarter of that loss may come from muscle mass. Moreover, about 60% of patients regain weight within one year of stopping the drug. “If people return to their original lifestyle after losing weight, they are very likely to return to their original weight—and may regain even faster,” she warned.

    She explained that Mounjaro is a dual incretin medication (a GIP/GLP-1 receptor agonist). It was originally developed to treat type 2 diabetes and is indicated for patients with a BMI over 30, or a BMI over 27 with comorbidities such as diabetes, hypertension, or obstructive sleep apnea. It can delay gastric emptying, suppress appetite, and improve insulin resistance. However, it is not recommended for individuals with a history of medullary thyroid carcinoma, pancreatitis, severe renal impairment, or for pregnant and breastfeeding women.

    Recently, some people have reportedly purchased injections online and self-administered them. Li cautioned that the manufacturer recommends a 30-day shelf life after opening, and drug stability is critical because it affects both efficacy and safety. With online purchases, the source is unclear and authenticity, shipping conditions, and storage requirements are difficult to verify—posing very high risks. She advised seeking medical consultation. Physicians can gradually titrate the dose based on individual conditions to reduce side effects such as nausea, vomiting, constipation, hypoglycemia, and gallbladder disease, and to avoid serious consequences such as dehydration and malnutrition.

               Studies show that Mounjaro use reduces body weight by an average of about 15% to 22%, but carries risks such as muscle loss and weight regain within one year
               after discontinuation.

      “Mounjaro is a medical tool, not an all-purpose miracle slimming injection,” Li emphasized. During treatment and after discontinuation, patients should perform regular resistance training and consume sufficient daily protein to minimize muscle loss. At the same time, they should build stable eating and sleep routines and, under a physician’s assessment, taper and discontinue the medication step by step. Only by combining multiple approaches can weight-loss results truly be maintained.