Hong Jin-ho says he regained weight after stopping Mounjaro — here's why that happens

Obesity drugs Mounjaro (tirzepatide) and Wegovy (semaglutide) have drawn wide attention for their weight-loss effects, but a significant number of users experience rebound weight gain — commonly known as the "yo-yo effect" — after stopping the medication. Interest in the long-term effectiveness of these drugs has grown after broadcaster Hong Jin-ho revealed he regained weight following his Mounjaro injections.

In a preview for SBS variety show "Running Man" that aired Sunday, host Yoo Jae-seok remarked that Hong had looked noticeably slimmer on a previous appearance. Hong replied that he had lost weight while on Mounjaro but experienced severe rebound weight gain after stopping. He had also disclosed earlier this year that he was using an obesity drug.

Specialists say the phenomenon is far from uncommon. Rather than a cure for obesity, these drugs are better understood as tools for ongoing weight management.

Mounjaro and Wegovy suppress appetite and increase feelings of fullness while slowing gastric emptying, making it easier to feel satisfied with smaller amounts of food. Many users also report a reduction in food cravings and the urge to overeat.

Once the medication is stopped, however, these physiological effects gradually fade. Appetite naturally returns, food intake rises, and the likelihood of weight regain increases. Experts view this not as a failure of willpower but as a normal biological response to the drug wearing off.

Clinical trials have confirmed these findings.

In the STEP 1 extension study — a landmark trial for Wegovy — participants who lost an average of 17 percent of their body weight over roughly 68 weeks of treatment regained about two-thirds of that lost weight within a year of stopping the drug.

Similar results emerged from the SURMOUNT-4 study for Mounjaro. After all participants lost weight on the drug, one group continued treatment while another switched to a placebo. Those who kept taking the medication continued to lose weight, while those who stopped showed a clear tendency to regain it.

For this reason, experts say obesity should be treated as a chronic condition requiring long-term management — much like hypertension or diabetes. Decisions about continuing drug treatment are generally made in consultation with a physician, taking into account the individual's health status, target weight, side effects, cost and family planning.

That said, not everyone needs to stay on obesity medication indefinitely. Gastrointestinal side effects — including nausea, vomiting, diarrhea and abdominal pain — lead some patients to discontinue treatment or adjust their dosage. When necessary, treatment strategies can be modified by slowing the dose escalation schedule or switching to a different drug.

Stopping the medication does not automatically trigger rebound weight gain, but maintaining weight loss is difficult. When body weight drops, the body interprets this as an energy-deficient state and activates a "weight-defense mechanism" that raises appetite and reduces energy expenditure.

Some people also find that their appetite does not decrease as much as expected even while taking obesity drugs.

Experts attribute this to significant individual variation in response to GLP-1 and GIP receptors. The appetite-suppressing effect may also be insufficient during the initial low-dose phase, which is used to minimize side effects.

Lifestyle factors are another important variable in how well the treatment works. Stress, sleep deprivation, late-night eating and emotional eating are difficult to address through medication alone. Even with reduced hunger, habitually snacking or frequently consuming high-calorie foods can limit weight-loss results.

To maintain weight after stopping obesity medication, experts advise getting adequate protein, consistently combining strength training with aerobic exercise, sleeping enough, managing stress and regularly monitoring body weight. Catching small weight changes early, they emphasize, can help prevent the yo-yo effect before it takes hold.