People lost nearly 50 pounds on Zepbound — but gained more than half back when they stopped taking it

• Tirzepatide, a drug newly approved to treat obesity, helped people lose 20% of body weight on average.
• But growing evidence suggests patients need to keep taking the drug to maintain the results.

There's even more evidence that a wildly popular medication can help people lose significant weight and keep it off — but only if they continue taking the drug.

Tirzepatide, a once-weekly injection, is part of a group of medications that work by acting on a hormone called GLP-1 to help regulate appetite and blood sugar.

The drug has been available for diabetes treatment since 2022, sold under the brand name Mounjaro, . It was FDA-approved specifically for weight management in November of this year under the brand name Zepbound.

People taking tirzepatide lost an average of nearly 50 pounds in less than a year, but gained more than half of it back if they stopped taking the drug, according to a study published December 11 in JAMA.

A group of researchers from several universities, including Weill Cornell Medicine, looked at 670 people on tirzepatide as part of a clinical trial funded by the drug's manufacturer, pharmaceutical company Eli Lilly.

The participants took tirzepatide for 36 weeks, during which they lost an average of 20% of their body weight (roughly 46 pounds). Then, one group of patients was randomly assigned to a placebo instead of continuing the medication for the next 52 weeks. The patients in the other group were assigned to continue taking the drug during this time (although not all of the patients in either group completed the study, often for reasons unrelated to the medication).

The researchers found that people who stopped taking tirzepatide regained about 14% of their body weight — more than half of what they had initially lost — over the year of follow-up.

Meanwhile, the group who kept taking the drug not only maintained their results, but went on to lose even more weight (an additional 5.5% of their body weight, on average) over 52 weeks.

While the placebo group still ended up lighter than they had been at the start of the study, the results add to existing evidence that tirzepatide and similar drugs only work as long as patients keep taking them.

Semaglutide, sold as Ozempic and Wegovy, works the same way, as patients who stopped taking the drug regained about two-thirds of the weight they had lost, according to one study.

The findings also underscore what doctors have previously known about these medications: patients need to take them long-term, and possibly for life, to maintain the health benefits.

This phenomenon isn't unique to drugs used for weight management. Many common medications need to be taken continuously in order to help treat chronic conditions such as hypertension, diabetes, or high cholesterol.

However, doctors have previously said that patients can face major obstacles if staying on the medications over time.

Sides effects, shortages, and a high price tag can make weight loss drugs difficult to take long-term

Some research suggests that as many as two-thirds of people on weight loss drugs stop taking them within a year.

Factors like the cost of the drugs, ability to get them, and unwanted effects can all play role in people opting to discontinue them.

While tirzepatide is considered safe, it does have well-documented side effects, typically mild to moderate gastrointestinal issues.

In the most recent study, 80% of patients reported at least one side effect, usually nausea, diarrhea, constipation, or vomiting. And six people dropped out of the tirzepatide group in the follow-up year due to side effects.

Symptoms usually resolve over time, and gradually working up to the correct dose can help, too, doctors previously told Insider.

However, another concern for doctors is that patients sometimes struggle to afford the medications, which can cost $1,000 or more per month and may not be covered by insurance.

Finally, a high demand for the medications has also prompted shortages, leading to limited availability for patients who need them.

As a result, even people who have seen "life changing" results may struggle to stay on the medications if they can't afford them, or even fill their prescriptions.