The short version
Zepbound is a shot. You take it once a week. A doctor has to prescribe it.
Its plain name is tirzepatide. The same drug is sold as Mounjaro for people with diabetes. Same drug, different box.
In the biggest test, people lost about 21 percent of their body weight in about 17 months. For someone who weighs 250 pounds, that is around 52 pounds.
Nine out of ten people in the test lost at least 5 percent of their weight.
How it works
When you eat, your gut sends out chemical messages. These messages tell your brain that you are full. They also slow down how fast food leaves your stomach.
Most weight loss drugs copy one of those messages. Zepbound copies two. That seems to be why it works better than the older ones.
Scientists are still working out why two is better than one. They have ideas. They do not have a full answer. Anyone who tells you they know for sure is guessing.
What the tests showed
The main test was called SURMOUNT-1. About 2,500 adults took part. Some got the drug. Some got a fake shot with nothing in it. Nobody knew which one they had.
- People on the highest amount lost about 21 percent of their weight.
- People on the fake shot lost about 3 percent.
- People who also had diabetes lost less. That is normal for all these drugs.
A later test asked a different question. What happens if you stop? People who switched to the fake shot started gaining the weight back. People who kept going kept losing.
In 2024, it was also approved for sleep apnea. That is a problem where you stop breathing for short moments while you sleep. Losing weight helped.
What can go wrong
The most common problems are stomach problems. They are worst at the start.
- Feeling sick to your stomach
- Throwing up
- Diarrhea, or the opposite
Most people feel better after a few weeks. Some do not, and they stop taking it. That is the number one reason people quit.
Rarer problems are more serious:
- Trouble with the pancreas, an organ that helps you digest food
- Gallbladder trouble, which can happen when you lose weight fast
- Losing muscle along with fat, about one quarter of the total
A warning you should know about
In lab tests, rats on this drug got a rare thyroid cancer. Nobody knows if that happens in people. It may never happen in people at all.
But because of it, anyone with that rare thyroid cancer in their family should not take this drug. Your doctor will ask about this.
What nobody knows yet
- How it works over many years. The longest tests ran a few years. People may take this for decades. That data does not exist yet.
- Whether you can ever stop. So far, stopping means gaining it back. No one has found a way around that.
- Whether losing muscle matters later. This is a real worry for older people. Studies are running now.
The facts, in a box
- Plain name
- Tirzepatide
- Brand names
- Zepbound for weight. Mounjaro for diabetes.
- How you take it
- A shot under the skin, once a week
- Who makes it
- Eli Lilly
- Approved for
- Diabetes in 2022. Weight in 2023. Sleep apnea in 2024.
- Weight lost
- About 21 percent over about 17 months, at the highest amount
Where this came from
- Jastreboff and others, New England Journal of Medicine, 2022. The main SURMOUNT-1 test.
- Garvey and others, The Lancet, 2023. The test in people with diabetes.
- Aronne and others, JAMA, 2024. The test on what happens when you stop.
- Malhotra and others, New England Journal of Medicine, 2024. The sleep apnea test.
- The official Zepbound drug label from the FDA, including the thyroid warning.
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