FDA approves new weight loss drug with remarkable track record

November 13, 2023
Long white tube that says Zepbound tirzepatide injection, 2.5 mg.
Zepbound contains tirzepatide, which makes people feel full on less food and slows digestion. But there are side effects. Image by Eli Lilly and Company

Patrick O’Neil, Ph.D., director of the Weight Management Center at MUSC Health and a professor of psychiatry and behavioral sciences at the Medical University of South Carolina, is impressed by how effective the newest weight loss drug to win approval from the Food and Drug Administration appears to be. It’s called Zepbound.

“It was studied at three different doses. At the highest dose, the average weight loss was 20.9% of their starting weight,” O’Neil said.

“If you look at the trajectory of that and the other recently approved obesity medications, the amount of weight loss they’re producing is increasing. And with this product, it's nudging up into the area where it’s the kind of weight loss you'd expect with some types of bariatric surgery.”


Zepbound is doing that with the help of a key ingredient. “Terzepatide is a single compound, but it has actions on two types of receptors,” O’Neil said.

One, GLP-1, stands for glucagon-like peptide-1. It tells the brain when the body is full.

The second, a GIP receptor, stands for glucose dependent insulinotropic polypeptide. “That’s also stimulated when we eat. And it has effects in the brain as well as in fat tissue.”

The result is that the patient feels full on less food and the food moves more slowly through the digestive tract. 

Man smiling for portrait. He's wearing a pink shirt, a necktie and a suit jacket. 
Dr. Patrick O'Neil

O’Neil said it makes sense to go after more than one target when it comes to weight loss. “We've known for a long time that body weight is defended by multiple systems. So it's not like there's just one hormone or one neurotransmitter that's going to be completely responsible for weight gain or weight loss.”

Medical use

But O’Neil, who has worked in the field of weight management for decades, including a stint as president of the Obesity Society, wants people to keep in mind that Zepbound is for a medical condition. “This is not a medication to knock off 10 or 15 pounds. The FDA approval is for patients at a BMI of 30 or above, or in some cases between 27 and 30, if they have significant comorbid conditions," O'Neil said.

"The approvals for these medications are always when used in addition to diet and exercise, which sounds boring, but really is important. Learning proper nutrition, learning healthful eating patterns, learning how to construct a diet that's healthy, but at the same time, satisfying. And we know exercise is very important as well. And of course these are difficult behavior changes so learning behavior change techniques is also critical.  So they should not be considered a quick fix. They shouldn't be used just for small amounts of weight loss. And we need to recognize that since they will only work when you take them, these are likely long-term treatments.”

Side effects

People also need to recognize that the new weight loss drugs also come with well-documented side effects, O’Neil said. For example, in a news release about Zepbound, the drug’s manufacturer said it can cause gastrointestinal issues that can be severe in some cases.

The most common issues, seen in about 5% of clinical trial participants, included “nausea, diarrhea, vomiting, constipation, dyspepsia [indigestion], injection-site reactions,” according to the release. It includes further warnings as well.

To reduce the risk of severe problems, O’Neil said the drug is given in gradually increasing doses through a weekly shot. That slow ramp-up is important. 

“At the discretion of the physician and obviously the patient, if somebody's having some adverse reactions, problems with nausea or diarrhea, for example, then they would probably slow that escalation schedule or maybe just stay where they are or even back down the following week. The schedule can be adapted to the patient's tolerance of the medication,” O’Neil said.

Timing and cost

So when will the new drug hit the market? By the end of the year. As for the cost, the drug’s manufacturer said the list price will be around $1,060. But people who have insurance coverage for it may pay as little as $25 for a one or three-month prescription. And people who do have insurance but don’t have coverage that includes Zepbound may be able to pay about $550 a month, according to the news release.

The medication arrives during a period of tremendous growth in the weight loss drug marketplace. O’Neil said obesity is finally getting the attention it deserves. “The reason you want to treat it is because it can lead to so many other medical problems. This is not a cosmetic matter. It's not a vanity matter. Obesity is a serious health condition. We need to treat obesity seriously.”

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