What to know about prescription drugs promising weight loss

WeightWatchers will be introducing its roughly 3.5 million subscribers to a new generation of medications that go beyond behavioral changes like gym workouts and diet tracking. Obesity experts say the drugs may revolutionize treatment of the disease that affects 42% of American adults.

Here's a look at the promise of these new medications and cautions about their use.

WHAT ARE THESE NEW DIET DRUGS?

The drugs that have generated most buzz are from a class of medications called GLP-1 agonists. Two of the most popular, Ozempic and Wegovy, are different doses of the same drug, semaglutide.

Ozempic has been used for six years to treat type 2 diabetes and is not approved for weight loss. Wegovy was approved in 2021 to treat obesity in adults and late last year to treat kids and teens 12 and older.

Doctors prescribe the medications to people with diabetes alone, or to people who are obese or who are overweight with additional health problems. Most of these types of drugs are delivered through weekly injections.

Supply problems and soaring demand last year led to a shortage of the drugs, but Novo Nordisk, the manufacturer, said those have been replenished.

HOW DO THE DRUGS WORK?

They mimic the action of a gut hormone that kicks in after people eat, boosting the release of insulin, blocking sugar production in the liver and suppressing appetite.

A newer drug, called tirzepatide, mimics the action of two hormones for even greater effect. The Eli Lilly and Co. drug, sold under the brand name Mounjaro, is now approved to treat diabetes, but the FDA granted fast-track status to review it to treat obesity. A decision is expected this spring.

With lower appetite and a greater feeling of fullness, people using these drugs eat less and lose weight.

HOW EFFECTIVE ARE THE DRUGS?

In a clinical trial, adults who took Wegovy saw a mean weight loss of nearly 35 pounds, or about 15% of their initial body weight. Adolescents lost about 16% of their body weight.

A clinical trial of Mounjaro, which is still being studied, saw mean weight loss of 15% to 21% of body weight depending on the dose, compared with a weight loss of about 3% for people taking placebo, or dummy drug.

WHY NOT JUST DIET AND EXERCISE?

In a typical weight-loss program where participants rely only on diet and exercise, about a third of people enrolled will lose 5% or more of their body weight, noted Dr. Louis Aronne, director of the Comprehensive Weight Control Center at Weill Cornell Medicine.

Most people find it difficult to lose weight because of the body's biological reactions to eating less, he said. There are several hormones that respond to reduced calorie intake to increase hunger and maintain body mass.

"There is a real physical phenomenon," he said. "There is a resistance mechanism that is a coordinated effort by the body to prevent you from losing weight."

WHAT ARE THE SIDE EFFECTS OF THE DRUGS?

The most common side effects are short-lived gastrointestinal issues such as nausea, vomiting, diarrhea, stomach pain and constipation.

Other possible side effects include thyroid tumors, cancer, inflammation of the pancreas, kidney and gallbladder and eye problems. People with a family history of certain thyroid cancers or a rare, genetic endocrine disorder should avoid the drugs.

WHAT SHOULD CONSUMERS WATCH OUT FOR?

These new medications could be an effective part of a multifaceted approach to weight loss, said Dr. Amy Rothberg, an University of Michigan endocrinologist who directs a virtual weight management and diabetes program called Rewind.

But she worries that programs like WeightWatchers are primarily interested in boosting enrollment — and profits.

"My hope is that they do their due diligence and have real monitoring of the patients taking the drugs," she said.

It's important to make sure that patients are taking the drugs for the intended purpose, to make sure there's no reason they shouldn't take the drugs and that they're monitored for side effects, she said.

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