Ozempic, Wegovy, Mounjaro: How these medications promote weight loss – and what you need to know

It's a new day for weight loss treatment, with anti-obesity medications coming on the market that appear safe, at least in the short-term. 

Two medications in this class, Ozempic and Mounjaro, are prescribed to treat diabetes. Wegovy, a higher dose of the same drug as Ozempic, is approved for weight loss.

Weight loss drugs have gotten a bad name over the decades, causing heart problems or other organ damage and helping people lose only a small fraction of excess weight.

Now, though, these new anti-obesity medications promise to shave off 15% to 20% of body weight.

That's not enough to make someone with obesity thin, but it will make a significant difference and should be enough to prevent or substantially improve health problems like diabetes and heart issues.

Related: Experts worry the 'magic' in new weight loss drugs carries a dark side

Here's what's currently known about these medications:

Wegovy vs. Ozempic

Semaglutide is the generic name for both Wegovy and Ozempic, which are made by Novo Nordisk. Wegovy is approved for weight loss, while Ozempic is used to treat people with diabetes.

Both drugs are given by weekly self-injections, though future generations might be available as pills.

Latest: Jimmy Kimmel joked about Ozempic at the Oscars. We need to actually talk about it.

Semaglutide: How Wegovy and Ozempic help you lose weight

The new medications are part of a class of drugs know as GLP-1 (for glucagon-like peptide 1) agonists. Essentially, they amplify a natural "fullness" signal between the stomach and the brain, encouraging people to stop eating sooner than they might otherwise.

In addition to Semaglutide, another newish treatment in this GLP-1 class of drugs is called Tirzepatide, sold as Mounjaro to treat diabetes and will likely be approved for weight loss later this year. Tirzepatide, made by Eli Lilly, includes a second medication that increases the stop-eating signal even more.

Semaglutide has been shown to help people drop about 15% of their weight on average, and tirzepatide closer to 20%.

For most people who have obesity, that level of weight loss will not make them "thin" – a 300-pound person who loses 20% of their body weight will still weigh 240 pounds – but is enough, experts say, to substantially reduce the health risks that come with excess pounds.

Side effects of weight loss drugs semaglutide and tirzepatide

Both drugs can cause nausea, vomiting, diarrhea, reflux and other side effects.

They are meant to be ramped up slowly, increasing the dosage over the first few months, to reduce these side effects. Some people take anti-nausea medication around the time of their weekly shot to control the sensation.

In a way, the nausea is a "feature not a bug," experts say. The drugs work by sending a signal to stop eating, which can be interpreted as gastrointestinal discomfort.

About 4% of people in a clinical trial stopped taking Wegovy because of side effects.

Results: Does Wegovy and Ozempic help keep weight off long term?

Doctors worry that patients don't understand the full implications of the medications.

Studies have so far followed people for only about two years, so it's not clear whether the medications can keep weight off longer or if there will be unanticipated effects later.

There's concern, particularly for children, whose parents are being encouraged to put them on the medications as young as age 12 to combat substantial excess weight. Some say the health risks of obesity outweigh any risks from the medications, but there have been no long-term studies of young people taking anti-obesity drugs.

Meanwhile, not everyone will benefit from the drugs, which have been shown useful for about 80% of people with obesity.

People also may not realize that they have to keep taking these drugs forever to keep the weight off and maintain any health improvements.

Doctors say people still need to exercise and eat a healthy diet to see the best results both in their waistline and their health.

How much do Wegovy, Ozempic and Mounjaro cost?

Wegovy retails for about $1,300 a month. Eli Lilly has not set a price for Mounjaro, once it is approved for weight loss, but it currently sells for about $1,000 a month.

Both Mounjaro and Ozempic are typically covered by insurance for people who have diabetes.

Another anti-obesity medication, called Contrave, has also helped some people lose weight, though studies show it leads to less weight loss than semaglutide and tirzepataide. Currax, the company that makes Contrave, has offered it for $99 per month for people who cannot get it covered by insurance.

READ MORE: Price of anti-obesity medications may be too expensive for most Americans

Does insurance or Medicare cover Wegovy or other weight loss drugs?

Most insurance plans, including Medicare, do not cover the cost of weight loss treatments other than some sessions with a nutritionist.

Historically, weight loss treatments weren't covered, in part because health experts thought people could control their weight through diet and exercise. Research has now shown lifestyle change to be ineffective for helping most people lose substantial weight. Human biology, evolved to combat starvation, fights to regain lost pounds.

Insurance coverage may change because of the new medications, which seem safe and effective, and under pressure from drug makers and the public. But the cost of these drugs make it hard for people – or insurers – to afford them.

Some doctors have prescribed diabetes drugs Mounjaro and Ozempic off-label for patients with pre-diabetes or even those without the disease, but many insurance companies will refuse to pay under those circumstances.

Eager for the drugs, some people have turned to other countries for less expensive prescriptions, but this is technically illegal and doctors worry about the risk of counterfeits. Weight loss drugs need to be taken indefinitely – or the weight and any related health problems will creep back – so it will be costly and difficult to keep up a supply obtained this way.

Demand spikes for Wegovy, Ozempic and Mounjaro

All three drugs have seen a significant increase in demand, with supply issues for Wegovy and Ozempic mostly resolved early this year.

According to SingleCare, a prescription savings service, demand for Ozempic rose 10% from November to December, 29% in January and 12% in February.

For Wegovy, prescriptions climbed 21% in December, 284% in January and 27% in February.

Mounjaro saw smaller increases in demand, with prescriptions rising 15% in December, jumping 59% in January and declining 6% in February.

Celebrity weight loss and gossip about Ozempic

Weight loss medications have been the talk of Hollywood, even earning a mention at the recent Academy Awards.

Comedian and actress Sheryl Underwood credits her 95-pound weight loss to dramatic lifestyle changes and Wegovy. Elon Musk famously took the medication. Other celebrities without obvious obesity, have also reportedly been taking Wegovy or Ozempic, though some, including the Kardashians, have begun denying it.

"Ozempic face," caused by rapid weight loss, is the latest concern raised by the medications.

And doctors say people shouldn't take these anti-obesity medications just to drop a few pounds. They are intended for people who need substantial weight loss for medical reasons, not people who want to loosen their size 2 skinny jeans.

More about America's obesity epidemic

More than 4 in 10 Americans fit the medical definition for having obesity, putting them at risk for serious health problems, including diabetes, heart disease and some types of cancer. Take a deeper look at this epidemic:

The science behind obesity: Why it's no longer considered a personal failing

Weight and stigma: Fat shaming won't fix America's obesity problem

What's the best diet for weight loss? What researchers have to say

The weight of inequality: What's to blame? Start with the system. 

What to know about new drugs and surgery: They come with a catch. 

Solutions:  The obesity epidemic can end with kids.

Contact Karen Weintraub at kweintraub@usatoday.com.

Health and patient safety coverage at USA TODAY is made possible in part by a grant from the Masimo Foundation for Ethics, Innovation and Competition in Healthcare. The Masimo Foundation does not provide editorial input.

This article originally appeared on USA TODAY: Ozempic for weight loss, explained: Side effects, costs, other drugs