The U.S. Food and Drug Administration approved Eli Lilly's keenly-awaited obesity treatment on Wednesday, introducing a powerful rival to Novo Nordisk's popular weight-loss therapy Wegovy.

The once-weekly injection, which contains the same active ingredient as Lilly's big-selling type 2 diabetes treatment Mounjaro, will be sold under the brand name Zepbound. The following are key facts about the drug based on the FDA-approved label for its use and clinical trial data:

WHO CAN USE THE DRUG?

Like Wegovy, the FDA approved Zepbound for adults who are considered obese using a measure known as body mass index (BMI), a ratio of weight to height. People are eligible for the drug if they have a BMI of at least 30 or higher, as well as for patients with a BMI of 27 if they have at least one weight-related health condition like diabetes or high blood pressure.

The drug should be used along with a reduced calorie diet and increased physical activity. Zepbound should not be used with other drugs that belong to the same class of medicines known GLP-1 receptor agonists.

HOW DOES IT WORK

The GLP-1 class of drugs like Wegovy, Novo's related Ozempic and Zepbound were originally developed to help control blood sugar in patients with type 2 diabetes but also slow digestion and reduce hunger.

Ozempic and Wegovy share the same active ingredient, semaglutide, while Mounjaro and Zepbound are both tirzepatide.

SAFETY WARNINGS

The drug's label contains a warning that it has caused thyroid C-cell tumors in rats, similar to Wegovy.

The FDA says Zepbound should not be used in patients with a personal or family history of medullary thyroid cancer or in patients with a rare genetic condition called Multiple Endocrine Neoplasia syndrome type 2, which causes tumors in the endocrine system.

The drug also comes with warnings similar to those for Wegovy, which include the risk of severe gastrointestinal disease, kidney and pancreatitis-related issues, hypersensitivity reactions and suicidal behavior and ideation. It should also not be used during pregnancy due to a risk of fetal harm.

WHAT CAN IT DO?

In clinical trials, people taking Zepbound on average lost 48 pounds (21.8 kg) at the highest dose and 34 pounds (15.4 kg)on average at the lower dose. It also helped some patients lose over 25% of their body weight in its trials.

COMMON SAFETY ISSUES

Side effects can include nausea, diarrhea, vomiting, constipation, abdominal discomfort and pain. Other adverse effects listed in the drug's label include injection site reactions, fatigue, burping, hair loss and gastroesophageal reflux disease.