It may take a few hours or days to reach Mounjaro’s peak time in your body. However, using Mounjaro over a longer period can lead to significant weight loss.

Mounjaro is a brand-name medication that’s approved by the Food and Drug Administration (FDA) to help manage blood sugar levels in people with type 2 diabetes. It is used alongside lifestyle changes and physical activities.

Mounjaro is not yet approved by the FDA for weight loss or weight management. However, Mounjaro may be prescribed off-label for this use. (Off-label use is where doctors prescribe you medication for different purposes than its approved uses.)

Mounjaro starts to work soon after you use it. However, it takes some time to reach peak levels in your blood. It may also then take some time to leave your system.

This article discusses how long it takes for Mounjaro to start working and the Mounjaro dosage for weight loss.

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Mounjaro starts to work within hours of your first injection. It then takes about 8 to 72 hours for the drug to reach peak levels in your system.

The active ingredient in Mounjaro is tirzepatide. Zepbound also contains tirzepatide and is FDA-approved for weight loss and weight management.

Tirzepatide works by imitating the effects of hormones called incretins. It mimics incretins known as GIP and GLP-1 by activating certain receptors (binding sites) in the body. This can help lower blood sugar levels and may reduce appetite, which can lead to weight loss.

Tirzepatide has a half-life of 5 days. (A drug’s half-life is the amount of time it takes for your body to get rid of half a dose.) So if you stop using Mounjaro, it takes about 30 days for the drug to get out of your system.

Using Mounjaro does not guarantee a specific amount of weight loss each week. However, experts recommend aiming for 1 to 2 pounds (lb) per week as a safe rate of weight loss.

Study results

In a 2022 study, researchers found that people using tirzepatide started experiencing weight loss within weeks. The amount of weight loss may depend on your dose of the medication and how well your body can manage higher doses.

The study looked at people with a body mass index (BMI) greater than 30 or people with a BMI greater than 27 with one weight-related complication, excluding diabetes. Tirzepatide was given along with recommended diet and exercise.

In the study, people were started on a tirzepatide dosage of 2.5 milligrams (mg) injected once per week. Then, the dosages were increased to either 5 mg, 10 mg, or 15 mg once per week for the rest of the study, which lasted 72 weeks.

Over the 72 weeks, people using 10 mg of tirzepatide lost on average 19.5% of their weight, while those using 15 mg lost on average 20.9% of their weight. The average weight loss for these doses was 48.9 to 52 lb. The people lost most of their weight loss during the first half of the trial.

The recommended dosage provided in the Mounjaro prescribing information is for its approved use, which is to help manage blood sugar levels in people with type 2 diabetes. The starting dosage for this use is usually 2.5 mg injected once every 4 weeks. If needed, the dosage may be increased.

The dosage of Mounjaro for helping manage blood sugar levels in people with type 2 diabetes may be helpful for weight loss as well. However, since Mounjaro is not FDA-approved for weight loss, the manufacturer does not provide recommended dosages at this time.

Zepbound, which contains the same active ingredient as Mounjaro but is FDA-approved for weight loss, also has a starting dosage of 2.5 mg once per week for 4 weeks. Doctors may then increase the dosage to 5 mg once per week. They may also continue to increase the dosage by 2.5 mg every 4 weeks if needed, up to a maximum of 15 mg once per week.

If your doctor decides to prescribe Mounjaro for weight loss, they will recommend the best dosage for you. Be sure to use Mounjaro as prescribed by your doctor.

Mounjaro is a prescription injection medication that is FDA-approved to manage blood sugar levels in people with type 2 diabetes. Doctors may also prescribe Mounjaro off-label for weight loss.

Mounjaro starts working within hours to a few days after injecting it. You may lose weight loss within a few weeks of starting Mounjaro treatment.

Doctors will determine the best dosage of Mounjaro for you. Your dose may vary depending on how well your body responds to the drug.

If you have questions about Mounjaro peak effect time and weight loss, talk with your doctor or pharmacist.