How long does it take for Mounjaro to work?

In this article:

• How fast does it work?
• What affects results
• Can you regain weight?
• Mounjaro vs. Ozempic
• Bottom line

In this article

• How fast does it work?
• What affects results
• Can you regain weight?
• Mounjaro vs. Ozempic
• Bottom line

While the primary goal of diabetes medications is to regulate blood sugar levels, some have the added benefit of helping with weight loss. One such medication is Mounjaro (tirzepatide), a GIP/GLP-1 receptor agonist manufactured by Eli Lilly. It stimulates insulin production, decreases appetite, and slows digestion. In addition to improved glucose control, it commonly helps patients reduce their food intake. That’s why even though the medication is only approved by the Food and Drug Administration (FDA) for Type 2 diabetes, it’s also used off-label as a weight-loss drug. 

Mounjaro starts working quickly. You may notice decreases in appetite almost immediately and improvements in blood sugar and weight within a few days to several weeks, though the rate of weight loss varies by person. Keep reading to learn what to expect if you’re prescribed this medicine.

How fast does Mounjaro work?

You’ll notice decreased hunger and food cravings almost immediately after you take Mounjaro, says Alexander Nathanson, MD, an obesity medicine physician at NYC Health + Hospitals/South Brooklyn Health in New York. For example, you may notice that you’re unable to finish the same portion sizes you used to. However, it may take several days or weeks after starting Mounjaro to notice changes in your blood sugar control and weight. 

Blood sugar

Patients using Mounjaro for diabetes should notice some improvement in their blood sugar control within days of starting treatment. “Mounjaro allows the pancreas to produce insulin in a more efficient or ‘dose-dependent’ manner in response to food, a process that’s often impaired in those with Type 2 diabetes,“ Dr. Nathanson says. 

Sustained changes in blood glucose levels are likely within one to two weeks of starting Mounjaro, says Kevin Codorniz, MD, the division chief of endocrinology at Loma Linda University Health in California. However, some patients may have a delayed response or require a higher dose of Mounjaro to achieve significant effects.

According to the SURPASS-5 clinical trial, after 40 weeks on varying doses of tirzepatide, participants experienced an average reduction in A1C of 2% with the 5 mg dose, 2.4% with the 10 mg dose, and 2.34% with the 15 mg dose.

RELATED: How to save on Mounjaro

Weight loss

“After the first dose of tirzepatide, patients may already experience a decrease in appetite,” Dr. Codorniz says. And while every individual is different, many patients will start to see some weight loss within the first four weeks of starting tirzepatide, he says. 

Mounjaro mimics the actions of glucagon-like peptide-1 (GLP-1) and gastric inhibitory polypeptide (GIP; also called glucose-dependent insulinotropic polypeptide), two naturally occurring gut hormones. Within minutes of eating, GLP-1 and GIP are naturally secreted in the intestines, stimulating the release of insulin and signaling satiety (reducing “food noise”) in the brain. The hormones also delay stomach emptying by slowing down gastrointestinal transit time, Dr. Nathanson says.

Some people start to lose weight fast, others start out with a more gradual loss and see more benefits as the dose is increased over several months. 

The SURMOUNT-1 trial, published in the New England Journal of Medicine, examined the effects of tirzepatide in patients with obesity. Along with lifestyle modifications, including regular exercise and a healthy diet, study participants received weekly single-dose subcutaneous injections of 5 mg, 10 mg, 15 mg, or placebo (an inactive medicine). After 72 weeks, people who received inactive medication lost only 3.1% of their body weight, while those who received Mounjaro lost up to 21%, depending on the dosage.

Although Mounjaro is used off-label for weight loss, Zepbound (tirzepatide), also manufactured by Eli Lilly, is FDA approved for weight management as well as moderate to severe obstructive sleep apnea in adults with obesity.

Weight loss timeline

Initial results vary, with some experiencing rapid weight loss and others taking longer to see results. After 40 weeks, clinical trials showed the following weight loss by dosage:

• Placebo: 0.7 kg (1.5 lb)
• 5 mg: 7 kg (15.4 lb)
• 10 mg: 7.8 kg (17 lb)
• 15 mg: 9.5 kg (21 lb)

Maintenance effects

Once you reach the maximum dosage, you may hit a plateau or continue to lose weight gradually. After you reach your goal, it’s key to stick to a healthy diet and regular exercise routine to avoid rebound weight gain.

Factors influencing results

The following factors can affect how quickly—and how well—your body responds to Mounjaro.

• Starting dose: Although some people notice appetite suppression right away, the initial low dose helps the body adjust, which in some cases may delay noticeable weight loss or improvements in blood sugar control.
• Dosage titration: Increasing the dose over time typically results in stronger effects on appetite suppression, weight loss, and blood sugar regulation.
• Lifestyle changes: Consuming a balanced diet and engaging in regular exercise maximize weight-loss results and complement the effects of Mounjaro on blood sugar management.
• Individual metabolism: Your metabolism can affect how fast and how much weight you lose with Mounjaro as well as its effectiveness in reducing blood glucose levels.

Can you regain weight after using Mounjaro?

“Unfortunately, weight regain after stopping tirzepatide is very common,” says Dr. Nathanson. While tirzepatide can counter the physiologic mechanisms that drive weight gain, these effects are lost when the medicine is stopped. In other words, weight loss from Mounjaro may not be permanent. 

Developing healthy dietary and exercise modifications can help sustain tirzepatide’s results to a degree, but weight gain may still occur after stopping the medication. The exact duration of treatment with Mounjaro can vary based on your individual health needs and treatment goals. 

In a trial investigating the effects of sustained treatment with tirzepatide, individuals who remained on the medication after the initial 36-week period (with an average weight loss of 20.9% during the first 36 weeks) achieved an additional 5.5% weight reduction after another 52 weeks. On the flip side, patients who were given a placebo rather than tirzepatide (despite maintaining a healthy diet and exercise regimen) experienced a 14% weight gain. “The data suggests that suddenly stopping the medication after achieving a goal weight is a recipe for weight regain,” Dr. Nathanson says. 

Many providers and patients have been experimenting with protocols for weight management or maintenance, such as reducing dosages or spacing doses, but research and trials are needed to support these approaches.

Preserving muscle mass through adequate protein intake and resistance training may also help keep weight off after stopping Mounjaro. “We know that maintaining adequate muscle mass affects the metabolism in a way that prevents weight regain,” Dr. Nathanson explains. “Therefore, many of us are optimistic that there may be a pathway for successfully maintaining weight after eventually stopping the medication.” 

Does Mounjaro work better than Ozempic?

In a trial, tirzepatide was slightly more effective than semaglutide (the active ingredient in brand-name Ozempic) for managing blood glucose levels.

Studies investigating the effectiveness of semaglutide (Ozempic, Wegovy) and tirzepatide for weight loss have shown that tirzepatide (Mounjaro or Zepbound) may be more effective.

According to one study, individuals who received a once-weekly injection of Wegovy (the semaglutide formulation FDA-approved for weight loss) experienced an average weight loss of 15% after 68 weeks. Results from the SURMOUNT-1 study showed that individuals who used tirzepatide lost an average of 20.9% of their body weight at 72 weeks. 

According to Dr. Nathanson, both medications have a similar side effect profile, with gastrointestinal side effects like abdominal pain, nausea, diarrhea, or constipation being the most common.

RELATED: Mounjaro vs. Ozempic

The bottom line

Mounjaro starts working immediately, but it may take several weeks for noticeable changes in your blood sugar. For weight loss, Mounjaro can affect appetite immediately. Weight loss typically begins within the first four weeks, with significant weight loss over 72 weeks. 

Before taking Mounjaro to lose weight, consult a healthcare professional for medical advice and to ensure it’s the right medication for you.