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Tirzepatide shown to be effective weight loss drug in phase III clinical trial

A clinical trial assessing the efficacy of tirzepatide showed the drug to be effective in significantly reducing body weight in obese patients when compared to patients who received a placebo treatment (-16.1kg .vs. -2.4kg).

Obesity is one of the leading public health issues in the United States. Recent studies estimate that nearly 42% of American adults, which accounts for over 70 million people, are considered obese.

Obesity, or the accumulation of excessive amounts of body fat, can be attributed to a variety of different factors. Lifestyle choices, medical conditions, medications, and genetics can all contribute to increases in body fat.

A study reporting on a phase three (3) clinical trial assessing the outcomes following tirzepatide (Mounjaro™) use, showed the medication to be highly effective for weight reduction. 

The clinical trial consisted of 2539 patients who were randomly assigned to receive either a placebo treatment or 5-mg, 10-mg or 15-mg of subcutaneous Tirzepatide. At week 72,  the average change in body weight between the three tirzepatide groups was -16% (95% CI, −16.8 to −15.2), with an average weight reduction of 16.1 kg (35.5 lb). The placebo group resulted in a -2.4% body weight reduction, with an average weight reduction of 2.4 kg (5.3 lb).

All of the treatment groups had over 85% of participants finish the trial with a 5% weight reduction or more (35% with placebo). The 10-mg and 15-mg groups had 50% and 57% of participants, respectively, finish the trial with a 20% weight reduction or more (3% with placebo).

The authors state, “The mean age of the participants was 44.9 years; most were female (67.5%) and White (70.6%); the mean body weight was 104.8 kg, the mean BMI was 38.0, and the mean waist circumference was 114.1 cm; 94.5% of the participants had a BMI of 30 or higher.”

Adverse effects were reported in 81.8% of patients, however, most adverse effects were reported as mild to moderate in severity and were typically gastrointestinal in nature (ie. nausea, constipation, cramping). The placebo group reported adverse effects in 72% of participants. Serious adverse effects were reported in 160 patients (6.2%), but more than a fifth of these were thought to have been complicated by SARS-CoV-2 infections (Covid-19). 

Regular counseling sessions with a certified dietician were included as part of the treatment plan for all study groups.  These sessions were intended to help patients adhere to a healthy diet, remain in a 500 calorie deficit, and regularly exercise. These lifestyle modifications likely accounted for the small reduction in body weight among patients in the placebo group.

The results of this trial were remarkably similar to patients who received bariatric surgery, which has an average weight reduction of roughly 30% at one year follow-up. The 15-mg tirzepatide group had 36.2% of patients with a weight reduction of at least 25%.


The study was published in New England Journal of Medicine on July 21st, 2022.

Abstract. Obesity is a chronic disease that results in substantial global morbidity and mortality. The efficacy and safety of tirzepatide, a novel glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 receptor agonist, in people with obesity are not known. In this phase 3 double-blind, randomized, controlled trial, we assigned 2539 adults with a body-mass index (BMI; the weight in kilograms divided by the square of the height in meters) of 30 or more, or 27 or more and at least one weight-related complication, excluding diabetes, in a 1:1:1:1 ratio to receive once-weekly, subcutaneous tirzepatide (5 mg, 10 mg, or 15 mg) or placebo for 72 weeks, including a 20-week dose-escalation period. Coprimary end points were the percentage change in weight from baseline and a weight reduction of 5% or more. The treatment-regimen estimand assessed effects regardless of treatment discontinuation in the intention-to-treat population. At baseline, the mean body weight was 104.8 kg, the mean BMI was 38.0, and 94.5% of participants had a BMI of 30 or higher. The mean percentage change in weight at week 72 was −15.0% (95% confidence interval [CI], −15.9 to −14.2) with 5-mg weekly doses of tirzepatide, −19.5% (95% CI, −20.4 to −18.5) with 10-mg doses, and −20.9% (95% CI, −21.8 to −19.9) with 15-mg doses and −3.1% (95% CI, −4.3 to −1.9) with placebo (P<0.001 for all comparisons with placebo). The percentage of participants who had weight reduction of 5% or more was 85% (95% CI, 82 to 89), 89% (95% CI, 86 to 92), and 91% (95% CI, 88 to 94) with 5 mg, 10 mg, and 15 mg of tirzepatide, respectively, and 35% (95% CI, 30 to 39) with placebo; 50% (95% CI, 46 to 54) and 57% (95% CI, 53 to 61) of participants in the 10-mg and 15-mg groups had a reduction in body weight of 20% or more, as compared with 3% (95% CI, 1 to 5) in the placebo group (P<0.001 for all comparisons with placebo). Improvements in all prespecified cardiometabolic measures were observed with tirzepatide. The most common adverse events with tirzepatide were gastrointestinal, and most were mild to moderate in severity, occurring primarily during dose escalation. Adverse events caused treatment discontinuation in 4.3%, 7.1%, 6.2%, and 2.6% of participants receiving 5-mg, 10-mg, and 15-mg tirzepatide doses and placebo, respectively. In this 72-week trial in participants with obesity, 5 mg, 10 mg, or 15 mg of tirzepatide once weekly provided substantial and sustained reductions in body weight. (Supported by Eli Lilly; SURMOUNT-1 ClinicalTrials.gov number, NCT04184622. opens in new tab.)

Jastreboff AM, Aronne LJ, Ahmad NN, Wharton S, Connery L, Alves B, Kiyosue A, Zhang S, Liu B, Bunck MC, Stefanski A; SURMOUNT-1 Investigators. Tirzepatide Once Weekly for the Treatment of Obesity. N Engl J Med. 2022 Jul 21;387(3):205-216. doi: 10.1056/NEJMoa2206038. Epub 2022 Jun 4. PMID: 35658024.

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