Obesity has reached epidemic proportions in most of the developed world. This is not an exaggeration, considering nearly 40% of American adults are obese and 70% of those aged 20 and over are overweight, putting them at considerable risk of developing cancer and cardiovascular disease. While there are now many weight loss programs and drugs available on the market, one of the most promising treatments recently passed a large clinical trial with amazing results. Patients lost 24 kilograms (52 pounds) on average when using the highest dose of tirzepatide, a new drug that suppresses appetite by mimicking natural hunger-blocking hormones released by the human body after we eat a meal.

Your appetite is controlled by chemical messengers flowing through your blood. Since finding food to generate energy is essential to all living organisms, it’s not surprising that the human body has a complex system to control food intake, driven by hormones.

When the body needs calories, the gut releases the hormone ghrelin which makes us feel hungry. After eating a meal, the body produces less of the hunger hormone, while fat tissues and the stomach release hormones like PYY, GLP-1, and leptin to make us feel satiated. This dynamic interplay of chemical messages coordinates our eating behavior and food choices.

These hormones can also make life miserable for those seeking to lose a lot of weight. Following weight loss, the levels of satiety hormones decrease while the levels of hunger hormones increase, leading to a persistent feeling of hunger, reduced feelings of fullness, and slower burning of calories. This imbalance can last for many months and up to years until the body gets used to its new weight baseline. Bearing this in mind, it’s not that surprising that 8 out of 10 people on a diet end up regaining their lost weight in the long run.

To address this major roadblock in people’s weight loss journey, pharmaceutical giant Lily developed tirzepatide, which mimics the effects of GLP-1 and GIP, hormones naturally released by the human gut when we’re full after a meal. By making people feel less hungry, their calorie intake is greatly reduced, leading to weight loss.

The drug was tested on a large sample of 2,500 volunteers in nine countries, who had an average weight of 105 kilograms (230 pounds). Each participant self-administered a weekly injection of tirzepatide at low, medium, and high doses or a placebo for 72 weeks. The participants did not know which dose they were assigned to or whether they were given a placebo.

At the highest dose, the participants lost 24 kilograms (52 pounds) on average, equivalent to a 22.5% reduction in body mass. At low and medium doses, the participants lost 16 kilograms (35 pounds) or 16% of body mass and 22 kilograms (49 pounds) or 21.4% of body mass, respectively. By contrast, those who were given a placebo only lost 2 kilograms (5 pounds), equivalent to just 2.4% of their body mass.

The most common side effects were generally mild to moderate, depending on the dose, and included nausea, diarrhea, vomiting, and constipation.

“Obesity is a chronic disease that often does not receive the same standard of care as other conditions, despite its impact on physical, psychological and metabolic health, which can include increased risk of hypertension, heart disease, cancer and decreased survival,” said Louis J. Aronne, director of the Comprehensive Weight Control Center, and one of the co-authors of the study. “Tirzepatide delivered impressive body weight reductions in SURMOUNT-1, which could represent an important step forward for helping the patient and physician partnership treat this complex disease.”

Tirzepatide is in phase 3 development for adults with obesity or overweight with weight-related comorbidity and is currently under regulatory review as a treatment for adults with type 2 diabetes. There are three more clinical trials whose results are anticipated for 2023. If all goes well, the drug could become available on the market a few years later.