Novo Nordisk's semaglutide is the first drug approved for the treatment of obesity that has achieved weight loss similar to bariatric surgery. Eli Lilly's tirzepatide, which works in a similar way, is expected to be approved in the coming months after it has been shown to be effective and safe in clinical trials. Other pharmaceutical multinationals are developing similar drugs to treat a disorder that in Spain affects 22% of the adult population.
The new drugs mimic the action of the GLP-1 hormone, which the human body naturally produces and has multiple effects on the body. In the pancreas, GLP-1 enhances the activity of insulin, which is why semaglutide was initially developed as a treatment for diabetes. In the digestive system, it slows down the emptying of the stomach, which makes it easier for the person to take longer to feel hungry again after eating. Even more important is the effect of GLP-1 in the brain, where it reduces appetite and increases the feeling of satiety in regions of the nervous system that regulate food intake behavior.
Semaglutide has achieved an average weight loss of 17% in people with obesity in clinical trials. An average weight loss of 21% has been recorded with tirzepatide – although the design of the clinical trials was different, so the effectiveness of the two drugs cannot be directly compared. With a third drug in a not so advanced phase of development, Eli Lilly's retatrutide, the average weight loss has reached 24%.
New anti-obesity drugs have been shown to be effective in clinical trials in which participants underwent diet and physical activity in addition to drug treatment. Therefore, GLP-1 analogs are presented as supplements to diet and physical activity, not as substitutes.
Side effects that force treatment to be discontinued are exceptional, but mild adverse effects that are bothersome are common. The most common are nausea (which affected 38% of participants in semaglutide clinical trials), vomiting (22%), diarrhea (27%) and constipation (22%). These side effects usually appear in the first few weeks of treatment and usually diminish over time. To minimize them, it is usual to start the treatment with low doses and increase them little by little over several weeks.
Since these are drugs that have been used for a short time, they could have long-term effects that are still unknown, and which could be both positive and negative.
Semaglutide is available in Spain under the trade name Ozempic for the treatment of diabetes in people with obesity. For the treatment of obesity in people without diabetes it is approved, but it has not yet started to be distributed and will have the commercial name of Wegovy. The difference between Ozempic and Wegovy is in the dose, which is a maximum of 1 milligram per week for diabetes and can reach 2.4 milligrams for obesity.
Tirzepatida, on the other hand, has been approved in Europe since last year for the treatment of diabetes under the name Mounjaro, but it is not yet available in Spain. The European Medicines Agency (EMA) is currently evaluating its approval for the treatment of obesity. The Eli Lilly company expects the EMA to announce its decision at the end of 2023 or the beginning of 2024.
There will be two options: injection and pills. Wegovy is given as a subcutaneous injection once a week. Users inject the drug themselves, usually in the abdomen or thigh, with an extremely fine, easy-to-use needle that causes no pain. For Ozempic against diabetes, in addition to the injectable version, there is already an alternative in pills that must be taken daily in the morning on an empty stomach. "There are people who prefer pills and others who prefer the injection, because that way they don't have to worry about taking the drug every day", says Andreea Ciudín, coordinator of the obesity unit at Vall d'Hebron hospital in Barcelona. Companies that are developing GLP-1 analogs for obesity are investigating injectable and also pill presentations.
The European Medicines Agency has approved Wegovy for three groups: adults with a body mass index (BMI) of more than 30 (the limit above which a person is considered obese); adults with a BMI between 27 and 30 (which is considered overweight but not obese) if they have at least one serious health problem associated with being overweight, and adolescents over 12 years of age who are obese and weigh more than 60 kilos
BMI is calculated by dividing a person's weight in kilograms by the square of their height in meters. For example, for a person of 1.80 meters and 80 kilograms, the BMI is 24.7 (which is the result of dividing 80 by 1.80, and dividing the result again by 1.80).
Wegovy is not approved for rapid weight loss nor has it been shown to be effective for this purpose. The effectiveness has been evaluated in clinical trials in which the participants have taken the drug for a minimum of eleven months, in which they have lost weight in a progressive manner.
When the treatment was stopped at the end of the clinical trials, most of the participants gained weight back. This observation suggests that, for many users, anti-obesity treatment with drugs based on the GLP-1 hormone will be longer-term, and possibly chronic.
In Spain, both semaglutide and tirzepatide are dispensed with a prescription.
"The price [of Wegovy] will be made public when we start marketing the medicine in Spain," a company spokeswoman said on Friday. "Currently we are not in a position to offer a figure". In Germany, where the drug is already on sale, the price is around 310 euros per month.
