Weight-loss drugs affect the brain in ways that help researchers understand how the body regulates weight.

Ozempic and similar drugs are transforming the world’s understanding of obesity. It isn’t so much about willpower: It’s about biology. The success of the powerful new class of diabetes and weight-loss drugs shows how important chemistry is to determining a person’s weight. The brain is the body’s chief chemist, regulating appetite and making it difficult for many people to shed pounds and keep them off. The brain determines how much fat it wants people to carry, according to years of research bolstered by the new drugs. The amount is like a setting on a dial, or what many researchers call a “set point” or “defended fat mass.” The brain maintains the dial setting or set point by regulating how much a person eats. Ozempic, its sister drug Wegovy and another, Mounjaro, lower the dial setting, or set point, in effect by acting on the brain to reduce hunger and make a person feel full sooner, some obesity researchers say. The new set point lasts as long as a patient is on the drug, they say. Patients who ate a lot before they started taking one of the drugs feel less hungry and fill up more quickly—sometimes after one slice of pizza when they once ate the whole pie. “This is not about willpower or personal choice,” said Dr. Florencia Halperin, an endocrinologist and chief medical officer of Form, a virtual medical weight-loss clinic. “This is about your brain driving behaviors.”

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