A scientist who created Ozempic explains what the drug actually does to your brain — and why it makes people satisfied while eating less

• Ozempic and Wegovy have a direct effect on hunger signals in the brain.
• The drugs make people feel full with less food, and can change food preferences.

Now you can stick a needle in your belly, and change your brain's appetite for food.

The injectable drugs Ozempic and Wegovy, and their generic counterpart semaglutide, have been hailed as blockbuster treatments for obesity and diabetes because they can often help people lose excess weight they've struggled with for years. In many cases, patients have said these drugs are succeeding where all other diets, exercise, and medicines have failed before.

Karin Conde-Knape, senior vice president of global drug discovery at Novo Nordisk, the company that makes the drugs, says the reason why these medications have such stunning results is simple. It's because the drugs change people's brains, regulating hunger signals in a whole new way.

Ozempic and Wegovy help people feel full while eating less "because of a direct effect on satiety," Conde-Knape explained on Wednesday during CNBC's Healthy Returns Summit. Patients report feeling satisfied with less food than they would have eaten before.

In addition to quantity of food, the drug also controls "the type of food that we are craving," Conde-Knape said, by "tackling a different part of the brain that also signals through the sensations of satisfaction when you eat certain types of foods."

Patients have said Ozempic makes them less interested in formerly favorite foods, like Chick-fil-A, coffee, alcohol and Kit Kats, and more into kale and smoothies.

Ozempic does this by mimicking a compound people produce naturally in our intestines, called GLP-1. GLP-1 is a hunger-regulating hormone, and it's similar to a compound Gila monsters harbor in their venom. But GLP-1 mimicking drugs "can last longer" and "have a more durable effect" than the natural hormones, Conde-Knape said.

In addition to its effects on the brain, Ozempic also slows down digestion, and can help regulate blood sugar, by slowing the production of glucose in the liver.

The most common side effects of Ozempic include stomach cramps, nausea, and other GI issues like diarrhea, vomiting, and constipation.

Ozempic helps regulate key hunger hormones that may be out of whack in obese patients

It might seem like weight loss is a simple energy in versus energy out equation, but "the brain regulation of energy intake and output is actually quite complex," Conde-Knape said.

Most obese patients have some kind of "genetic component" that is also driving their disease, she said, and then there are likely environmental factors at work, too, which are still not well understood.

"The GLP-1 that is secreted from the intestine signals through the brain in the specific areas that actually control how much hunger we have, but also how full we feel after we have a meal," Conde-Knape added. "And in individuals that maybe are suffering more with obesity, there is a deregulation in this."

But, just like a real hormone, Ozempic won't work to control your appetite once you stop taking it, which is why many patients regain much of the weight they lost within a few months or years, once they discontinue the medication.

"We are not yet able to redefine that body-wide setpoint," Conde-Knape said. "The quest in identifying better mechanisms for obesity is not over yet."