Tirzepatide may work a little better because it’s a dual receptor agonist; in addition to GLP-1, it activates receptors for GIP, another hormone involved in regulating blood sugar and appetite. But Maguire says GIP is not well understood, so it’s unclear whether adding it helps increase weight loss or whether tirzepatide is just better at activating GLP-1. “Right now we don’t have a way to figure out the biology of it,” he says.
Still, drug companies are continuing to pursue GIP as a target. Viking Pharmaceuticals is also developing a drug that activates both the GLP-1 and GIP receptors. The San Diego company is testing both an injectable and a pill. In the injectable trial, participants Lost about 15% of body weight Over 13 weeks. Early-stage trial data released in March showed that a daily pill version of Viking Lost about 5% of body weight On average, it takes just one month.
Novo Nordisk, Eli Lillyand Pfizer All are working on developing their own GLP-1 pills. Some patients prefer taking a daily pill rather than a weekly injection. The pills are easier to manufacture than the injection pens used to administer Wegovy and Zepbound. And the pens must be kept refrigerated.
“All of this makes these drugs more expensive,” said Laura Davisson, director of the weight management program at West Virginia University Health System. “If we could bring an oral medication to market, the price could go down.”
Meanwhile, Amgen thinks a less frequent dose might be more convenient for some patients: The company is working on a once-monthly injectable drug called Maritide, which also targets GLP-1 and GIP, but Maritide blocks GIP receptors rather than stimulating them. Not entirely clear Why stimulating or blocking these receptors appears to promote weight loss.
Amgen’s approach is based on studies showing that mice lacking GIP and humans with mutations in the receptor have lower body weight. Results announced in FebruaryIn early trials, people taking Maritide lost up to 14 percent or more of their body weight over 12 weeks.
Eli Lilly is trying to make a drug even more powerful than Zepbound by adding a third mechanism that plays a role in weight loss. The company is working on an investigational drug called Retatortide that targets receptors for GLP-1, GIP and glucagon, which help break down fat stores. Published last yearAfter 24 weeks, Retatortide helped participants lose more than 17% of their body weight, or 41 pounds. After 48 weeks, participants had lost an average of 24% of their body weight, or about 58 pounds — more weight loss than any other drug on the market.
“We’ve never seen results like these before in a trial of an anti-obesity drug lasting less than a year,” Ania Jastrebov, an endocrinologist and weight-management expert at the Yale School of Medicine, said at a press conference at last year’s American Diabetes Association annual meeting.
