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The hypoglycemic drug Tirzepatide is a novel dual agonist of the glucagon-like peptide-1 (GLP-1) receptor and the glucose-dependent insulinotropic polypeptide (GIP, also known as gastric inhibitory peptide) receptor, administered once weekly. Both GLP-1 and GIP are incretins, peptides secreted by the gastrointestinal mucosa. GLP-1 binds to receptors on pancreatic cells to stimulate insulin secretion, thereby lowering blood sugar levels, and also delays gastric emptying and suppresses appetite, aiding in weight control. GIP, on the other hand, inhibits gastric acid and pepsin secretion, stimulates insulin release, and suppresses gastric motility and emptying, complementing the effects of GLP-1 receptor agonists. Tirzepatide integrates the insulinotropic effects of both incretins into a single molecule, representing a new class of drugs for the treatment of type 2 diabetes. This molecule consists of a 39-amino acid peptide backbone with a side chain at the Lys20 residue. Among the 39 amino acids, 37 are naturally occurring (or encoded), while two are non-natural, specifically the non-coded aminoisobutyric acid residues at positions 2 and 13.

Uses

Tirzepatide has a sequence similar to semaglutide, with a lysine side chain modified with PEG, which serves as a functional group for the peptide and enhances its water solubility. Its primary physiological function is as a dual agonist of the GIP and GLP-1 receptors, and it is being developed for the treatment of type 2 diabetes, currently in clinical trials.

Safety

The safety profile of Tirzepatide is similar to other incretin-based drugs. A meta-analysis including 7 randomized controlled trials showed that gastrointestinal reactions (such as nausea, diarrhea, and constipation) were significantly higher with Tirzepatide compared to placebo, but most were mild to moderate. Other adverse effects, particularly hypoglycemia, showed no significant difference between the groups. However, due to its relatively recent introduction, the actual safety profile requires further post-marketing surveillance.

Efficacy in Blood Sugar Reduction and Weight Loss

The SURPASS studies are a series of large-scale randomized controlled trials designed to evaluate the efficacy and safety of Tirzepatide in patients with type 2 diabetes (T2DM). Among these, the SURPASS-2 trial, which compared Tirzepatide head-to-head with semaglutide, yielded the most promising results. This study compared Tirzepatide at doses of 5 mg (n=470), 10 mg (n=469), and 15 mg (n=469) with semaglutide at 1 mg (n=468). The results showed that, compared to baseline HbA1c levels (8.3%), Tirzepatide reduced HbA1c by an average of 2.0%, 2.2%, and 2.3%, respectively, while semaglutide reduced it by 1.9%. In terms of weight loss, compared to baseline weight (207 lbs), Tirzepatide led to average weight reductions of 17 lbs, 21 lbs, and 25 lbs, respectively, compared to 13 lbs with semaglutide. This trial demonstrated that Tirzepatide outperformed semaglutide in both blood sugar reduction and weight loss.

Another large-scale study enrolled 2,539 adults with at least one obesity-related complication (excluding diabetes) and a body mass index (BMI) ≥30 kg/m² or ≥27 kg/m². Participants were randomly assigned in equal proportions to Tirzepatide 5 mg, 10 mg, 15 mg, or placebo groups. The results showed that at 72 weeks, the weight reductions were 16.1 kg, 22.2 kg, 23.6 kg, and 2.4 kg, respectively. The weight loss effects of Tirzepatide were comparable to those of bariatric surgery.

Conclusion

Tirzepatide, with its sequence similar to semaglutide and a PEG-modified lysine side chain that enhances water solubility, functions as a dual agonist of the GIP and GLP-1 receptors. It is currently in clinical development for the treatment of type 2 diabetes.