tirzepatide

tirzepatide, synthetic antidiabetic drug used in the treatment of type 2 diabetes. Tirzepatide is the first drug in a class of agents known as dual glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP) receptor agonists. Because both GLP-1 and GIP are so-called incretin hormones (substances produced in the body that stimulate beta cells in the pancreas to release insulin), the drug is sometimes also referred to as a “twincretin.”

Tirzepatide was approved for the treatment of type 2 diabetes by the U.S. Food and Drug Administration (FDA) in 2022, under the trade name Mounjaro. It is administered via injection under the skin once per week.

Mechanism of action

Insulin is a hormone that regulates the level of glucose (sugar) in the blood. It is secreted by beta cells in the islets of Langerhans in the pancreas when blood glucose levels increase, such as after a meal. When blood glucose levels decrease, insulin secretion stops, and glucagon, another hormone produced by cells in the islets of Langerhans, stimulates the liver to release glucose into the blood.

In type 2 diabetes, however, cells and tissues become resistant to insulin or the body is unable to produce sufficient amounts of insulin, resulting in hyperglycemia (abnormally high blood glucose). The condition is also associated with reduced effects of the GLP-1 and GIP incretin hormones. Because the incretins play a key role in augmenting insulin secretion following nutrient intake, their reduced activity has a further impact on blood glucose dysregulation. Type 2 diabetes is strongly associated with obesity, and, thus, blood glucose levels often can be controlled through diet and exercise. Nonetheless, some persons with the condition require more-intensive treatment with medication.

Tirzepatide contains two polypeptides, one of which is an analog of GLP-1 and the other an analog of GIP. These analogs bind to and activate their corresponding receptors, essentially mimicking the effects of the naturally occurring incretins. In particular, tirzepatide activation of GLP-1 receptors improves glucose-mediated insulin secretion and decreases secretion of glucagon. Tirzepatide activation of GIP receptors augments insulin sensitivity and secretion and thereby helps reinforce the mechanisms regulating blood glucose levels. Owing to the drug’s additional effects, such as delayed gastric emptying and increased satiety after nutrient consumption, its use is further associated with reduced food intake and weight loss.

Side effects

The use of tirzepatide is associated primarily with gastrointestinal side effects, such as abdominal pain, constipation, decreased appetite, diarrhea, nausea, and vomiting. Less common side effects include heartburn, accelerated heart rate, fever, swelling of the face, and itchy or red skin. The use of tirzepatide is limited in certain individuals, owing to contraindications. Such individuals include those already taking GLP-1 agonists (e.g., liraglutide or semaglutide) and persons who are at risk for certain thyroid-related cancers (e.g., medullary thyroid carcinoma) or who have a history of multiple endocrine neoplasia syndrome type 2, since tirzepatide could theoretically increase the chances of developing such tumors in persons with preexisting risk factors.