Tirzepatide 20 mg

What is tirzepatid?

Tirzepatid is a synthetic peptide with dual incretin activity — the molecule activates both the GIP receptor (gastric inhibitory polypeptide / glucose-dependent insulinotropic polypeptide) and the GLP-1 receptor (glucagon-like peptide-1) at the same time. It is one of the first molecules in a new pharmacological class called twincretins and represents a structural evolution from the single agonists semaglutide and liraglutide. Tirzepatide consists of 39 amino acids in a linear chain, modified with a C20 fatty acid side chain that binds to serum albumin, thereby extending the plasma half-life to approximately five days — a pharmacokinetic profile that allows for weekly administration.

Tirzepatid was developed by Eli Lilly and was first approved by the FDA in May 2022 under the trade name Mounjaro for the treatment of type 2 diabetes. In November 2023, the same molecule was approved under the trade name Zepbound for the treatment of overweight and obesity in adults with BMI ≥30 or BMI ≥27 in combination with weight-related comorbidities. The European approval process through the EMA followed shortly thereafter. The pivotal clinical trials are part of the SURPASS program (type 2 diabetes) and the SURMOUNT program (obesity).

Presentation 20 mg corresponds to the highest approved maintenance dose and is used after a stepwise up-titration starting at lower levels to reduce gastrointestinal side effects during the initial phase. The package is available in the form of pre-filled injection pens or vials intended for subcutaneous administration once a week.

How does tirzepatid work?

Tirzepatid simultaneously binds to two G protein-coupled receptors that are both central to glucose homeostasis — the GIP receptor and the GLP-1 receptor. The activation of these receptors triggers formation of cAMP via the Gs protein, which in turn activates protein kinase A and Epac-mediated signaling. The effects are complementary and synergistic on several levels.

On the beta cells of the pancreas, both receptors stimulate glucose-dependent insulin secretion — that is, insulin is released only when blood sugar is elevated, which is an important pharmacokinetic difference to sulfonylureas and reduces the risk of hypoglycemia. Glucagon secretion from the alpha cells is dampened via the GLP-1 receptor, which contributes to lowered fasting blood sugar. In the stomach, GLP-1 receptor activation slows gastric emptying, which reduces postprandial glucose peaks and contributes to early satiety.

Central nervous influence is central to weight reduction. The GLP-1 and GIP receptors in the hypothalamus, in the nucleus tractus solitarii and in the area postrema mediate satiety signals and suppress appetite. The brain's reward system is also affected in ways that reduce cravings for particularly energy-rich foods. In comparative studies, the double agonism has produced a greater effect on both HbA1c and body weight than single agonists, a finding that is interpreted as synergy between the two receptor pathways.

What can tirzepatid potentially affect?

In pharmacological studies from the SURPASS and SURMOUNT programs as well as in post-marketing data, several physiological systems in which tirzepatid leaves an imprint reappear:

• Glucose homeostasis — lowered levels of HbA1c, fasting glucose and postprandial glucose via glucose-dependent insulin secretion and suppressed glucagon production.

• Body weight and body composition — strong reductions in fat mass and total body weight, documented between 15 and 22 percent at the highest doses studied in SURMOUNT-1.

• Appetite regulation and satiety — central influence in the hypothalamus and brainstem reduces appetite, delays gastric emptying and prolongs the feeling of satiety.

• Lipid metabolism — decreased levels of triglycerides, LDL and total cholesterol and increased HDL in clinical studies.

• Blood pressure and cardiovascular markers — moderate reduction in blood pressure as well as improvement in some inflammatory and cardiovascular biomarkers documented in ongoing follow-up studies.

• Hepatic and renal function — reduced steatosis in non-alcoholic fatty liver disease and improved albuminuria in incipient diabetic nephropathy have been observed in exploratory analyses.

Potential side effects of tirzepatid

The side effect profile of tirzepatid has been extensively documented in the SURPASS and SURMOUNT programs as well as in post-marketing reporting after introduction in 2022. The profile is dominated by gastrointestinal side effects, mainly during the up-titration phase, and usually decreases with time. More rare but serious side effects occur and require attention during clinical follow-up.

• Gastrointestinal — nausea, vomiting, diarrhea, constipation, and abdominal pain are the most common side effects. The symptoms are typically most pronounced during the first weeks and with each dose increase, and decrease in intensity over time.

• Pancreatitis — acute pancreatitis has been reported. The risk increase is small, but the occurrence is a central observation in treatment, especially in patients with previous pancreatitis or gallstone disease.

• Gallbladder and biliary tract — cholelithiasis and cholecystitis are documented, likely linked to the rapid weight loss rather than a direct molecular effect.

• Thyroid C-cells — in animal studies, medullary thyroid cancer has been observed in rats, warranting caution for C-cell tumors in humans, although human relevance is questionable.

• Hypoglycaemia — the risk is low with monotherapy but increases significantly in combination with insulin or sulfonylureas, which is why dose adjustment of additional treatment is necessary.

• Local reactions — redness, itching and skin reactions at the injection site, usually mild and transient.

• Dehydration and renal function — severe and prolonged gastrointestinal side effects can cause dehydration and, in rare cases, acute renal involvement, mainly in predisposed individuals.

• Visual effects — diabetic retinopathy may temporarily worsen with rapid glucose control, a phenomenon also documented with other effective glucose-lowering drugs.

The overall side effect picture of tirzepatide — gastrointestinal effects, rare but serious reactions in the pancreas and biliary tract, as well as a theoretical C-cell tumor risk — means that clinical use is based on close monitoring of symptoms, weight development and relevant laboratory parameters (HbA1c, lipid status, liver and kidney function, calcitonin in at-risk individuals).