Tirzepatide Explained: How GIP and GLP-1 Receptor Activity Works

Peptide Library

Tirzepatide is a peptide medicine with activity at two hormone receptors. Understanding those targets helps explain how it differs from semaglutide and from investigational compounds such as retatrutide. [1]

What is tirzepatide?

Tirzepatide activates glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptors. Both are involved in metabolic signalling. Its effects include glucose-dependent insulin secretion and changes in appetite and food intake. Receptor activity is a description of how the molecule works, not a guarantee of a particular result. [2]

What does clinical evidence show?

In SURMOUNT-5, adults with obesity without type 2 diabetes had average weight reductions of 20.2% with tirzepatide and 13.7% with semaglutide over 72 weeks. These results concern a specified open-label trial comparison, not every formulation or patient. [4]

Approval is product-specific

Aspen announced a SAHPRA-approved chronic weight-management indication for Mounjaro in October 2025, following its South African introduction for type 2 diabetes. The current South African professional information remains the reference for the authorised product’s exact indications and conditions of use. An ingredient name on another pen or vial does not establish equivalent registration. [3]

Safety belongs in the discussion

The Mounjaro label lists common gastrointestinal effects, including nausea, vomiting, diarrhoea and constipation. It also describes important precautions concerning pancreatitis, gallbladder disease, dehydration-related kidney problems and low blood glucose when combined with certain diabetes medicines. The US label includes a boxed thyroid C-cell tumour warning based on animal findings and contraindications relating to medullary thyroid carcinoma and MEN2. These points require clinical assessment, not self-selection from a comparison chart. [1]

Why the actual product matters

SAHPRA’s 2026 enforcement notice highlights the distinction between authorised medicines and unlawfully manufactured or distributed unregistered formulations. Study results for a registered medicine do not validate every product carrying the same active-ingredient name. Documentation, manufacturing quality and the authorised formulation are part of the evidence picture. [5]

Frequently asked questions

Is tirzepatide just another name for semaglutide?

No. Tirzepatide activates GIP and GLP-1 receptors; semaglutide activates GLP-1 receptors.

Is Mounjaro the ingredient name?

No. Mounjaro is a medicine brand; tirzepatide is its active ingredient.

Is this article a treatment schedule?

No. Treatment selection and dosing depend on the prescribed product and a clinician’s assessment.

Explore related articles

Sources

  1. DailyMed: current Mounjaro prescribing information
  2. SAHPRA: tirzepatide professional information — mechanism
  3. Aspen corporate announcement: SAHPRA weight-management indication, October 2025
  4. Aronne et al., 2025: SURMOUNT-5 head-to-head trial
  5. SAHPRA: enforcement concerning unregistered GLP-1/GIP products, May 2026

Research checked: 11 October 2026. Educational information; not a diagnosis, prescription or dosing guide. Prepared for SkyCor with AI-assisted research and drafting; not independently medically reviewed. Approval information relates to the named products and jurisdictions, not every product carrying the same ingredient name.

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