Tirzepatide

Tirzepatide is a dual GIP and GLP-1 receptor agonist developed by Eli Lilly, FDA-approved as Mounjaro for type 2 diabetes (2022) and as Zepbound for chronic weight management (2023). It is a once-weekly subcutaneous injection at doses from 2.5 mg to 15 mg, and has produced larger weight loss than semaglutide in head-to-head trials.

What is tirzepatide?

Tirzepatide is a synthetic peptide developed by Eli Lilly that acts as an agonist at two incretin receptors:

• GIP (glucose-dependent insulinotropic polypeptide) receptor
• GLP-1 (glucagon-like peptide-1) receptor

This dual mechanism distinguishes tirzepatide from single-receptor agents like semaglutide, which only activate the GLP-1 receptor. Two FDA-approved brands deliver tirzepatide:

• Mounjaro — subcutaneous injection, FDA-approved for type 2 diabetes (2022)
• Zepbound — subcutaneous injection, FDA-approved for chronic weight management (2023)

Both are administered as a once-weekly subcutaneous injection at doses titrated from 2.5 mg up to a maximum of 15 mg.

How does tirzepatide work?

The dual GIP/GLP-1 mechanism produces additive effects on:

• Glucose-dependent insulin secretion
• Glucagon suppression
• Gastric emptying delay
• Central appetite suppression
• Adipose tissue handling and energy expenditure (the GIP component appears to add metabolic effects beyond pure GLP-1 agonism)

The SURMOUNT clinical trial program established weight management efficacy. Jastreboff et al., 2022, NEJM (SURMOUNT-1) reported mean weight loss of approximately 22.5% of baseline body weight at 15 mg/week over 72 weeks, vs. 2.4% with placebo. The 2024 SURMOUNT-5 head-to-head trial showed tirzepatide produced significantly greater weight loss than semaglutide.

Why tirzepatide matters for nutrition

Tirzepatide produces larger calorie reductions than semaglutide, often 25-35%. Nutrition priorities are similar but more pressing:

• Protein — 1.2-1.6 g/kg/day, protein-forward meals
• Resistance training — to preserve lean mass during rapid weight loss
• Hydration / electrolytes
• Micronutrient sufficiency — at sustained low intake, multivitamin and B12 supplementation is often warranted

Common side effects mirror the GLP-1 class: nausea, vomiting, diarrhea, constipation, fatigue, and reflux. Rare but serious: pancreatitis, gallbladder events. Same thyroid C-cell tumor boxed warning as other GLP-1 RAs.

This is general educational information, not medical advice. Consult your physician before initiating, stopping, or changing tirzepatide therapy. Prescribing decisions, contraindications, and monitoring belong to your clinician.

See Mounjaro for brand specifics, semaglutide for comparison, and GLP-1 receptor agonist for class context.