Tirzepatide (Mounjaro)
Mounjaro · Tirz · Zepbound
Dual GIP/GLP-1 agonist for weight loss and diabetes; weekly injection, strong efficacy.
Key takeaways
- First approved dual GIP/GLP-1 agonist — up to 22.5% body-weight reduction at the 15 mg dose in the SURMOUNT-1 trial.
- Once-weekly subcutaneous injection; roughly 5-day half-life, steady state in about 4 weeks.
- Start at 2.5 mg weekly and escalate every 4 weeks (2.5 → 5 → 7.5 → 10 → 12.5 → 15 mg) to manage GI side effects.
- FDA-approved (Mounjaro for T2D, Zepbound for weight management) with cardiovascular outcomes data.
Overview
What it is
Tirzepatide (Mounjaro, Zepbound) is the first approved dual GIP and GLP-1 receptor agonist, developed for type 2 diabetes and chronic weight management. It mimics two incretin hormones: GLP-1 (slows gastric emptying, suppresses appetite, stimulates insulin) and GIP (improves insulin sensitivity, reduces nausea). The dual mechanism produces greater weight loss than single GLP-1 agonists: 22.5% mean body-weight reduction at the 15 mg dose in SURMOUNT-1.
Pharmacokinetics
Its roughly 5-day half-life enables once-weekly subcutaneous dosing, with steady state reached after about 4 weeks. The label titration starts at 2.5 mg and escalates every 4 weeks up to 15 mg to manage dose-dependent GI side effects (nausea, vomiting, diarrhea).
What the evidence says
This is one of the best-evidenced compounds in the dataset: FDA-approved with large phase 3 RCTs and cardiovascular outcomes data. The main caveat from SURMOUNT-4 is substantial weight regain after discontinuation; it manages a chronic condition rather than curing it.
Reported dosing protocols
Protocols reported in research literature and clinic/community use — informational context, not a dosing recommendation.
| Use case | Dose | Route | Frequency | Duration |
|---|---|---|---|---|
| T2D / weight management (label) | 2.5 mg start, escalate q4wk to 15 mg max | SubQ | Once weekly | Chronic |
Pharmacokinetic summary
- Model tier
- Advanced (t½ + Cmax + Tmax + F)
- Half-life
- 4.9 days
- Cmax
- 5826.67 nmol/L
- Tmax
- 1.5 days
- Bioavailability
- 80%
- Typical dose
- 2.5–15 mg
Frequently asked questions
Tirzepatide vs semaglutide — what's the difference?
Semaglutide targets GLP-1 only; tirzepatide adds GIP receptor activity on top. Head-to-head and across-trial data show greater average weight loss with tirzepatide (22.5% vs ~15% at max doses), with a similar GI side-effect profile.
Why does tirzepatide start at only 2.5 mg?
The 2.5 mg starting dose exists for tolerability, not efficacy. Gastrointestinal side effects (nausea, vomiting, diarrhea) are dose-dependent, so the label escalates every 4 weeks to let the gut adapt before each increase.
What happens when you stop tirzepatide?
The SURMOUNT-4 withdrawal data shows substantial weight regain after discontinuation — incretin-based drugs manage a chronic condition rather than cure it. Appetite and gastric-emptying effects reverse as the drug clears (about 4 weeks given the 5-day half-life).
References
- PMC tirzepatide PK
- Jastreboff et al., NEJM 2022 — SURMOUNT-1 — Phase 3 RCT: 20.9–22.5% mean weight reduction at 10–15 mg over 72 weeks.
- FDA prescribing information (Mounjaro/Zepbound) — Label dosing schedule and titration steps.
Related compounds
Semaglutide Injection (Ozempic/Wegovy)
Long-acting GLP-1 receptor agonist for type 2 diabetes and weight loss; weekly injection.
Semaglutide Oral (Rybelsus)
Oral semaglutide with very low bioavailability; taken fasting.
Retatrutide
Triple-agonist (GLP-1/GIP/glucagon) investigational peptide; very potent weight loss.
Protocols featuring Tirzepatide (Mounjaro)
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