Tirzepatide
Mounjaro (T2D) · Zepbound (weight management)
Tirzepatide is an FDA-approved dual GIP/GLP-1 receptor agonist — the first in its class to target both incretin receptors simultaneously. Marketed as Mounjaro for type 2 diabetes and Zepbound for chronic weight management, it has demonstrated the strongest weight loss results of any approved GLP-1 class medication in clinical trials. Tirzepatide is administered as a once-weekly subcutaneous injection via a single-dose auto-injector pen.
Quick Reference
Dose Titration Schedule
Tirzepatide follows a fixed titration schedule. Each dose level is maintained for at least 4 weeks before increasing. The goal is to reach the lowest effective dose that provides adequate glycemic control or weight loss while minimizing GI side effects.
Tier 1 — Initiation
2.5 mg
Once weekly
Weeks 1–4
Starting dose for all patients. Not considered a therapeutic dose — its purpose is GI tolerability. Expect minimal weight loss at this level.
Tier 2 — First Therapeutic Dose
5 mg
Once weekly
Weeks 5–8
First therapeutic dose. Many patients begin to see appetite suppression and early weight loss. Can be maintained long-term if effective.
Tier 3 — Intermediate
7.5 mg
Once weekly
Weeks 9–12
Intermediate step. Increased efficacy for weight loss and A1C reduction. GI side effects may temporarily increase with each titration.
Tier 4 — Standard High
10 mg
Once weekly
Weeks 13–16
Strong therapeutic dose. Many patients stabilize here. Clinical trials showed significant weight loss and A1C improvement at this level.
Tier 5 — Escalation
12.5 mg
Once weekly
Weeks 17–20
Higher dose for patients who need additional efficacy. Monitor closely for GI tolerability before advancing to maximum dose.
Tier 6 — Maximum
15 mg
Once weekly
Week 21+
Maximum approved dose. Used when lower doses provide insufficient response. SURMOUNT-1 showed the greatest weight loss at this dose (22.5% mean body weight reduction).
Injection Guide
Tirzepatide is supplied in pre-filled, single-dose auto-injector pens. No reconstitution or dose measurement is required — each pen delivers one fixed dose.
Injection Sites
- Abdomen — at least 2 inches from the navel. Most common site for self-injection
- Front of thigh — mid-thigh area with adequate subcutaneous tissue
- Upper arm — back of the arm (may require assistance for self-injection)
Rotate injection sites each week. Do not inject into areas that are tender, bruised, red, or hard. Inject on the same day each week — the day can be changed if the last dose was administered at least 3 days prior.
Auto-Injector Instructions
- Remove the pen from the refrigerator 30 minutes before use to reach room temperature.
- Inspect the solution — it should be clear and colorless to slightly yellow. Do not use if cloudy or contains particles.
- Pull off the gray base cap. Do not put the cap back on — this can damage the needle.
- Place the clear base flat against the cleaned injection site.
- Unlock and press the injection button. Hold for 10 seconds until you hear a second click.
- Remove the pen. Verify the gray plunger is visible in the window — confirming full dose delivery.
Side Effects
The most common side effects are gastrointestinal and typically occur during dose titration, improving over time. Tirzepatide carries a boxed warning for medullary thyroid carcinoma (MTC) risk based on rodent studies.
Nausea
Diarrhea
Decreased appetite
Vomiting
Constipation
Dyspepsia
Injection site reactions
Fatigue
Pancreatitis
Gallbladder events
⚠ Boxed Warning — Thyroid C-Cell Tumors
In rodent studies, tirzepatide caused thyroid C-cell tumors including medullary thyroid carcinoma (MTC). It is unknown whether tirzepatide causes thyroid C-cell tumors in humans. Contraindicated in patients with a personal or family history of MTC or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2).
Mechanism of Action
Dual Incretin Agonism
Unlike semaglutide (GLP-1 only), tirzepatide activates both the GIP and GLP-1 receptors. This dual mechanism produces additive metabolic effects: enhanced insulin secretion, reduced glucagon, slowed gastric emptying, and stronger central appetite suppression. The GIP component may also improve fat metabolism and enhance the GLP-1 pathway's effects on energy balance.
GLP-1 effects
Appetite suppression, insulin secretion, slowed gastric emptying
GIP effects
Enhanced fat metabolism, potentiated insulin response, improved lipid handling
Combined result
Superior weight loss and glycemic control vs GLP-1 alone
Research Summary
Tirzepatide has extensive Phase III clinical trial data across both type 2 diabetes (SURPASS program) and obesity (SURMOUNT program):
SURMOUNT-1: participants without T2D lost up to 22.5% of body weight at 15 mg over 72 weeks vs 3.1% placebo. The largest weight reduction seen in a Phase III GLP-1 class trial.
Jastreboff et al., 2022, N Engl J Med
SURMOUNT-2: participants with T2D and obesity lost up to 14.7% of body weight at the maximum dose over 72 weeks, with meaningful A1C reductions.
Garvey et al., 2023, Lancet
SURPASS-1 through SURPASS-5: tirzepatide consistently reduced A1C by 1.9–2.6% across trials, outperforming semaglutide 1 mg, insulin degludec, and insulin glargine.
Rosenstock et al., 2021, N Engl J Med (SURPASS-1)
SURPASS-2: tirzepatide at all doses (5, 10, 15 mg) demonstrated superior A1C reduction and weight loss vs semaglutide 1 mg in T2D patients.
Frias et al., 2021, N Engl J Med
SURPASS-CVOT: cardiovascular outcomes trial showed non-inferiority for major adverse cardiovascular events (MACE) vs dulaglutide. Additional cardiovascular benefit studies are ongoing.
Lilly, 2024, presented at ADA
Tirzepatide is FDA-approved for T2D (Mounjaro, 2022) and chronic weight management (Zepbound, 2023). All cited results are from published Phase III randomized controlled trials.
FAQ
How does tirzepatide compare to semaglutide?
Tirzepatide targets both GIP and GLP-1 receptors, while semaglutide targets GLP-1 only. In head-to-head trials (SURPASS-2), tirzepatide produced greater A1C reduction and weight loss at all dose levels compared to semaglutide 1 mg. SURMOUNT-1 showed 22.5% weight loss for tirzepatide vs ~15% for semaglutide in comparable trials.
What is the difference between Mounjaro and Zepbound?
They are the same molecule (tirzepatide) made by Eli Lilly. Mounjaro is approved for type 2 diabetes, while Zepbound is approved for chronic weight management in adults with obesity (BMI ≥30) or overweight (BMI ≥27) with at least one weight-related condition. The dosing and titration schedule are identical.
Can I use compounded tirzepatide instead of brand?
Compounded tirzepatide has been available from 503A/503B compounding pharmacies during FDA shortage periods. However, compounded versions are not FDA-approved, may vary in quality, and the FDA has moved to restrict compounding as brand supply stabilizes. Discuss options with your prescribing physician.
What if I miss a dose?
If missed within 4 days (96 hours) of the scheduled day, take it as soon as possible. If more than 4 days have passed, skip the missed dose and resume on the next scheduled injection day. Do not take two doses within 3 days of each other.
Auto-injector pen vs syringe — what is the difference?
Brand tirzepatide (Mounjaro/Zepbound) uses pre-filled single-dose auto-injector pens — no measuring, reconstitution, or syringes needed. Compounded tirzepatide typically comes in multi-dose vials requiring insulin syringes and dose calculation, similar to other research peptides.
How should I store tirzepatide?
Unopened pens: refrigerate at 2–8°C (36–46°F). Pens may be stored at room temperature (up to 30°C / 86°F) for up to 21 days if needed. Do not freeze. Protect from light. Do not use after the expiration date.
Can I drink alcohol on tirzepatide?
Alcohol is not strictly contraindicated, but it can worsen GI side effects (nausea, vomiting) and may cause unpredictable blood sugar changes, especially in T2D patients. Most prescribers recommend moderation and monitoring how you feel.
Should I exercise while on tirzepatide?
Yes. Exercise is strongly recommended to preserve lean muscle mass during weight loss. Resistance training is particularly important, as rapid weight loss from GLP-1 agonists can lead to muscle loss alongside fat loss. Adequate protein intake (0.7–1 g per pound of lean body mass) supports this.
Track your tirzepatide protocol
Log your doses, track titration progress, and monitor side effects over time.