Tirzepatide: How It Works, What It Costs, and the Compounding Question

The Short Answer

Tirzepatide is a once-weekly injectable that acts on two gut hormone receptors rather than one, which is why it has outperformed every other obesity medication in head-to-head testing. At the highest dose, adults lost 22.5% of their body weight over 72 weeks. Buying it direct from Eli Lilly costs $299 to $449 a month depending on dose — with a refill condition that can more than double that if you miss it.

What is tirzepatide?

Tirzepatide is a dual GIP and GLP-1 receptor agonist. Where semaglutide mimics one gut hormone, tirzepatide mimics two.

GLP-1 is the one most people have heard of: released after eating, it prompts insulin, slows digestion and signals fullness. GIP — glucose-dependent insulinotropic polypeptide — is a second incretin hormone released from a different part of the gut, and its role in appetite and fat metabolism is less completely understood than GLP-1's.

Like semaglutide, tirzepatide is a peptide engineered to last days instead of minutes, which is why it is a weekly injection.

Why does acting on two receptors matter?

Because in practice it produces more weight loss, and that shows up in direct comparison rather than only in cross-trial arithmetic.

SURMOUNT-5 put the two drugs head to head over 72 weeks in 751 participants. Tirzepatide produced 20.2% mean weight loss against semaglutide's 13.7% — a 47% greater relative reduction. On the harder thresholds the gap widens:

What that does not settle is which one is right for you. Individual response varies widely, side-effect tolerance varies more, and cost and coverage often decide it before efficacy does. Our tirzepatide vs. semaglutide guide works through the cases where the drug with the lower average is still the better choice.

Which brands contain tirzepatide?

As with Ozempic and Wegovy, these are the same drug under two names with different approved uses and dosing. A prescriber treating obesity should be writing for Zepbound. Zepbound is also the only one of the pair approved for obstructive sleep apnoea in adults with obesity.

What does the evidence show?

SURMOUNT-1 followed 2,539 adults with obesity, or overweight with a weight-related condition, for 72 weeks:

Nearly two thirds of participants on the highest dose lost at least a fifth of their body weight. That is the number that changed how obesity medicine talks about what is achievable without surgery.

Two caveats worth carrying. These are trial averages under trial conditions, with structured support most patients do not get. And weight returns when the medication stops — the same pattern seen with semaglutide. Plan for a long-term treatment, not a course.

What are the side effects?

The profile closely resembles semaglutide's. Gastrointestinal effects dominate — nausea most commonly, then vomiting, diarrhoea and constipation, concentrated in the early weeks and after each dose step. Titration is deliberately slow for this reason.

The serious ones: pancreatitis has been reported, and severe persistent abdominal pain warrants a call rather than a wait. Gallbladder problems occur at somewhat higher rates. Tirzepatide carries a boxed warning for thyroid C-cell tumours based on rodent studies, and it is contraindicated in anyone with a personal or family history of medullary thyroid carcinoma or MEN 2 syndrome. It should not be used in pregnancy. One difference from semaglutide worth flagging: tirzepatide may reduce the effectiveness of oral contraceptives around dose increases, so contraception is a conversation to have before starting rather than after.

Fuller detail in Weight Loss Medications Explained.

Is compounded tirzepatide still legal?

The window has largely closed, and tirzepatide closed first.

The FDA declared the tirzepatide shortage resolved on December 19, 2024 — two months ahead of semaglutide. State-licensed pharmacies had until February 18, 2025 to wind down and outsourcing facilities until March 19, 2025. With the drug off the shortage list, compounded versions became "essentially a copy" of an available commercial product, which limits compounding to a documented clinical need for an individual patient.

On April 30, 2026 the FDA proposed excluding tirzepatide from the 503B bulks list, finding "no clinical need for outsourcing facilities to compound these drugs from bulk substances." Public comment closed June 29, 2026.

Compounded tirzepatide is still advertised. In March 2026 the FDA sent warning letters to 30 telehealth companies over compounded GLP-1 marketing — objecting to "claims implying sameness with FDA-approved products" and to "obscuring product sourcing by advertising drug products branded with the telehealth firm's name." No companies were named. Ask any provider which pharmacy fills the prescription and on what legal basis. A provider who will not name the pharmacy has told you something.

What does tirzepatide cost?

Eli Lilly sells Zepbound single-dose vials direct at published prices, announced December 1, 2025:

Read the refill condition before you budget. Those prices apply when a prescription is refilled within 45 days of the previous delivery. Miss that window and the two highest doses revert to $849/month at 12.5 mg and $1,049/month at 15 mg. A supply gap, a holiday, or a slow prior authorisation can trigger it.

With commercial insurance covering obesity treatment, Lilly's savings card brings the cost down substantially. Eligible Medicare Part D beneficiaries can pay $50 a month through the CMS Medicare GLP-1 Bridge, running July 1, 2026 to December 31, 2027.

Telehealth platforms that carry tirzepatide run $99 to $548 a month across the providers we track, medication usually included — though not always, so check. Mochi Health, for instance, charges a $79 membership with compounded tirzepatide priced separately from $90. Full comparison in the GLP-1 Price Guide and the cost calculator.

Where to go next

Read the semaglutide guide, compare them directly in tirzepatide vs. semaglutide, or browse providers and clinics prescribing tirzepatide.

Sources

• Eli Lilly — SURMOUNT-1 results published in NEJM — 2,539 participants, 72 weeks, 16.0%/21.4%/22.5% by dose vs 2.4% placebo.
• Eli Lilly — SURMOUNT-5 head-to-head results — May 11, 2025; 751 participants, tirzepatide 20.2% vs semaglutide 13.7%.
• Eli Lilly — Lilly lowers the price of Zepbound single-dose vials — December 1, 2025, per-dose prices and the 45-day refill condition.
• FDA — FDA clarifies policies for compounders as national GLP-1 supply begins to stabilize — tirzepatide shortage resolved December 19, 2024 and wind-down deadlines.
• FDA — FDA Proposes to Exclude Semaglutide, Tirzepatide, and Liraglutide on 503B Bulks List — April 30, 2026.
• FDA — FDA warns 30 telehealth companies against illegal marketing of compounded GLP-1s — March 3, 2026.
• CMS — Medicare GLP-1 Bridge
• Side effect, boxed warning, pregnancy and oral-contraceptive statements are drawn from the FDA prescribing information for Zepbound and Mounjaro.

*Every dated claim above was verified against the source linked beside it on the date shown at the top of this guide. This is not medical advice — talk to a licensed clinician before starting or changing any treatment.*