Everything about tirzepatide, with the calculators.

01 What is tirzepatide?

Tirzepatide is a once-weekly injectable medication developed by Eli Lilly. It is the first and currently only FDA-approved drug that activates two gut-hormone receptors at once: GLP-1 (the same target as semaglutide) and GIP (a second incretin hormone). The combination produces stronger appetite suppression and better blood-sugar control than any GLP-1 monotherapy on the market.

Sold under two brand names — Mounjaro for type 2 diabetes and Zepbound for chronic weight management — both contain the identical active ingredient (tirzepatide), the same dose strengths, and the same delivery device. The only difference is the FDA label.

Outside the brand market, the same molecule is also widely available as compounded tirzepatide through state-licensed pharmacies. Compounded versions are not FDA-approved, but they are legal under section 503A/503B of the FD&C Act and are the dominant form prescribed via telehealth in 2026 because they cost roughly 70–85% less than brand vials.

02 How does tirzepatide work?

Tirzepatide is a 39-amino-acid peptide that mimics two of your gut's natural incretin hormones at once. After a weekly subcutaneous injection, it binds to and activates both the GLP-1 receptor and the GIP receptor — together, they shape three things: how hungry you feel, how fast your stomach empties, and how your pancreas releases insulin.

The dual mechanism, in plain English

• Slows stomach emptying. Food stays in the stomach longer. You feel full earlier and stay full longer between meals.
• Reduces appetite signals. GLP-1 receptors in the brain (specifically the hypothalamus and brainstem) act on the hunger circuits — reducing how much you want to eat and how often you think about food. Most patients describe a dramatic drop in "food noise."
• Improves insulin response. Both GLP-1 and GIP increase insulin release in a glucose-dependent way (only when blood sugar is high). This is why tirzepatide doesn't typically cause hypoglycemia in people without diabetes.
• GIP advantage. The GIP arm appears to enhance the weight-loss effect, possibly by improving how fat tissue handles energy. This is the part semaglutide doesn't have.

How fast does it work?

Most patients report appetite changes in the first 1–2 weeks. Real weight loss begins around week 2–4. Tirzepatide has a half-life of about 5 days, which is why a single weekly injection produces steady drug levels for the entire week. Steady-state plasma concentrations are typically reached after roughly 4 weeks at any given dose.

03 Tirzepatide for weight loss

The headline reason 791,000 people Google "tirzepatide" every month is weight loss. Below is what the SURMOUNT trials — Lilly's pivotal studies for the Zepbound indication — actually showed in adults with obesity but without type 2 diabetes.

SURMOUNT-1: Average weight loss at 72 weeks

Source: Jastreboff et al., New England Journal of Medicine, 2022 (SURMOUNT-1, n=2,539).

At the highest dose, the average participant on tirzepatide lost about 20.9% of their body weight — roughly 48 pounds in a 230-pound adult. About 57% of the 15-mg group reached ≥20% loss, and 36% reached ≥25% — outcomes previously achievable only with bariatric surgery.

SURMOUNT-2 confirmed similar (slightly smaller) results in patients with type 2 diabetes. SURMOUNT-3 showed that adding tirzepatide after a 12-week intensive lifestyle program drove an additional 18.4% loss on top of the lifestyle effect. SURMOUNT-4 demonstrated that stopping tirzepatide leads to substantial regain — about 14% of body weight came back over 52 weeks — confirming what most clinicians now treat as obvious: tirzepatide is for chronic, ongoing use, not a 6-month fix.

04 Tirzepatide vs semaglutide (and everything else)

Tirzepatide is most often compared to semaglutide — the active ingredient in Ozempic and Wegovy. Both are GLP-1 receptor agonists; only tirzepatide adds GIP. The pivotal head-to-head trial was SURPASS-2 (in patients with type 2 diabetes), which showed tirzepatide produced about 1.5–2× more weight loss across all dose pairs.

Quick comparison snapshot

For a deeper dive — including the dose-conversion calculator, side-effect comparison, and switch protocol — see our full tirzepatide vs semaglutide guide. We also have shorter explainers on tirzepatide vs Ozempic and Wegovy and tirzepatide vs retatrutide, the next-generation triple agonist now in late-stage trials.

05 Dosing & titration at a glance

Tirzepatide dosing is identical for Mounjaro, Zepbound, and most legitimate compounding pharmacies. You start at 2.5 mg once weekly and increase the dose every 4 weeks until you reach a maintenance dose that controls appetite without intolerable side effects.

Most patients land on a maintenance dose between 5 mg and 12.5 mg, depending on response and tolerance. Going to the max isn't required and isn't always better — appetite suppression can plateau, and side effects climb non-linearly above 10 mg. Our full dosing guide includes the unit-conversion calculator, vial reconstitution math, and a printable titration timeline.

06 Side effects you should actually expect

About 80% of side effects are gastrointestinal: nausea, diarrhea, constipation, vomiting, indigestion, and burping. Most are mild to moderate, peak in the first 1–2 weeks after each dose increase, and fade as your body adapts. They are not a sign the drug is "wrong" — they're predictable.

Common (≥5% of patients in trials)

• Nausea — 28% (peaks during titration; eat smaller, blander meals)
• Diarrhea — 21% (often early; usually self-limited)
• Constipation — 17% (manage with water + fiber)
• Vomiting — 13% (more common at higher doses)
• Decreased appetite — 11% (this is the point, not a side effect)
• Fatigue — 7% (resolves for most after the first month)
• Injection-site reactions — 5% (mild redness, fades in 24–48h)

Less common but serious

• Pancreatitis — rare; severe abdominal pain that radiates to the back warrants ER evaluation.
• Gallbladder problems — gallstones and cholecystitis happen at modestly higher rates than placebo.
• Hypoglycemia — only relevant if you also take insulin or sulfonylureas.
• Thyroid C-cell tumors — boxed warning based on rodent studies; no proven human risk. Contraindicated if personal/family history of MTC or MEN 2.
• Diabetic retinopathy worsening — for diabetics with pre-existing retinopathy.

For the full breakdown — including how to manage GI symptoms day-to-day, hair loss data, alcohol interactions, and the truth about long-term effects — see our tirzepatide side effects guide.

07 What does tirzepatide cost?

Tirzepatide pricing in 2026 sits in three tiers, separated by an order of magnitude:

Insurance complicates the picture: Zepbound is covered by some commercial plans (with prior authorization) but rarely by Medicare or Medicaid as of 2026. Coverage and copays vary so widely that the simplest path for most cash patients is to skip insurance entirely and use a telehealth provider with transparent monthly pricing. We rank providers by real out-of-pocket cost in our cost comparison and how-to-get-online guide.

08 Other approved uses

Beyond weight management, tirzepatide is FDA-approved for two other conditions:

• Type 2 diabetes (Mounjaro, since 2022) — produces an average HbA1c reduction of 1.8–2.4 percentage points, often greater than dual oral therapy.
• Obstructive sleep apnea (Zepbound, since December 2024) — the SURMOUNT-OSA trial showed a 51-event/hour drop in apnea-hypopnea index for moderate-to-severe OSA in adults with obesity. This is the first medication ever approved for OSA.

Active research is also looking at tirzepatide in heart failure with preserved ejection fraction (HFpEF — already showed benefit in SUMMIT trial), MASLD/MASH (fatty liver), chronic kidney disease in T2D, and potentially Alzheimer's prevention. None of those are currently approved indications, but the breadth of trials reflects how transformative the dual-agonist mechanism has turned out to be.

09 How to actually get tirzepatide

There are three legitimate routes in 2026:

1. Insurance through your primary doctor. Zepbound has commercial coverage with prior authorization in many large employer plans. If you qualify (BMI ≥30, or ≥27 with a comorbidity), this can be the cheapest option — sometimes $25/month with a copay card. Downside: 4–8 weeks of prior auth back-and-forth, and many plans now exclude weight-loss drugs entirely.
2. Lilly Direct vials (self-pay). Eli Lilly's own direct-to-consumer program ships single-dose vials to your door for $349 (2.5 mg) or $499 (5/7.5/10/12.5/15 mg) per month. You still need a prescription, but Lilly will connect you to a telehealth provider if you don't have one.
3. Telehealth + compounded tirzepatide. The fastest, cheapest, and most popular cash route. A 10-minute online consult with a US-licensed provider, no insurance, and monthly delivery from a state-licensed compounding pharmacy. Prices start at $199/month. Quality varies by provider — see our provider reviews for an independent ranking.

The full walkthrough — including which providers ship to your state, what to expect during the consult, and how to spot red flags — is in our how to get tirzepatide online guide.

10 Smart-shopper FAQ

Where to go next

This guide is the entry point. Below are the deep dives — each is a standalone hub for the topic.