Tirzepatide is a dual-agonist peptide: it activates receptors for two gut hormones at once — GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). It is sold as Mounjaro (approved for type 2 diabetes) and Zepbound (approved for chronic weight management and, more recently, obstructive sleep apnea in adults with obesity), both once-weekly injections.

In plain English: like semaglutide, tirzepatide mimics the body's post-meal signaling — boosting insulin release when glucose is high, slowing stomach emptying, and dialing down appetite in the brain. The addition of GIP activity is the differentiator. GIP is the other major incretin hormone, and the dual action appears to amplify both the glycemic and the weight effects; in head-to-head diabetes trials, tirzepatide produced larger HbA1c and weight reductions than semaglutide 1 mg. Researchers are still working out exactly how much the GIP component contributes mechanistically.

Regulatory status: tirzepatide is an FDA-approved prescription drug — Mounjaro in 2022, Zepbound in 2023 — and is approved by the EMA and other major regulators. As with semaglutide, compounded or gray-market "tirzepatide" is not the approved product: after the official shortage ended, the FDA moved to curtail mass compounding, and it has warned about safety risks including dosing errors with compounded versions.

Tirzepatide's evidence base comes from two large randomized controlled trial programs:

• SURPASS (type 2 diabetes): across the program, tirzepatide produced HbA1c reductions around 2 percentage points or more, and in SURPASS-2 it outperformed semaglutide 1 mg on both glucose control and weight;
• SURMOUNT (weight management): in SURMOUNT-1, adults with obesity lost an average of roughly 15% of body weight on 5 mg, 19.5% on 10 mg, and 20.9% on 15 mg over 72 weeks, versus about 3% with placebo — among the largest reductions recorded for any medication in a randomized trial;
• SURMOUNT-OSA: reductions in sleep-apnea severity in adults with obesity, supporting the 2024 approval for that indication. A cardiovascular outcomes trial (SURPASS-CVOT) has since reported tirzepatide non-inferior to dulaglutide on major cardiovascular events.

As with semaglutide, these are placebo-controlled trials with thousands of participants, so both benefits and harms are quantified rather than anecdotal.

Why the dual mechanism appears to matter is still an active research question. GIP on its own was long considered a disappointing drug target — its effects on insulin release weaken in type 2 diabetes — yet pairing it with GLP-1 agonism produced results that beat GLP-1 alone in head-to-head testing. Competing explanations include GIP's actions in fat tissue and the brain, and possible receptor-level interactions. For a lay reader the takeaway is simpler: the combination has stronger average trial results, and the mechanism story behind that edge is not fully settled.

The same honest caveats apply: stopping the drug tends to reverse the effect (in SURMOUNT-4, participants switched to placebo regained much of the weight within a year while those continuing lost more), and part of the loss is lean mass — which is why trial protocols pair the drug with diet and activity counseling.

Tirzepatide's side-effect profile closely mirrors the GLP-1 class, led by gastrointestinal effects during escalation:

• Very common: nausea, diarrhea, vomiting, constipation, decreased appetite, abdominal pain — most prominent as doses step up, typically moderating over time;
• Gallbladder events and pancreatitis: reported at higher rates than placebo, as with other incretin drugs;
• Boxed warning: thyroid C-cell tumors in rodent studies; contraindicated with a personal or family history of medullary thyroid carcinoma or MEN 2 syndrome;
• Hypoglycemia when combined with insulin or sulfonylureas; dehydration-related kidney injury from severe GI losses; delayed stomach emptying relevant before anesthesia;
• Counterfeit and compounding risk: with demand outstripping supply at times, counterfeit pens and unregulated "tirzepatide" vials have circulated; compounded products are not FDA-reviewed and have generated dosing-error reports.

These risks are the reason the approved products exist inside a prescription relationship with screening and monitoring rather than as over-the-counter products.

Tirzepatide dosing is defined by its FDA prescribing information, again built around gradual escalation for tolerability. As described there:

• Treatment is described as starting at 2.5 mg once weekly for four weeks — a dose intended for initiation, not glycemic control or weight efficacy;
• The label describes increasing in 2.5 mg increments no more often than every four weeks, through 5, 7.5, 10, and 12.5 mg, to a maximum of 15 mg once weekly;
• Maintenance doses studied in trials were 5, 10, and 15 mg weekly; prescribing information describes selecting among them based on response and tolerability.

The four-week spacing between steps reflects the drug's five-day half-life — each dose level needs about a month to reach its steady-state plateau before tolerability and response can be judged fairly. Prescribing information also addresses missed doses: it describes taking a missed dose within four days, and otherwise skipping to the next scheduled one — a rule that only makes sense because so much drug remains on board between weekly injections. These figures summarize the approved labeling; individual prescriptions are a clinician's decision, and nothing here is a recommendation.

Tirzepatide's elimination half-life is about 120 hours — roughly five days — which places it, like semaglutide, firmly in once-weekly territory. The molecule's albumin binding slows its clearance enough that levels remain substantial across the full week between injections.

The practical consequences of a five-day half-life: levels accumulate over the first several weeks of consistent dosing before flattening at steady state (around four weeks), a missed dose leaves meaningful drug on board for days rather than hours, and full washout after a final dose takes several weeks. Prescribing information's four-week escalation intervals map directly onto this accumulation curve.

It is worth pausing on what "steady state" means, because it is the least intuitive part of long-half-life pharmacology. During the first weeks of dosing, each injection adds more than the body clears, so the average level climbs even though the dose hasn't changed. At steady state the two finally balance — which is why side effects can build for weeks on a constant dose, and why judging a dose level after one injection misreads the drug.

For anyone tracking a weekly compound, the useful discipline is a consistent injection day and a complete log of dose changes — the level in the body at any moment is a function of the past month of entries.