Tirzepatide: What It Is, Where to Get It Prescribed, and What It Costs

Tirzepatide is a 39-amino-acid synthetic peptide built on the backbone of GIP, glucose-dependent insulinotropic polypeptide, one of the two gut hormones released after a meal. It is engineered to activate both the GIP receptor and the GLP-1 receptor, which is why the literature calls it a dual GIP/GLP-1 receptor agonist. A fatty-acid side chain lets it bind albumin in the blood, stretching its half-life to about five days and allowing once-weekly injection.

The "dual" part is the reason the compound exists. Semaglutide and the older GLP-1 medications act on one receptor; tirzepatide was built to test whether adding the GIP arm produced more, and the head-to-head trials below answer that question.

Tirzepatide was developed by Eli Lilly under the code LY3298176. The FDA approved it as Mounjaro for type 2 diabetes in May 2022 and as Zepbound for chronic weight management in November 2023; in December 2024 Zepbound also received approval for moderate-to-severe obstructive sleep apnoea in adults with obesity. Mounjaro and Zepbound are the same molecule at the same doses under two names.

What Pepti supplies is compounded tirzepatide: the same active ingredient, prepared by a state-licensed pharmacy to an individual prescription, combined with cyanocobalamin (vitamin B12) in a multi-dose vial. It is not Mounjaro or Zepbound and is not FDA approved as a finished product. That distinction runs through this page, because the trial evidence belongs to the branded product.

It is not a stimulant or a thermogenic and it does not force the body to burn anything. It is a hormone-receptor agonist that changes signalling around food intake and insulin; the weight change reported in trials follows from people eating less over a long period. It is also not a short course: the trials ran 40 to 72 weeks, and weight tends to return when the medication stops.

GLP-1 is released from the gut after eating. Activating its receptor increases insulin release when glucose is high, suppresses glucagon, slows gastric emptying, and acts on appetite centres in the brainstem and hypothalamus to reduce hunger and increase fullness. These effects are well characterised in humans from two decades of GLP-1 medication research. The slowing of gastric emptying, strongest in the early weeks before the body adapts, is also behind two practical points covered later: gastrointestinal side effects that cluster around dose increases, and reduced absorption of oral contraceptives after starting or stepping up.

GIP is the other incretin. On its own it has a modest insulin-releasing effect in type 2 diabetes and was long considered a dead end for drug development. GIP receptors sit on fat cells and in the brain as well as the pancreas, and the proposed contributions of the GIP arm include effects on insulin sensitivity, on how adipose tissue handles fat, and possibly on nausea tolerance. Some of that remains hypothesis; the clinical result is not.

A 2022 phase 1 study in The Lancet Diabetes & Endocrinology measured islet function and insulin sensitivity directly, with clamp techniques, in adults with type 2 diabetes randomised to tirzepatide 15 mg, semaglutide 1 mg or placebo for 28 weeks. It reported that tirzepatide improved the clamp disposition index, a combined measure of insulin secretion and sensitivity, with gains in insulin sensitivity larger than the weight change alone would predict. That is direct human evidence that the compound acts on glucose handling through more than one route.

SURMOUNT-1, in the New England Journal of Medicine in 2022, randomised 2,539 adults with obesity, or overweight plus a weight-related complication, to tirzepatide 5, 10 or 15 mg weekly or placebo for 72 weeks. Mean weight change was −15.0 percent at 5 mg, −19.5 percent at 10 mg and −20.9 percent at 15 mg, against −3.1 percent with placebo. Between 85 and 91 percent of participants on tirzepatide lost at least 5 percent of body weight, compared with 35 percent on placebo, and 57 percent of the 15 mg group lost 20 percent or more.

SURMOUNT-5, in the New England Journal of Medicine in 2025, is the head-to-head trial. It randomised 751 adults with obesity and no diabetes to the maximum tolerated dose of tirzepatide (10 or 15 mg) or semaglutide (1.7 or 2.4 mg) for 72 weeks. Mean weight change was −20.2 percent with tirzepatide and −13.7 percent with semaglutide; waist circumference fell 18.4 cm and 13.0 cm. Participants on tirzepatide were more likely to reach every threshold from 10 to 25 percent. The trial was open-label, so participants knew which drug they were on, which is a real limitation.

SURMOUNT-2, in The Lancet in 2023, randomised 938 adults with obesity and type 2 diabetes to tirzepatide 10 mg, 15 mg or placebo for 72 weeks. Weight change was −12.8 and −14.7 percent against −3.2 percent with placebo. The smaller effect than in SURMOUNT-1 is consistent across the class: people with type 2 diabetes generally lose less on these medications than people without it.

SURPASS-2, in the New England Journal of Medicine in 2021, compared tirzepatide 5, 10 and 15 mg with semaglutide 1 mg in 1,879 people with type 2 diabetes over 40 weeks. HbA1c fell 2.01, 2.24 and 2.30 percentage points against 1.86 with semaglutide, and tirzepatide was non-inferior and superior at every dose. Weight reductions were also larger with tirzepatide, by 1.9 to 5.5 kg. The comparator was the 1 mg diabetes dose, not the 2.4 mg weight-management dose, so this is not a weight-loss head-to-head; SURMOUNT-5 is.

SURMOUNT-OSA, in the New England Journal of Medicine in 2024, ran two 52-week trials in adults with moderate-to-severe obstructive sleep apnoea and obesity, one in people not using positive airway pressure and one in people already using it. The apnoea-hypopnoea index fell 25.3 and 29.3 events per hour with tirzepatide against 5.3 and 5.5 with placebo. This is the trial behind the December 2024 Zepbound approval for sleep apnoea.

SURPASS-CVOT, in the New England Journal of Medicine in December 2025, randomised 13,299 people with type 2 diabetes and established cardiovascular disease to tirzepatide or dulaglutide, an older GLP-1 medication already shown to reduce cardiovascular events, with a median follow-up of about four years. The composite of cardiovascular death, heart attack or stroke occurred in 12.2 percent on tirzepatide and 13.1 percent on dulaglutide. Tirzepatide met non-inferiority; the difference did not reach significance for superiority. The honest reading is that tirzepatide is at least as safe as an established cardioprotective comparator on hard outcomes, not that it has been shown to be better.

A great deal. The SURPASS and SURMOUNT programmes enrolled tens of thousands of participants in randomised, mostly double-blind, placebo- or active-controlled trials of 40 to 72 weeks, with a four-year cardiovascular outcomes trial on top. This is the standard of evidence behind any approved medication, and it is why tirzepatide is FDA approved under two brand names.

What it does not directly cover is the compounded preparation. The trials used the manufacturer's pens. A compounded vial contains the same active ingredient at the same weekly doses but has not itself been through a trial, and no compounded medication has. The pharmacology is what the trials describe; the quality of any given vial depends on the pharmacy that made it, which is what Pepti's quality standards cover.

• It does not establish that the compounded preparation performs identically to the branded pen. That has not been trialled and is not claimed.
• It does not establish what happens after stopping, other than that regain is common. SURMOUNT-4, a withdrawal trial, reported substantial regain over a year after switching to placebo.
• It does not establish safety in pregnancy, under 18, or with a personal or family history of medullary thyroid carcinoma, all excluded from the trials.
• It does not establish a benefit outside the weight range the trials enrolled: BMI 30 or more, or 27 or more with a complication. It is not a tool for the last few pounds, and a physician will not prescribe it that way.

Mounjaro (type 2 diabetes) and Zepbound (chronic weight management; obstructive sleep apnoea with obesity) are FDA-approved tirzepatide products made by Eli Lilly. Both carry a boxed warning about thyroid C-cell tumours seen in rodents, and both are contraindicated with a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2.

From late 2022 the FDA listed tirzepatide as in shortage. Under federal compounding law a drug on the shortage list may be compounded even though it is essentially a copy of an approved product, and that is what allowed compounded tirzepatide to be dispensed at scale through 2023 and 2024.

The FDA declared the shortage resolved on 2 October 2024, was sued by the Outsourcing Facilities Association, agreed to reconsider, and reaffirmed its decision on 19 December 2024. That decision set two wind-down periods: 503A pharmacies until 18 February 2025 and 503B outsourcing facilities until 19 March 2025, after which normal enforcement applies. In March 2025 a federal district court in Texas declined to block the decision, finding the agency had acted within its authority.

Tirzepatide is no longer in shortage, so the shortage exemption no longer applies. The FDA's guidance page for compounders, last updated 1 April 2026, sets out the rules that govern it now. A compounded drug is "essentially a copy" of an approved product if it contains the same active ingredient in the same, similar or easily substitutable strength by the same route. A 503A pharmacy may still compound such a product when a prescriber determines and documents that a change in it produces a significant difference for an identified individual patient. The FDA has said that adding vitamin B12 does not by itself take a product outside that definition where the amounts are within 10 percent of commercially available strengths.

On 30 April 2026 the FDA proposed to exclude semaglutide, tirzepatide and liraglutide from the 503B bulks list, stating it did not identify a clinical need for outsourcing facilities to compound them from bulk substances. The comment period was extended to 30 July 2026 and no final determination has been published as of this writing. That proposal concerns 503B facilities, which compound in bulk without patient-specific prescriptions; it does not change the 503A framework above.

So the accurate description today is: an FDA-approved molecule; a compounded version that is not an approved product and is no longer covered by a shortage exemption; prescribable through a state-licensed 503A pharmacy where the physician documents a patient-specific reason for the compounded formulation; and a proposed, not final, closure of the separate 503B bulk route.

The branded label starts everyone at 2.5 mg weekly for four weeks, described as a tolerance phase rather than a treatment dose. Appetite change is usually noticed within the first one or two injections; weight change in the first month is modest. Nausea, if it comes, tends to arrive in the two or three days after an injection and to ease as the weeks pass.

Dose is increased in steps, at intervals of at least four weeks, toward whichever maintenance dose the physician chooses. This is where most of the weight change in the trials happened: SURMOUNT-1's dose-escalation period ran twenty weeks and its weight curves are steepest here. Side effects cluster around each step up.

Weight change in the trials continued past a year and was still flattening at 72 weeks. Prescribers generally describe a plateau somewhere between months nine and fifteen, at which point the conversation becomes maintenance dose rather than further escalation. Bloodwork is usually repeated in this window.

There is no withdrawal syndrome. Appetite returns over a few weeks as the drug clears, and the SURMOUNT withdrawal trial reported substantial regain over the following year in people switched to placebo. That is why treatment is framed as ongoing rather than as a course, and why refills run on 28-day fills.

The six vials are dose-specific: each is concentrated so that 0.50 mL delivers the weekly dose on the label. That is 50 units on a U-100 insulin syringe at every strength from 2.5 mg to 15 mg. When your dose changes, the pharmacy changes the concentration and you keep drawing to the same line. Drawing errors are the most common problem the FDA has reported with compounded incretin medications, and a fixed volume removes most of the arithmetic.

Subcutaneous means into the fat layer, not the muscle. Abdomen, thigh and upper arm are the usual sites, rotated. Pick a day of the week and keep it; the branded label allows the day to move as long as at least three days separate doses. Your physician's directions cover a missed dose.

A 2 mL vial at 0.50 mL per dose is four doses, which at once weekly is four weeks. That is why refills run on a 28-day cycle and why the strength tiers map one-to-one onto the dose steps. One vial per fill, always; a change in dose is a change in which vial you are sent, not in how much you draw.

Refrigerated, and it ships that way in insulated packaging with ice packs. Beyond-use dating runs from first puncture and is on the label. Keep it in the refrigerator between weekly doses; do not freeze it.

Nausea, diarrhoea, vomiting, constipation and reduced appetite are the most common adverse events in every tirzepatide trial. Most are mild to moderate, occur during dose escalation, and settle. In SURMOUNT-1, adverse events led to discontinuation in 4.3 to 7.1 percent on tirzepatide against 2.6 percent on placebo; in SURPASS-2, nausea was reported by 17 to 22 percent on tirzepatide and 18 percent on semaglutide. Injection-site reactions, hair thinning during rapid weight loss, and fatigue are also reported.

Tirzepatide caused thyroid C-cell tumours in rats at clinically relevant exposures. Whether it does so in humans is unknown, and the branded label carries a boxed warning on that basis, which is why personal or family history of medullary thyroid carcinoma or MEN 2 is a contraindication rather than a discussion point. Acute pancreatitis has been reported with incretin medications, and gallbladder events, including gallstones, occur more often with rapid weight loss on any treatment. Severe, persistent abdominal pain is the reason to stop and contact your physician.

On its own tirzepatide rarely causes low blood glucose (under 2 percent in SURPASS-2), but the risk rises with insulin or a sulfonylurea, one reason a full medication list is part of the intake. Because gastric emptying slows, oral contraceptives may be absorbed less reliably for four weeks after starting and after each dose increase; the branded label advises a backup or non-oral method during those windows.

Stop and contact your physician for any reaction that is severe, spreading, involves difficulty breathing, or involves changes in vision.

Same class, different receptor coverage. Semaglutide acts on the GLP-1 receptor only; tirzepatide acts on GLP-1 and GIP. In SURMOUNT-5 tirzepatide produced −20.2 percent against −13.7 percent for semaglutide over 72 weeks, and in SURPASS-2 it lowered HbA1c more than semaglutide 1 mg. Semaglutide has a longer track record, a cardiovascular outcomes trial in obesity that tirzepatide does not yet have, and a lower price; gastrointestinal side effects are broadly similar. Which one a physician prescribes depends on history, goals, tolerance and cost, and starting on one does not rule out the other.

Same molecule, same weekly doses, different product. The branded pens are FDA-approved and are what every trial on this page used. Compounded tirzepatide is prepared by a state-licensed pharmacy to an individual prescription, combined here with cyanocobalamin, in a multi-dose vial drawn with a syringe; it is not FDA approved and no trial has been run on it. The identity, purity and sterility of the vial rest on the pharmacy, which is why Pepti uses FDA-registered pharmacies. If your insurance covers the branded product, that is worth discussing with your physician.

Tirzepatide is not offered as a pepti Pen cartridge. It is supplied as a vial drawn with an insulin syringe, and because every strength is dosed at the same 0.50 mL, the draw is the same at every step.