Tirzepatide: Dosing, Weight Loss Results & FDA Approval

What is tirzepatide approved for?

Tirzepatide activates both the GIP receptor and the GLP-1 receptor, and its labels describe it as a dual agonist rather than a pure GLP-1 drug [1]. It is marketed as two products with different approved uses.

Zepbound (NDA 217806, approved 8 November 2023) is indicated, with a reduced-calorie diet and more physical activity, to reduce excess body weight and maintain weight reduction long term in adults with obesity, or adults with overweight plus at least one weight-related comorbid condition. It is also indicated to treat moderate to severe obstructive sleep apnea in adults with obesity, an indication added on 20 December 2024 [1]. The Zepbound label lists no pediatric indication and states that safety and effectiveness in pediatric patients are not established [1].

Mounjaro (NDA 215866, approved 13 May 2022) is indicated as an adjunct to diet and exercise to improve glycemic control in adults and in children 10 years and older with type 2 diabetes, and to reduce the risk of major adverse cardiovascular events in adults with type 2 diabetes at high risk for them [2]. Mounjaro is not labeled for weight loss [2].

The Zepbound label says not to coadminister it with another tirzepatide-containing product or with any GLP-1 receptor agonist [1].

How is tirzepatide dosed?

The Zepbound label starts treatment at 2.5 mg injected subcutaneously once weekly for 4 weeks. That dose is for treatment initiation and is not approved as a maintenance dose. After 4 weeks the label moves to 5 mg once weekly, and allows increases in 2.5 mg increments after at least 4 weeks on the current dose [1]. The label adds that if a maintenance dose is not tolerated, a lower one can be considered [1].

Zepbound maintenance doses are 5 mg, 10 mg or 15 mg once weekly for weight reduction, and 10 mg or 15 mg for obstructive sleep apnea. The maximum is 15 mg weekly [1]. The Mounjaro label starts at 2.5 mg weekly and raises the dose in 2.5 mg steps after at least 4 weeks if more glycemic control is needed; the maximum is 15 mg weekly in adults and 10 mg weekly in children 10 years and older [2].

The Zepbound label says it can be administered at any time of day, with or without food, in the abdomen, thigh, or back of the upper arm, with the injection site rotated. After a missed dose, the label allows administration within 4 days (96 hours); after that, the missed dose is skipped and the regular schedule is resumed. The weekly day can be changed as long as doses are at least 3 days (72 hours) apart. The label lists presentations as a vial, a prefilled single-dose pen, and a single-patient-use KwikPen, and states no dose adjustment is needed for renal or hepatic impairment [1].

How much weight loss does tirzepatide produce?

In SURMOUNT-1, 2,539 adults with obesity, or overweight plus a weight-related complication, and without diabetes, received tirzepatide 5 mg, 10 mg or 15 mg or placebo for 72 weeks. Mean weight change was -15.0% on 5 mg, -19.5% on 10 mg and -20.9% on 15 mg, against -3.1% on placebo [3]. Weight loss of at least 5% occurred in 85%, 89% and 91% versus 35% on placebo, and loss of at least 20% occurred in 30.0%, 50.1% and 56.7% versus 3.1% [1][3].

SURMOUNT-2 tested the same drug in 938 adults with type 2 diabetes and a BMI of 27 or higher. Weight change at 72 weeks was -12.8% on 10 mg and -14.7% on 15 mg, against -3.2% on placebo; at least 5% weight loss occurred in 79.2% and 82.8% versus 32.5% [4].

SURMOUNT-3 enrolled 579 adults who had already lost at least 5% of body weight during a 12-week intensive lifestyle program. Over the next 72 weeks they lost an additional 18.4% on tirzepatide and gained 2.5% on placebo [5].

In obstructive sleep apnea, two 52-week trials measured the apnea-hypopnea index. It fell by 25.3 events per hour versus 5.3 on placebo in the trial without positive airway pressure therapy, and by 29.3 versus 5.5 events per hour in the trial where participants used it [6].

A body-composition substudy of 160 SURMOUNT-1 participants who had DXA scans found fat mass fell 33.9% and lean mass 10.9% with tirzepatide, against 8.2% and 2.6% with placebo. About 75% of the weight lost was fat mass and about 25% lean mass, the same split seen with placebo [7].

Tirzepatide compared with semaglutide

SURMOUNT-5 was an open-label head-to-head trial of 751 adults with obesity but no diabetes, comparing the maximum tolerated dose of tirzepatide (10 or 15 mg) with the maximum tolerated dose of semaglutide (1.7 or 2.4 mg) over 72 weeks. Weight fell 20.2% with tirzepatide and 13.7% with semaglutide, and waist circumference fell 18.4 cm versus 13.0 cm [8].

In type 2 diabetes, SURPASS-2 randomized 1,879 adults to tirzepatide 5, 10 or 15 mg or semaglutide 1 mg for 40 weeks. HbA1c fell 2.01, 2.24 and 2.30 points versus 1.86, and weight fell 7.6, 9.3 and 11.2 kg versus 5.7 kg [9]. Whether the added GIP activity explains the difference between the two drugs is not established by these trials [9][8].

What happens when tirzepatide is stopped?

SURMOUNT-4 enrolled 783 adults for a 36-week open-label run-in, and 670 of them were then randomized to continue tirzepatide or switch to placebo for 52 weeks. The 670 who were randomized had lost a mean 20.9% of body weight during the run-in. From week 36 to week 88, weight changed by -5.5% in people who continued and +14.0% in those switched to placebo, a difference of 19.4 percentage points [10].

Side effects

In the pooled Zepbound weight-management trials (placebo 958 people; 5 mg 630; 10 mg 948; 15 mg 941; up to 72 weeks), the label reports nausea in 8% on placebo versus 25%, 29% and 28% on the three doses; diarrhea 8% versus 19%, 21% and 23%; vomiting 2% versus 8%, 11% and 13%; constipation 5% versus 17%, 14% and 11%; abdominal pain 5% versus 9%, 9% and 10%; and dyspepsia 4% versus 9%, 9% and 10% [1]. Any gastrointestinal adverse reaction occurred in 56% on every tirzepatide dose versus 30% on placebo. Treatment was stopped for an adverse reaction by 4.8%, 6.3% and 6.7% on the three doses versus 3.4% on placebo, and for gastrointestinal reasons by 1.9%, 3.3% and 4.3% versus 0.5% [1]. Most nausea, vomiting and diarrhea occurred during dose escalation and decreased over time [1].

Hair loss was reported by 1% on placebo versus 5%, 4% and 5% on the three doses; the label ties it to weight reduction and reports it in 7.1% of women versus 0.5% of men on Zepbound [1]. Mean resting heart rate rose 1 to 3 beats per minute, and hypotension was reported in 1.6% versus 0.1% on placebo [1].

The Mounjaro label reports its own rates from type 2 diabetes trials, where nausea occurred in 4% on placebo versus 12%, 15% and 18% on 5, 10 and 15 mg; the label notes that rates from different trials are not directly comparable [2].

Boxed warning, contraindications and label warnings

Both labels carry a boxed warning for thyroid C-cell tumors. In rats, tirzepatide caused dose- and duration-dependent thyroid C-cell tumors at clinically relevant exposures; whether it causes them in humans, including medullary thyroid carcinoma, is unknown [1]. Tirzepatide is contraindicated in people with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2, and in people with a known serious hypersensitivity to tirzepatide or an excipient [1]. The label calls routine calcitonin monitoring or thyroid ultrasound of uncertain value for early detection [1].

Other Zepbound warnings cover severe gastrointestinal reactions (the drug is not recommended in severe gastroparesis; severe GI reactions occurred in 1.7%, 2.5% and 3.1% versus 1% on placebo), acute kidney injury from volume depletion, acute gallbladder disease (cholecystitis 0.7% versus 0.2%; cholelithiasis 1.1% versus 1%), acute pancreatitis (stop if suspected), serious hypersensitivity, hypoglycemia, diabetic retinopathy complications, and pulmonary aspiration during general anesthesia or deep sedation [1]. Hypoglycemia is more frequent with insulin or a sulfonylurea; in SURMOUNT-2, glucose below 54 mg/dL occurred in 10.3% of those on a sulfonylurea versus 2.1% of those not on one [1].

For pregnancy, the Zepbound label states that weight loss offers no benefit in pregnancy and may cause fetal harm, and that the drug should be discontinued when pregnancy is recognized [1]. In a single-dose study of 11 lactating women, tirzepatide was undetectable or very low in breast milk, with no data on the infant or on milk production [1].

Tirzepatide delays gastric emptying, so it can change how oral drugs are absorbed. The label advises people using oral hormonal contraceptives to switch to a non-oral method or add a barrier method for 4 weeks after starting and for 4 weeks after each dose escalation; non-oral hormonal methods should not be affected [1]. In a drug-interaction study with a single 5 mg dose, peak levels of ethinyl estradiol, norgestimate and norelgestromin fell 59%, 66% and 55%, while total exposure fell 20% to 23% [1]. For other oral drugs, the label advises monitoring those that depend on threshold concentrations or have a narrow therapeutic index, such as warfarin; acetaminophen peak concentration fell 55% after a first 5 mg dose, and by week 6 on 15 mg there was no meaningful effect [1].

Is compounded tirzepatide FDA-approved?

No. FDA declared the tirzepatide injection shortage resolved on 19 December 2024, and the transition periods for compounders ended after a court denied a preliminary injunction on 5 March 2025 for state-licensed pharmacies and on 19 March 2025 for outsourcing facilities [11]. Since then, a compounded product that is essentially a copy of the approved drug is allowed only if it is not made regularly or in inordinate amounts (FDA says it does not intend to act against four or fewer such prescriptions per month), or if the prescriber documents a significant difference for an identified patient [11].

FDA states that compounded drugs are not FDA approved and are not reviewed for safety, effectiveness or quality before marketing, and that as of 31 May 2026 it had received more than 730 adverse event reports for compounded tirzepatide, which it says likely undercount [12]. On 30 April 2026 FDA proposed to exclude tirzepatide from the list of bulk substances that outsourcing facilities may compound with, finding no clinical need; comments ran to 29 June 2026, and FDA said no final decision had been made [13].