Tirzepatide dosage: the labeled schedule, the trial protocols, and the PK record.

> the short version

Tirzepatide is given as a once-weekly subcutaneous injection (under the skin). The FDA-labeled starting dose is 2.5 mg per week. The dose is increased in steps every four weeks to reach a maintenance dose — the prescribing information labels 5, 10, and 15 mg as maintenance options, with 15 mg as the maximum. Most people start at the lowest dose to minimize side effects during the body's adjustment period.

The drug stays in the body for about five days after each dose (its half-life — the time for concentration to fall by half). That long duration is what makes once-weekly dosing work: the level in the blood stays relatively stable between injections.

All dose figures on this page are drawn from the FDA prescribing label ^[5] and the published phase 3 trial protocols ^{[1] [2]} — they document what was studied and approved, not a personal recommendation.

Tirzepatide dosage: the FDA-labeled titration

The FDA prescribing information for tirzepatide (for the type 2 diabetes indication, approved May 2022) documents the following subcutaneous dose schedule ^[5]:

• Starting dose: 2.5 mg once weekly for 4 weeks
• Dose escalation: increase by 2.5 mg every 4 weeks as tolerated
• Maintenance doses studied: 5 mg, 10 mg, 15 mg once weekly
• Maximum labeled dose: 15 mg once weekly

The stepwise titration is designed to minimize gastrointestinal adverse events, which are most intense during dose escalation. The 4-week interval at each level allows GI tolerance to develop. Not all patients tolerate the maximum dose; the label and trial protocols allow dosing at the maximum tolerated dose ^[1].

The labeled obesity indication (approved November 2023) follows the same titration pattern as the type 2 diabetes label ^[31].

Tirzepatide dose in clinical trials

Across the phase 3 programme, three maintenance doses were evaluated:

5 mg once weekly: The lowest maintenance dose. SURMOUNT-1 measured -15.0% body weight at 72 weeks in people with obesity versus -3.1% placebo ^[1]. SURPASS-2 measured HbA1c reduction of -2.01 pp versus -1.86 pp with a selective GLP-1 agonist at 40 weeks ^[2].

10 mg once weekly: SURMOUNT-1 measured -19.5% body weight at 72 weeks ^[1]. SURPASS-2 measured HbA1c -2.24 pp ^[2].

15 mg once weekly (maximum): SURMOUNT-1 measured -20.9% body weight at 72 weeks ^[1]. SURPASS-2 measured HbA1c -2.30 pp ^[2]. SURMOUNT-5 used 10 or 15 mg (maximum tolerated dose) and measured -20.2% body weight versus -13.7% with a selective GLP-1 agonist over 72 weeks ^[3].

Phase 1 dose-ranging in 142 human subjects confirmed pharmacokinetics supporting once-weekly dosing and showed reduced fasting glucose and body weight versus placebo at sub-therapeutic doses ^[7].

Half-life and pharmacokinetics

Elimination half-life: approximately 5 days. This is the consequence of the fatty-diacid (C20 eicosanedioic acid) modification attached via a glutamic acid linker and two AEEA spacer units to the peptide backbone. This arm binds tightly to serum albumin (the most abundant protein in plasma), which dramatically slows renal filtration and proteolytic clearance ^[7].

Route: subcutaneous injection only. No intravenous, intramuscular, or oral formulation has been studied in the phase 3 programme. The injection is administered once weekly at approximately the same time each week, on any day of the week.

Gastric emptying effect: tirzepatide transiently delays gastric emptying (the rate at which the stomach passes food to the small intestine) to a degree comparable to selective long-acting GLP-1 receptor agonists. This effect attenuates with continued dosing ^[24]. The delay is the mechanism for both the appetite-reduction benefit and the GI side-effect profile, and it is also why perioperative aspiration risk is a recognized caution ^[25].

Body weight changes are driven primarily by reduced appetite and food intake rather than by GI adverse events. A post-hoc analysis from the SURPASS programme found that weight reduction occurred independently of whether gastrointestinal events were experienced ^[9].

Tirzepatide injection sites and administration

Tirzepatide injection is given subcutaneously. Approved sites: abdomen, thigh, or upper arm. The site may be rotated with each injection to reduce injection-site reactions (redness, tenderness, bruising), which are the second most commonly reported category in post-market safety data.

Storage: marketed formulations are refrigerated. Specific reconstitution and storage parameters are formulation-dependent and documented in the prescribing information — outside the scope of the published efficacy literature. The prescribing information is the authoritative source for storage requirements ^[5].