Tirzepatide dosage: labeled dose ranges, titration schedule, and the pharmacokinetics behind once-weekly administration.

The short version

Tirzepatide is given as a subcutaneous (under the skin) injection once a week. The FDA-labeled starting dose is 2.5 mg once weekly; the dose is increased every 4 weeks as tolerated up to a maximum of 15 mg once weekly. This slow titration schedule is the key to managing nausea and other GI side effects — most symptoms occur during dose increases and fade as the body adjusts. The three maintenance doses studied in the phase 3 trials were 5, 10, and 15 mg once weekly. The drug has a half-life of about 5 days, which is why it can be taken once a week. It is only administered by subcutaneous injection; no oral form has been studied in the phase 3 programme. The dosing information on this page comes from the FDA prescribing information and the published clinical trial protocols — it describes what was studied and what is labeled, not a personal recommendation.

Tirzepatide dose: the FDA-labeled titration schedule

The tirzepatide dose as labeled by the FDA proceeds in a stepwise titration ^[15]:

• Starting dose: 2.5 mg subcutaneous injection once weekly (4 weeks).
• Dose increase ladder: 2.5 mg → 5 mg → 7.5 mg → 10 mg → 12.5 mg → 15 mg, each step maintained for at least 4 weeks before increasing, as tolerated.
• Maintenance doses: 5 mg, 10 mg, or 15 mg once weekly. The prescribing information allows any of the three maintenance doses; the phase 3 SURPASS and SURMOUNT programmes used 5, 10, and 15 mg as their fixed maintenance comparisons.
• Maximum labeled dose: 15 mg once weekly.

The stepwise titration is specifically designed to manage the gastrointestinal adverse effects — nausea, vomiting, diarrhoea, constipation — that are most common during dose escalation and that generally ease with continued exposure ^[15].

Tirzepatide dosage is identical across the type 2 diabetes and obesity indications in the FDA label: the same 2.5 mg start, same titration schedule, same 15 mg maximum.

Tirzepatide injection: route and administration

The tirzepatide injection is subcutaneous — administered under the skin — not intravenous or intramuscular. The only route studied in the phase 3 programme is subcutaneous injection; no oral formulation has entered the phase 3 programme for tirzepatide (in contrast to semaglutide, where an oral form exists).

Injection sites per the label: abdomen, thigh, or upper arm. Rotating injection sites is recommended to reduce local reactions (redness, bruising, tenderness) at the injection site ^[15]. A tirzepatide injection is given once weekly on the same day each week. If a dose is missed and it is within 4 days of the scheduled dose, it may be administered; otherwise it is skipped and the next dose taken at the regularly scheduled time, per label guidance ^[15].

Marketed formulations are refrigerated; the specific reconstitution and storage parameters are formulation-dependent. Clinical trial product was a subcutaneous solution.

Pharmacokinetics: half-life and albumin binding

Elimination half-life: approximately 5 days in humans ^[1]. This long half-life is the direct result of the fatty-diacid arm attached to the lysine at position 20 of the peptide chain, which confers high albumin affinity — the peptide binds reversibly to albumin in the bloodstream, which dramatically slows renal clearance and proteolytic degradation ^[1].

Time to steady state: approximately 4 weeks of once-weekly administration, consistent with the approximately 5-day half-life ^[1].

Population PK: tirzepatide exposure increases proportionally with dose across the studied range. Hepatic impairment does not appear to meaningfully alter pharmacokinetics; population PK analyses across the SURPASS programme support the same dose schedule across the studied populations.

Gastric emptying effect: tirzepatide transiently delays gastric emptying to a degree similar to selective long-acting GLP-1 receptor agonists, with this effect attenuating during continued dosing ^[23]. This pharmacodynamic property is one of the mechanisms of appetite reduction and is also the basis of the perioperative aspiration caution.

Drug interactions: the gastric-emptying delay may reduce the rate (but generally not extent) of absorption of oral concomitant medications, including oral hormonal contraceptives. The FDA label advises additional or alternative contraceptive methods during dose initiation and escalation ^[15].

Doses studied in the phase 3 programme: tirzepatide dosage context

The SURPASS programme (type 2 diabetes) and SURMOUNT programme (obesity) used three fixed maintenance doses — 5, 10, and 15 mg once weekly — in their primary efficacy analyses. Effect sizes were dose-dependent across both programmes.

In SURPASS-2 (n=1879, 40 weeks, T2DM): tirzepatide 5 mg produced HbA1c reduction of 2.01 percentage points; 10 mg, 2.24 pp; 15 mg, 2.30 pp — all superior to the comparator arm at 1.86 pp ^[3].

In SURMOUNT-1 (n=2539, 72 weeks, obesity without T2DM): mean body-weight change at week 72 was -15.0% (5 mg), -19.5% (10 mg), -20.9% (15 mg) versus -3.1% with placebo ^[4].

In SURMOUNT-J (Japan, n=225, 72 weeks, obesity without T2DM): estimated treatment differences versus placebo were -16.1% (10 mg) and -21.1% (15 mg) in body weight ^[41].

Gastrointestinal adverse events were the most common and were dose-related, most frequent during the titration phase. The proportion of participants who discontinued because of adverse events was greater at higher doses ^[4]. The pharmacovigilance record from post-market FAERS data identified gastrointestinal events and incorrect dose administration as the most frequently reported categories ^[31].