# Tirzepatide Dosage and Dosing Research: What the Clinical Programme Studied > Tirzepatide dosage as studied in the SURPASS and SURMOUNT clinical programme: the FDA-labeled 2.5 mg start, titration schedule, maintenance doses, half-life, and route. Cited to primary sources. ## The short version Tirzepatide dosage in approved clinical use begins at 2.5 mg once weekly — a low starting dose to let the body adjust — and is increased in steps every four weeks. The three maintenance doses studied in the main phase 3 trials were 5 mg, 10 mg, and 15 mg once weekly. The drug is given as a subcutaneous (under-the-skin) injection. Its half-life — the time it takes for the body to clear half the drug — is approximately five days, which is why once-weekly dosing is sufficient. This page describes the dose ranges, titration schedule, and pharmacokinetics as documented in the FDA-approved prescribing information and the published clinical trial literature. This is not a prescription or a recommendation; all dosing decisions belong to a qualified prescriber. ## Tirzepatide dosage — the FDA-labeled titration schedule The approved prescribing information for tirzepatide describes a stepwise titration initiated at 2.5 mg once weekly subcutaneously [7]. The dose is increased in increments of 2.5 mg every four weeks. The three maintenance doses evaluated across the SURPASS and SURMOUNT phase 3 programmes were 5 mg, 10 mg, and 15 mg once weekly. The 2.5 mg starting dose is an initiation dose only, not used as a maintenance dose in the trials; its purpose is tolerability during the first four weeks. The full titration ladder as studied in the phase 3 programme: 2.5 mg (weeks 1–4), then 5 mg (weeks 5–8), with optional further escalation every four weeks — 7.5 mg, 10 mg, 12.5 mg — up to a maximum 15 mg once weekly. In the SURMOUNT-5 head-to-head trial, participants were titrated to their maximum tolerated dose within the range 10–15 mg [4]. All dosing is by subcutaneous injection; this is the only route in the approved clinical trial programme. No oral formulation of tirzepatide has been approved [7]. ## Tirzepatide dose and efficacy across the SURPASS and SURMOUNT programmes Across the SURPASS type 2 diabetes programme, all three maintenance tirzepatide doses produced clinically meaningful reductions in HbA1c. In SURPASS-2 (n=1,879; 40 weeks), HbA1c reduction was 2.01 percentage points at 5 mg, 2.24 at 10 mg, and 2.30 at 15 mg — all superior to semaglutide 1 mg (1.86 percentage points). Body weight reduction was greater at each dose: -7.6, -9.3, and -11.2 kg at 5, 10, and 15 mg versus -5.7 kg with semaglutide [2]. In the SURMOUNT-1 obesity trial (n=2,539; 72 weeks), the dose-response relationship for weight was similarly clear: -15.0% at 5 mg, -19.5% at 10 mg, and -20.9% at 15 mg versus -3.1% with placebo. Gastrointestinal adverse events occurred predominantly during dose escalation at all three maintenance doses [3]. For older adults (≥65 years) with type 2 diabetes and lower BMI (below 30 kg/m²), a post hoc SURPASS pooled analysis found meaningful HbA1c reductions of -1.97% to -2.10% across doses, without an increase in hypoglycaemia risk regardless of background insulin or sulfonylurea use [29]. ## Pharmacokinetics — half-life and once-weekly dosing rationale The approximately five-day elimination half-life of tirzepatide is the pharmacokinetic basis for its once-weekly dosing regimen [10]. This extended half-life is conferred by the C20 fatty diacid modification — eicosanedioic acid attached via a linker to the peptide backbone — which produces high albumin-binding affinity, dramatically slowing the compound's clearance from circulation compared with unmodified peptides. A population pharmacokinetics analysis of tirzepatide exposure across the phase 3 programme characterised the half-life distribution and confirmed the consistency of once-weekly dosing across the patient populations studied [10]. A dedicated pharmacokinetic study found that hepatic impairment did not produce clinically meaningful changes in tirzepatide exposure that would warrant dose adjustment [28]. The once-weekly subcutaneous injection route — the only route in the phase 3 programme — provides stable steady-state drug exposure. Marketed formulations require refrigeration; specific storage and reconstitution parameters are formulation-specific and outside the scope of the efficacy literature. ## Tirzepatide injection — administration in the clinical programme The tirzepatide injection studied in the phase 3 programme was administered subcutaneously once weekly. Injection sites in clinical trials included the abdomen, thigh, and upper arm — consistent with standard subcutaneous injection practice. Rotating injection sites is the standard approach to minimise local reactions. Injection site reactions — redness, pain, bruising, and small lumps at the site — were among the commonly documented adverse events in FAERS pharmacovigilance data, accounting for a substantial proportion of post-market reports [15]. The FAERS analysis also identified incorrect dose administration as a major signal, underscoring the importance of understanding the device and titration schedule before beginning treatment [15]. The clinical trial programme used tirzepatide formulated as a subcutaneous solution. No intravenous, oral, or intranasal route was studied in the phase 3 programme. The prescribing information contains the formulation-specific storage and administration guidance. --- An independent regulatory reading desk — the tirzepatide approval and trial record, cited to source, with no clinical role held.