What the FDA label and trial protocols actually specify.

Approved indications and dose ranges

The FDA-approved tirzepatide label specifies three indications, each with the same titration schedule and a slightly different maintenance dose envelope^[21]:

• Type 2 diabetes: 2.5 mg starting dose, titrated upward by 2.5 mg every four weeks or longer, to maintenance doses of 5, 10, or 15 mg subcutaneous once weekly.
• Chronic weight management (BMI at or above 30, or at or above 27 with a weight-related comorbidity): same titration schedule; maintenance 5, 10, or 15 mg once weekly.
• Moderate-to-severe obstructive sleep apnea with obesity: same titration; maintenance 10 or 15 mg once weekly^[17].

Every maintenance dose used in the SURPASS and SURMOUNT Phase 3 programs sits inside this envelope. The trials did not test doses outside it.

The titration schedule is not arbitrary. Gastrointestinal adverse events — nausea, diarrhea, vomiting — are highest during dose escalation and decrease with continued exposure^[20]. Slow upward titration is what the label uses to manage that adverse-event curve. Compressed titration schedules of the sort that have appeared in non-FDA-approved sourcing, where vials and self-drawn syringes make it easy to skip steps, have been associated with the dosing errors logged in FDA postmarket surveillance^[11].

Pharmacokinetics

Population pharmacokinetic analysis in healthy volunteers and adults with type 2 diabetes documented an elimination half-life of approximately 116 to 120 hours — around five days^[8]. Steady-state plasma concentrations are reached after roughly four weeks of once-weekly dosing. Tmax, the time to peak plasma concentration after a subcutaneous injection, falls between 24 and 72 hours.

Plasma protein binding exceeds 99 percent. The C20 fatty diacid moiety conjugated to lysine 20 of the peptide chain is what produces that high albumin binding and prolongs plasma residence^[7]. This is a deliberate design choice — without the fatty acid, the molecule would not have a once-weekly profile.

The pharmacokinetic parameters above were established for the FDA-approved injectable presentation. They have not been independently validated for compounded copies, repackaged vials, or import "research" tirzepatide. A product with the same labeled strength but a different impurity profile, salt form, formulation matrix, or fatty-acid attachment may not produce the same plasma concentration profile, even if it produces some concentration profile.

Routes, injection sites, and stability

Subcutaneous injection is the sole approved and studied route^[22]. The label permits injection into the abdomen, thigh, or upper arm, with site rotation recommended.

The FDA-approved tirzepatide product is supplied as single-dose pens or single-dose vials. The single-dose format constrains the dosing error that can occur per administration — a critical design choice that is not preserved by the multidose vial plus patient-drawn syringe format that became common during the compounding window^[10].

Stability per the approved labeling: refrigerated storage at 2 to 8 degrees Celsius until use; room-temperature storage at or below 30 degrees Celsius is permitted for up to 21 days. These stability parameters were established for the FDA-approved presentation and are not directly transferable to other formulations.

Cold-chain handling matters because peptide therapeutics degrade meaningfully at sustained elevated temperatures, and degradation products are not the same molecule. A product that arrives at ambient temperature with no cold-chain packaging is, regardless of what is printed on the box, a product that has been outside its established stability envelope.

Co-administered medications studied

Several SURPASS trials studied tirzepatide on top of standard background therapy. Metformin was co-administered in many of the SURPASS arms with no clinically significant pharmacokinetic interaction observed and complementary mechanism (insulin sensitization)^[10]. SGLT2 inhibitor combinations have been studied for additive HbA1c, weight, and cardiorenal benefit. SURPASS-5 included background insulin glargine; insulin dose reduction at tirzepatide initiation is the documented strategy for mitigating hypoglycemia risk in that population^[10].

The label and the trial protocols are the primary references for any prescribing decision. This page is a reference summary, not a clinical recommendation.