The time it takes to reach peak blood levels after a dose—how fast the drug kicks in.Tmax (time to maximum concentration) is the time point at which Cmax is achieved following drug administration. For subcutaneous peptide injections, Tmax typically ranges from 30 minutes to several hours depending on molecular weight, formulation, and injection site perfusion. Tmax influences dosing timing recommendations—for example, GH secretagogues are typically administered before bedtime so that peak peptide levels coincide with the natural nocturnal GH secretory window.