Why are weekly injections common for testosterone replacement therapy (TRT)?

The goal of treatment is to find a steady state testosterone level to minimize the peaks and valleys of treatment. Patients on extended intervals between injections often experience higher than optimal levels early on after injection (the peak) and a drop in therapy benefits before their next injection (the valley).The half life of testosterone cypionate is 7-8 days. Half of the dose is present in the body one week after injection. As stated earlier, some patients are able to maintain levels on a 10-14 day cycle but the vast majority achieve better results on a weekly basis.