PHARMATEST U 250 (Testosterone Undecanoate) is a very long testosterone ester with a half-life of approximately 20–30 days. Because of its long half-life, testosterone undecanoate (TU) can be conveniently utilized for hormone replacement therapy (HRT). The frequency of testosterone injections can be reduced to once every 2–3 months when using TU in HRT! Bodybuilders and other athletes can use TU as a basis for very long ("eternal") cycles, allowing a reduction in the frequency of injections while maintaining a smooth hormonal background. In the "eternal" cycle, the frequency of injections can be every 2–6 weeks. A single administration of 1000 mg TU will create a three-month foundation of testosterone at the physiologically normal level. Likewise, a dosage of 1500–2500 mg of TU per month is suitable for an eternal cycle.

With a half-life of around 3 weeks, it is a very slow-release ester, significantly slower than even PHARMATEST C 250 (Testosterone Cypionate).