Testosterone cypionate, by Elmu.

Testosterone is the prime male androgen in the body, and as such still the best possible mass builder in the world. It has a high risk of side-effects because it readily converts to a more androgenic form (DHT) in androgen responsive tissues and forms estrogen quite easily. But these characteristics also provide it with its extreme anabolic tendencies. On the one hand estrogen increases growth hormone output, glucose utilization, improves immunity and upgrades the androgen receptor, while on the other hand a testosterone/DHT combination is extremely potent at activating the androgen receptor and eliciting major strength and size gains. While not always the most visually appealing result, there is no steroid on earth that packs on mass like testosterone does.

Testosterone Cypionate is a single-ester, long-acting form of testosterone. Due to the length of its ester (8 carbons) it is stored mostly in the adipose tissue upon intra-musuclar injection, and then slowly but very steadily released over a certain period of time. A peak is noted after 24-48 hours of injection and then a slow decline, reaching a steady point after 12 days and staying there for over 3 weeks time. Of course most users of anabolics will not find adequate benefit in the use of this steady-point dose, so this product is normally injected once a week, making the very lowest dose higher than half the peak dose at any given time. This is roughly the starting blood level as well. Effective dosage for men is 250-1000 mg/week.

A long-acting testosterone ester is a must-have in any mass-building cycle.