Although i’d wager most of it ends up in humans, it is still sold as a Vetrinary Steroid. As a vetrinary steroid it was never approved for human use, which makes it impossible to get a prescription for it in the usa. add this to the fact that it is a schedule 2 controlled substance in the united states and it becomes quite clear that the only way to get this steroid in the usa is to buy it on the black market. that being said, it is still relatively easy to obtain the real stuff. This is because smuggling almost 2x as much testosterone in the same space is a rather enticing thing, making it commonly available.
Testosterone Propionate also converts to both Estrogen (through Aromatization) and Dihydrotestosterone (through 5a-reduction). Most of the side effects people experience with testosterone use is actually from it’s conversion to these two substrates. Thus, hair loss , water retention, acne, and other side effects are possible with use of this drug. Conversion to these hormones is also responsible for some of testosterone’s ability to build muscle; therefore when many side effects are avoided with the use of ancillary compounds, some of the muscle building properties are also stunted.
The partition coefficient of the ester in question is important because is effects how long the drug itself stays in the system. If the testosterone transfers too quickly from the oil to the blood, the result is a sudden spike in testosterone which then rapidly drops once the dose has been used up. In the example of free testosterone injected into the muscle from a water suspension (as in Aquiviron, mentioned above), the testosterone is essentially immediately available to the bloodstream due to its low partition coefficient, and thus there is an immediate spike of testosterone which is used up quickly in the body.