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.
Far more than the other testosterone esters, for the possible exception of Sustanon, users of testosterone propionate will often complain of injection site irratation and swelling 2 . Some individuals find that the reaction that they experience with the ester is so bad in fact that they will have to cease administration of the compound. As well, due to the frequent injections of the compound and the possibility of injection site irritation, it is advisible that users rotate injection sites as frequently as possible so that no complications arise.