First misconception: The weight of an ester determines the half-life. No, it is the length of an ester that AFFECTS the half-life. This is easily seen in the lack of difference in the half-lives of testosterone phenyl propionate vs. testosterone propionate. The first ester has a MW of 150 the second has a MW of 74. They have almost identical half-lives but the phenyl propionate has the weight of the phenyl group add to it but the same length of the propionate. It doesn’t make much of a difference.
Second misconception: The ester used determines the half–life, NO. I am not sure why this is so set in people’s minds but esters are only part of the picture. An ester modifies the partition coefficient but it does not determine it. The partition coefficient is a fancy term that describes the ratio of oil solubility to water solubility. Almost anything is water miscible to some part, even if very small. This includes the hormones we use as well as the ester of them. This the more lipophilic (that is oil soluble, I am simplifying here) the less LIKELY the hormone is to enter into water and be hydrolyse (hydrolysis is the term for the removal of the ester from the base, again this is a simplification of the process). That is why hormones have half-lives, their absorbs ion is based on probability and therefore follows the same pattern as decaying uranium, rolling of the dice, and cards. Contrary to popular belief this is true of the base hormones as well as the estered ones. The esters only modify the ratio (decrease the probability of going into water) For a more complete article on this (its old but still a good read) go read Invalid Link Removed. While it doesn’t go into the mechanics too much it is still the best one I have seen.
While the above is a major factor if you want an accurate estimate of the half-life have to include the solubility of the hormone base you’re using, the length of the ester, the solution that the hormone is suspended in, the biology of the person being injected, and the placement of the depot.
1st. The base solubility hormone is just that, how well it will go into solution, water or oil. What its partition coefficient is to start with. Nandrolone is more lipophobic then testosterone, therefore tends to have a shorter half live then testosterone even with the same ester (see number 2 for more info on this).
2nd. The length of an ester determines how much the partition coefficient is modified (outside of any other influences). The length is usually given in the number of carbon atoms, formate 1, acetate 2, propionate and phenyl propionate 3, butyrate 4, valerate 5, hexanoate, caproate, and isocaproate 6, heptanoate and enanthate 7, octanoate and cypionate 8, nonanoate 9, decanoate 10, undecanoate 11. What’s more the degree that the ester modifies the base per carbon increases with the ester length. To put it another way the longer the esters the more it dominates the properties. For instance the half-life of nandrolone cypionate is less then that of its testosterone counterpart but the difference between testosterone decanoate and nandrolone decanoate is nil (in theory, no one has measured the half life of nandrolone cypionate to my knowledge. But it works well in practice).
3rd. The solution that the hormone is carried in also makes a big difference. Simply put the more hydrophobic your solution your solution the harder it is for the hormone to enter into water. So if you have testosterone enanthate in caster oil with lots of benzyl benzoate you can have a half-life of around 12 days. On the other hand if you use polyethylene glycol or glycerol with no hydrophobic solvents you can have a half-life of less then 8 days. The goes for all hormones. This is due to the reduction (or induction for the hydrophilic solvents) of exposure to water. The less exposure to water the longer the half-life. The more exposure to water the shorter the half-life.
4th. The biology of the person being injected, and the placement of the depot can also affect things. The first part is simple, people with faster metabolisms process things faster then people with slow metabolisms. More enzymes and faster processing of the metabolites will break down the depot faster, this exposing more of the esters to water. Another considerate is where the depot is located. Most people don’t think of this but if you place (inject) the depot into an often-used muscle the increased agitation is going to expose more of the hormone to the water. Its like mixing two difficult to-mix liquids together, by hand is going to take a lot longer then if you use a mixer. For most people this isn’t a consideration and site rotation take care of it but it is a consideration if you’re a long distance runner shooting in the legs or a boxer shooting in the triceps. This is another reason site rotation is important; it evens out the release of the hormones.