I'm sure you have noticed the similarities on the labeling of many drugs. Let's look at testosterone for example. One can find compounds like testosterone cypionate, enanthate, propionate, heptylate; caproate, phenylpropionate, isocaproate, decanoate, acetate and the list goes on and on. In all such cases the parent hormone is testosterone, which had been modified by adding an ester to its structure. One of the most misunderstood subjects in the world of steroids is the ester.

An ester is a chain composed primarily of carbon and hydrogen atoms. This chain is typically attached to the parent steroid hormone at the 17th carbon position (beta orientation). Esterification of an injectable anabolic/androgenic steroid basically accomplishes one thing: it slows the release of the parent steroid from the site of injection.

By slowing the release of the parent steroid the compound would remain active in the body for a very short period of time.

Different esters exist for various compounds. Different esters give compounds different clearance times in the blood. All over the internet, you will find different (unreferenced) information on the half-life of compounds. A lot of the confusion comes from a lack of understanding on a compound's half-life versus it's biological or terminal half-life. For our purposes, we really only care about the terminal half-life, defined as:

*The biological half-life or elimination half-life of a substance is the time it takes for a substance to lose half of its pharmacologic, physiologic, or radiologic activity, as per the MeSH definition.

Ester Half-life Terminal Half-life

Suspension within 1 hour
Acetate 3 days 1 day
Propionate 2 days 0.8 days
Phenylpropionate 4.5 days 1.5 days
Butyrate 2-3 days
Valerate 3 days
Hexanoate 3 days
Caproate 4-5 days
Isocaproate 9 days 4 days
Heptanoate 5-6 days
Enanthate 10.5 days 4.5 days
Cypionate 6-7 days 5 days
Octanoate 6-7 days
Nonanoate 7 days
Decanoate 15 days 7.5 days
Undecylenate 8-9 days 14 days
Undecanoate 16.5 days 20.9 days

IMPORTANT NOTE: These half-lives are approximations, and may vary slightly depending on injection site, carrier oil, and other factors. There isn't any pharmacokinetics studies done on the majority of AAS.

Long chain esters, such as Cypionate, Decanoate, Enanthate, etc. possess a much heavier molecular weight than short chain esters. Consequently, on a mg for mg basis, you are receiving far extra mg of steroid in a short estered compound as opposed to a large estered compound.

Listed below is the percentages of the actual hormones for each ester:

Ester % Of The Actual Hormone

Acetate 87%
Propionate 80%
Phenylpropionate 66-67%
Isocaproate 72%
Enanthate 70%
Cypionate 69%
Decanoate 62%
Undecylenate 61%
Undecanoate 61%