A Primer On Esters And How They Work
One of the most misunderstood subjects in the world of steroids is the ester--the mechanism by which injectable esterified steroids like testosterone cypionate, testosterone enanthate, and Sustanon work. If you take a quick look around the Internet you will probably find countless articles that consider one form of a steroid far more effective than another. Arguments over the superiority of cypionate to enanthate, or Sustanon to all other testosterones are of course very common. Such arguments are in all practicality, baseless. In this report we'll take an authoritative look at the ester and what specifically it does to a steroid.

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), although some compounds do carry esters at position 3 (for the purposes of this article it is not crucial to understand the exact position of the ester). Esterification of an injectable anabolic/androgenic steroid basically accomplishes one thing, it slows the release of the parent steroid from the site of injection. This happens because the ester will notably lower the water solubility of the steroid, and increase its lipid (fat) solubility. This will cause the drug to form a deposit in the muscle tissue, from which it will slowly enter into circulation as it is picked up in small quantities by the blood. Generally, the longer the ester chain, the lower the water solubility of the compound, and the longer it will take to for the full dosage to reach general circulation.

Slowing the release of the parent steroid is a great benefit in steroid medicine, as free testosterone (or other steroid hormones) previously would remain active in the body for a very short period of time (typically hours). This would necessitate an unpleasant daily injection schedule if one wished to maintain a continuous elevation of testosterone (the goal of testosterone replacement therapy). By adding an ester, the patient can visit the doctor as infrequently as once per month for his injection, instead of having to constantly re-administer the drug to achieve a therapeutic effect. Clearly without the use of an ester, therapy with an injectable anabolic/androgen would be much more difficult.

Esterification temporarily deactivates the steroid molecule. With a chain blocking the 17th beta position, binding to the androgen receptor is not possible (it can exert no activity in the body). In order for the compound to become active the ester must therefore first be removed. This automatically occurs once the compound has filtered into blood circulation, where esterase enzymes quickly cleave off (hydrolyze) the ester chain. This will restore the necessary hydroxyl (OH) group at the 17th beta position, enabling the drug to attach to the appropriate receptor. Now and only now will the steroid be able to have an effect on skeletal muscle tissue. You can start to see why considering testosterone cypionate much more potent than enanthate makes little sense, as your muscles are seeing only free testosterone no matter what ester was used to deploy it.

Actions Of Different Esters
There are many different esters that are used with anabolic/androgenic steroids, but again, they all do basically the same thing. Esters vary only in their ability to reduce a steroid's water solubility. An ester like propionate for example will slow the release of a steroid for a few days, while the duration will be weeks with a decanoate ester. Esters have no effect on the tendency for the parent steroid to convert to estrogen or DHT (dihydrotestosterone: a more potent metabolite) nor will it effect the overall muscle-building potency of the compound. Any differences in results and side effects that may be noted by bodybuilders who have used various esterified versions of the same base steroid are just issues of timing. Testosterone enanthate causes estrogen related problems more readily than Sustanon, simply because with enanthate testosterone levels will peak and trough much sooner (1-2 week release duration as opposed to 3 or 4). Likewise testosterone suspension is the worst in regards to gyno and water bloat because blood hormone levels peak so quickly with this drug. Instead of waiting weeks for testosterone levels to rise to their highest point, here we are at most looking at a couple of days. Given an equal blood level of testosterone, there would be no difference in the rate of aromatization or DHT conversion between different esters. There is simply no mechanism for this to be possible.

There is however one way that we can say an ester does technically effect potency; it is calculated in the steroid weight. The heavier the ester chain, the greater is its percentage of the total weight. In the case of testosterone enanthate for example, 250mg of esterified steroid (testosterone enanthate) is equal to only 175mg of actual testosterone. 75mg out of each 250mg injection is the weight of the ester. If we wanted to be really picky, we could consider enanthate slightly MORE potent than cypionate (I know this goes against popular thinking) as its ester chain contains one less carbon atom (therefore taking up a slightly smaller percentage of total weight). Propionate would of course come out on top of the three, releasing a measurable (but not significant) amount more testosterone per injection than cypionate or enanthate. [See

Esters Active Half-Life Table
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 (for example a metabolite, drug, signaling molecule, radioactive nuclide, or other substance) to lose half of its pharmacologic, physiologic, or radiologic activity, as per the MeSH definition.

Reference study.

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
Esters And The Active Dose
It is important for every person to understand that the ester which is attached to any injectable anabolic steroid possesses a certain percentage amount of the total molecular weight of the molecule. Therefore, for example, 100mg of Testosterone Enanthate is not 100mg of pure Testosterone. The reality is that you are receiving less Testosterone than most of you think, and once the ester has been removed through the esterase enzyme, the amount of pure un-esterified Testosterone left over is very different depending on the ester in question that was previously attached to the hormone.

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. As an example, there exists a larger amount of mg of Testosterone in 100mg of Testosterone Propionate than 100mg of Testosterone Enanthate. This is due to the shorter, and therefore lighter weight of the Propionate ester in comparison to the larger and therefore much heavier Enanthate ester. Many individuals just do not realize this, and should always consider this factor as one of the factors involved in the decision making process concerning which ester variant of any given compound to use during a cycle.

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

Testosterone Ester % Of The Actual Hormone
Acetate 87%
Propionate 80%
Phenylpropionate 66-67%
Isocaproate 72%
Enanthate 70%
Cypionate 69%
Decanoate 62%
Undecylenate 61%
Undecanoate 61%
Milligrams below are the estimated amount of active hormone per 100 mg of compound.

Compound Ester Pure Hormone
Boldenone (EQ) base 100 mg
Boldenone (EQ) acetate 83 mg
Boldenone (EQ) Propionate 80 mg
Boldenone (EQ) Cypionate 69 mg
Boldenone (EQ) Undecylenate 61 mg
Clostebol Base 100 mg
Clostebol Acetate 84 mg
Clostebol Enanthate 72 mg
Drostanolone (Masteron) Base 100 mg
Drostanolone (Masteron) Propionate 80 mg
Drostanolone (Masteron) Enanthate 71 mg
Methenolone (Primobolan) Base 100 mg
Methenolone (Primobolan) Acetate 82 mg
Methenolone (Primobolan) Enanthate 71 mg
Nandrolone Base 100 mg
Nandrolone Cypionate 69 mg
Nandrolone (NPP) Phenylpropionate 63 mg
Nandrolone (Deca) Decanoate 62 mg
Nandrolone Undecylenate 60 mg
Nandrolone Laurate 56 mg
Stenbolone Base 100 mg
Stenbolone Acetate 84 mg
Testosterone Base 100 mg
Testosterone Acetate 83 mg
Testosterone Propionate 80 mg
Testosterone Isocaproate 72 mg
Testosterone Enanthate 70 mg
Testosterone Cypionate 69 mg
Testosterone Phenylpropionate 67 mg
Testosterone Decanoate 62 mg
Testosterone Undecanoate 61 mg
Trenbolone Base 100 mg
Trenbolone Acetate 83 mg
Trenbolone Enanthate 68 mg
Trenbolone Hexahydrobenzyl Carbonate 65 mg
Trenbolone Cyclohexylmethylcarbonate 65 mg

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