Recently there has been a new arrival on the steroid scene; this one sold exclusively by online traditional AAS vendors. Marketed as “p-tren”, the active ingredient is sometimes described as propionyltrenbolone, and the marketing claims being made for it are nothing short of remarkable.
“This is a new form of oral trenbolone, and is likely, dose for dose, the second most powerful AAS next to Methyltren.”
Bold claims indeed. But do they hold water?
Firstly, it’s important to point out that it is a propenyl group (17a-prop-2-enyl), not a propionyl group. It is an allyl group; an alkene, not an ester.
In fact, the (claimed) active ingredient of “p-tren” was quickly identified from their structural description as allyltrenbolone; a veterinary steroid used to suppress estrus in female horses, more commonly known as altrenogest, and sold under the brand-name Regu-mate ®.
This week a “p-tren” customer took it upon himself to have the product tested by a friendly organic chemist. This independent testing confirmed that the “p-tren” product is, in fact, allyltrenbolone (altrenogest) as was believed.
RU 2267 (Roussel Uclaf)
Unlike trenbolone which can isomerize to 17-epitrenbolone,  altrenogest is very resistant to metabolism due to the 17a-allyl group. The metabolism of altrenogest in horses was studied in 2006 with a view to prevent it’s use as a ‘doping agent’ in horse-racing competitions – not as an anabolic, but because estrus can impair the performances of mares. In the horse, no phase 1 (hydroxylated) metabolites were detected, and altrenogest was largely excreted as glucoronide and sulfate conjugates. 
Altrenogest is a 4,9,11-unsaturated steroid (or trenbolone derivative). They tend to be very non-specific in their binding properties, typically binding to androgen, progesterone, and often mineralocorticoid receptors. 
Altrenogest differs from trenbolone in that it has an allyl substitution at carbon 17, as illustrated below.Other trenbolone derivatives include gestrinone and tetrahydrogestrinone (THG), pictured below.
One important difference between these drugs is the length of the side-chain. Altrenogest has a 3 carbon side-chain attached from the 17a position, THG and gestrinone have two carbons, while trenbolone has no side chain.
The anabolic effects of various analogues of 19-nortestosterone were tested in 1961, and the researchers found that side-chains at C17 consisting of one and two carbons were active anabolics, whereas nandrolone substituted with a 3-carbon (propyl) side-chain was devoid of anabolic and androgenic activity. Researchers at Roussel Uclaf had similar findings; steroids with bulkier 17a- side chains had weaker androgen receptor binding affinities than those with smaller substitutions.  In the image above, the relative binding affinities of trenbolone (top), methyl tren (centre) and ethynyltrenbolone (bottom) can be seen.
Allyltrenbolone was first studied by steroid researchers at the French labs of Roussel-Uclaf, who assigned it the designation RU 2267.
Roussel Uclaf tested the anabolic activity of RU 2267 (allyltrenbolone):
“Altrenogest administered subcutaneously shows weak anabolic and androgenic activity equivalent to about 1/20 of that of testosterone” (Roussel-UCLAF, personal communication) 
Whereas most designer steroids are brought to market based on the strength of studies from the 1960s showing a strong anabolic effect in rats, it’s likely altrenogest has found its way to the market based purely on its ready availability and low cost, as all available data suggests it has little to no anabolic activity at all.
Studies into the effects of allyltrenbolone in boars found that it had a) no noticable effect on anabolism, b) an extremely suppressive effect on gonadotropins and endogenous steroids (LH, FSH, and testosterone), and c) a marked negative effect on libido. 
“Our results suggest that feeding altrenogest to growing boars will: (1) delay or inhibit sexual development by preventing the normal rise in serum testosterone that occurs during testicular development, (2) inhibit testicular development and (3) have no effect on the body growth rate from 15 to 24 wk of age.” 
1988 EU legislation prohibiting the use of hormones in livestock (particularly trenbolone) effectively killed North American exportation of beef to the EU.  In 1996 the US and Canada’s complaints were heard at a panel that included scientists to provide professional advice. 
The US delegate Mr. Brinza questioned the EU scientific advisers on the wisdom of banning growth-promoters like trenbolone, yet allowing synthetic progestagens like allyltrenbolone to be used. Dr. Arnold replied:
“It has no anabolic properties and therefore there is an exemption in the EC directives concerning this substance. Although the name is suggestive, it does not have the properties of trenbolone. Allyltrenbolone is totally different from trenbolone with respect to the biological facts. It is certainly not suitable for growth promotion.” 
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