Primo E - anabolic, modified dihydrotesto sterone. It is characterized by the addition of a double bond between carbons 1 and 2, which helps to stabilize the 3-keto group and anabolic increases, the addition of 1-methyl group that protects against steroid metabolism in the liver. In use Primo depot enantatny ester attached to Primo through 17-beta hydroxyl group (17b-hydroxy-1-methyl-5a-androst-1-en-3-one), the chemical formula C20H30O2. Esterified steroids are not as polar as free, they are absorbed less quickly from the injection site.

Primo presents an interesting situation with regard to stacking. Pharmacologically there is probably no difference in stacking behavior compared to M' Asteron, and certainly no important difference, but in practice those who wish to use Primo almost always are looking for mild stacking choices as well. For this reason, though D'bol, Anad, or testo sterone are effective stacking choices, they usually are not combined with Primo.