The activity of boldenone is mainly anabolic, with a low androgenic potency. The drug is commonly used in doping within bodybuilding, even though this use is illegal. If intended to assist in bodybuilding, the drug is taken as part of a steroid stack of other anabolic steroids, usually with a potent androgen like testosterone as the 'base' of the stack. Boldenone is an androgen that differs from 17b-testosterone (17b-T) by only one double bond at the 1-position, and the removal of the methyl group protecting the 17-OH group allows it to be orally active.
The double bond of cycloartenol (compound 7 in diagram) is methylated by SAM to give a carbocation that undergoes a hydride shift and loses a proton to yield a compound with a methylene side-chain. Both of these steps are catalyzed by sterol C-24 methyltransferase (Step E1 in diagram). Compound 8 is then catalyzed by sterol C-4 demethylase (E2) and loses a methyl group to produce cycloeucalenol. Subsequent to this, the cyclopropane ring is opened with cycloeucalenol cycloisomerase (E3) to form 10 . Compound 10 loses a methyl group and undergoes an allylic isomerization to form Gramisterol 11 . This step is catalyzed by sterol C-14 demethylase (E4), sterol Δ14-reductase (E5), and sterol Δ8-Δ7-isomerase (E6). The last methyl group is removed by sterol demethylase (E7) to form episterol 12 . Episterol 12 is methylated by SAM to produce a second carbocation, which loses a proton to yield 13 . This step is catalyzed by 24-methylenesterol C-methyltransferase (E8). Compound 13 now undergoes reduction by NADPH and modifications in the β-ring to form β-sitosterol.