How do you protect yourself against this? Well, when taking Deca Durabolin you can also take ant-estrogen medications to counter the results. Things like Nolvadex and Arimidex are popular choices. Both approach limiting the effects of estrogen different and will have different side effects on your health worth considering. Even with side effects though it is still worth pursuing either of these options. Gynecomastia is a particularly big problem due to how the imbalance between estrogen and progesterone is what leads to gynecomastia. So, by keeping your hormone levels regulated, you reduce the risk of potential unwanted growth.
The 5α-reductase enzymes that perform this reaction ( Fig. ) have broad substrate specificity for steroids containing a Δ 4 ,3-keto configuration, including progesterone and 17α-hydroxyprogesterone, which are better substrates than testosterone  . The reaction exhibits an absolute cofactor requirement for NADPH, which provides the hydride ion for carbon-5, whereas a proton from water is transferred to carbon-4  . The 4B-hydrogen of the nicotinamide ring of NADPH is preferentially incorporated rather than the 4A-hydrogen  . All attempts to reverse the reaction using mammalian enzymes have been unsuccessful; whereas the first step in reversal (enolization of carbon-4) can take place, the energy barrier for abstraction of the hydride from carbon-5 is extremely high  . Reduction to a 5α-stereochemistry rearranges the A and B rings to make the steroid molecule flatter and less polar.