Possibly the most popular steroid compound of the last few decades, Deca-Durabolin earns its reputation by producing large muscle gains, aiding with joint pain and improving the immune system. These benefits come from a substance that has a relatively low rate of side effects because it doesnâ***8364;***8482;t convert to estrogen as much as many of its counterparts. Not that Deca is without its problems. First, Deca needs to be taken over long periods of time (cycles of 12 weeks minimum) for it to be effective. Also, Deca must be taken with testosterone because the body***8217;s natural levels will drop. Testosterone should also be a part of a Deca cycle***8217;s post-cycle-therapy. Deca can also cause a good deal of water retention and acne.