Dianabol (D-bol), being moderately androgenic, will produce side effects. For starters the drug can be quite estrogenic in some users. Gynecomastia (swelling of the nipple region) is often a concern during use, and may occur quite early in the cycle (particularly if the individual used high dosages). For this reason many bodybuilders add an estrogen blocker such as Nolvadex, to their cycles. Another cosmetic side effect is water retention. This is a concern for competitive bodybuilders, as it will cause a notable loss of muscle definition.

Besides gynecomastia and water retention D-bol can produce such androgenic side effects as oily skin, acne and body/facial hair growth. There is also the possibility of aggravating male pattern baldness in individuals genetically predisposed for this condition.

Like all oral steroids, D-bol has been C-17 alpha alkylated (chemically modified at the 17th carbon position on its nucleus). While this modification protects the drug from being deactivated by the liver, it can also be toxic to the organ. Long-term exposure to C-17 alpha alkylated substances can result in damage and possibly even the development of certain forms of cancer.