As with all steroids, Deca can cause dangerous damage to the liver and kidneys. While its effects are generally less severe than those of some other more potent anabolics, toxicity can be severe, especially in those who use large amounts. In addition, men who use this true anabolic run the risk of gynecomastia, which is the growth of breast tissue resembling that of women. Deca is one of the steroids that is least likely to cause gynecomastia, but the possibility still exists. It also can cause blood clots and detrimental changes in the levels of cholesterol in the body. While changing cholesterol levels are not necessarily fatal, blood clots can be.