Many anabolic steroids have the ability to increase estrogen levels due to the aromatase process, specifically the conversion of testosterone to estrogen. This can lead to gynecomastia and water retention. Excess water retention can also promote high blood pressure when it becomes severe. Steroids that do not carry a strong estrogenic nature can also cause these effects, most notably gynecomastia if they carry a progestin nature. A prime example would be Nandrolone, which while it aromatizes only does so at 20% the rate of testosterone. However, it also carries a strong progestin nature, and progesterone has been well noted for carrying the ability to stimulate the estrogenic mechanism in the mammary tissue. By administering Aromasin during the use of anabolic steroids, this will inhibit the aromatase process, lower estrogen levels and protect the individual from estrogenic side effects.