Halotestin is the oral steroid with the most side effects. Fluoxymesterone puts extremely high stress on the liver and is thus potentially liver damaging. Other frequently-observed side effects are increased production of the sebaceous gland (which goes hand in hand with acne), nasal bleeding, headaches, gastrointestinal pain, and reduced production of the body's own hormones. Men who tries this steroid become easily irritable and aggressive.

Women must avoid Halotestin because this can lead to severe virilization side effects, deepening of the voice, change in sex drive, irregular menstruation or enlargement of the clitoris.