Androgens are male hormones found in both males and females. Generally speaking, the higher the androgen level in the body, the more acne that results. Anti-androgens are just what they sound like--medications that work to reduce the level of androgens in the body. They are oral prescription medications that doctors or dermatologists sometimes prescribe to females with acne, particularly when a blood test shows abnormally high levels of male hormones. They are almost never prescribed to males because they can feminize the body, causing breast growth, and other undesirable side effects.
Anti-androgens are normally prescribed alongside oral contraceptives (birth control pills), which are also a hormonal treatment for acne that keeps androgens in check, but can be prescribed on their own as well. The most commonly prescribed anti-androgen is spironolactone.
All hormonal treatments, including both anti-androgens and oral contraceptives come with side effects, and should only be introduced under close partnership with a trusted physician.