TESTOSTERONE IS AN ANDROGEN STEROID HORMONE, AND THE PRINCIPLE MALE SEX HORMONE, TESTOSTERONE PLAYS A KEY ROLE IN DEVELOPMENT OF THE MALE REPRODUCTIVE SYSTEM AND PROMOTES SECONDARY SEXUAL CHARACTERISTICS, MUSCLE GROWTH, AND BODY HAIR. DECREASED LEVEL OF TESTOSTERONE IN MEN AFFECT SEX DRIVE, STRENGTH, AND OVERALL MOOD, IN WOMEN, TESTOSTERONE PROMOTES SEX DRIVE AND ELEVATED LEVELS OF TESTOSTERONE IN A WOMEN WILL CAUSE UNWANTED HAIR GROWTH (HIRSUTISM) IN MEN DECREASED LEVELS OF TESTOSTERONE ARE ASSOCIATED WITH HYPOGONADISM (DECREASED FUNCTIONING OF THE TESTES), LOWER LEVELS OF TESTOSTERONE HAVE BEEN ASSOCIATED WITH DIMINISHED SEX DRIVE AND LOSS OF BONE DENSITY. AN ABNORMAL TESTOSTERONE CONCENTRATION CAN CAUSE PREMATURE OR DELAYED PUBERTY IN CHILDREN AND HIRSUTISM, AS WELL AS FERTILIZATION (WHEN A WOMEN DEVELOP) A MALE CHARACTERISTIC LIKE DEEP VOICE, UNWANTED HAIR) IN WOMEN.