Nonylphenol can cause endocrine disruption in fish by interacting with estrogen receptors and androgen receptors. These enzymes are responsible for converting androgen hormones into estrogen and dihydrotestosterone, respectively. It is an analogue of androgen steroid hormones like testosterone and DHT. Androstenedione is the common precursor of the androgen and estrogen sex hormones. Norethisterone is a potent progestogen and a weak androgen and estrogen. It contains characteristics found in the chemical nucleus of both estrogen and androgen hormones. Hormone therapy is effective for acne even in women with normal androgen levels. The major androgen in males is testosterone. It works by decreasing the production of dihydrotestosterone (DHT), an androgen sex hormone. Higher androgen levels lead to increased expression of androgen receptor. This may additionally contribute to suppression of androgen levels by estrogens. Digit ratio in men may correlate with genetic variation in the androgen receptor gene. Decline of testosterone production with age has led to interest in androgen replacement therapy. Individuals with prostate cancer who are treated with androgen deprivation therapy may experience gynecomastia. It works as an antiandrogen mainly by acting as an androgen receptor antagonist.