Fertility refers to the ability to conceive, but infertility is a problem that may be experienced by either men or women. Up to 15 percent of couples in the United States struggle to conceive after a year of trying, according to the National Survey of Family Growth. 

There are many possible causes of infertility, including medical conditions, genetics, and environmental factors. In men, possible causes include abnormal sperm production or function; problems with delivery of sperm; smoking, alcohol, certain medications; and damage caused by cancer and cancer treatments. In women, possible causes include, among others, ovulation disorders such as hyperthyroidism; cervical or uterine abnormalities; damage to the fallopian tubes; endometriosis; early menopause; and pelvic adhesions. 

Treatment options depend on the cause of infertility but may include stimulation of the ovaries, in vitro fertilization, artificial insemination, and medication. Drug classes used to treat infertility include gonadotropins, selective estrogen receptor modulators/SERMS, pituitary hormones, antigonadotropin-releasing hormones, and other infertility agents.