Antidepressants -- particularly selective serotonin reuptake inhibitors (SSRIs) -- are some of the best-known culprits responsible for low libido and impaired orgasm. Certain chemicals in the brain affect your libido. SSRIs raise serotonin in the blood, which can reduce your libido. In fact, SSRIs may be used "off-label" to treat men with premature ejaculation since it slows down their sexual excitement. Other culprits include prescription drugs that lower blood pressure, which can interfere with nerve signals, and antihistamines, which can dry up not only your runny nose but your vaginal lubrication as well, making sex uncomfortable.