Normally, humans feel pleasure from an orgasm; upon reaching a climax, chemicals are released in the brain, and motor signals are activated that will cause quick cycles of muscle contraction in the corresponding areas of both males and females.
[1] It is thought that people with sexual anhedonia have a dysfunction in the release of the chemical dopamine in the nucleus accumbens, the brain's primary reward center.
Additionally, it is thought that depression, drug addiction, high levels of prolactin, low testosterone, and uses of certain medications might play a role in inhibiting dopamine.
[3] A sudden-onset sexual anhedonia can also be a symptom of sensory neuropathy, which is most commonly the result of pyridoxine toxicity[4] (e.g., from large doses of vitamin B6 supplements).
[12] Other drugs which may be helpful in the treatment of this condition include dopamine agonists, oxytocin, phosphodiesterase type 5 inhibitors, and alpha-2 receptor blockers like yohimbine.