More info on how serotonergic medications cause sexual problems (see also previous post on Venlafaxine and orgasms).
It is hypothesized that SSRI’s affect the sexual response system by raising levels of serotonin. Serotonin, a neurotransmitter, appears to have a negative impact on the desire and arousal phases of the sexual response cycle which consists of four phases including: desire, arousal, orgasm, and resolution. This seemingly occurs through its inhibition of dopamine and norepinephrine, which are other neurotransmitters.
Serotonin also appears to exert direct effects on sexual organs by decreasing sensation and by inhibiting nitric oxide. Nitric oxide is thought to be a key player in the sexual pathway as it is thought to relax smooth muscle and blood vessels and therefore allow adequate blood supply to the sexual organs. Overall, it is the interplay of these neurotransmitters that causes antidepressant-induced sexual side effects.
And, to be more specific or scientific (according to a genius I know), these meds are thought to cause sexual dysfunction by acting at the serotonin receptor type 2a, and probably by changing the function of alpha-adrenoceptors. I don’t really know enough about the different receptors and sub receptors to fully comprehend that but I thought I’d post it in case someone else can appreciate it.