Post-coital tristesse (PCT) is the feeling of sadness, anxiety, agitation, or aggression after sexual intercourse. Its name comes from New Latin "postcoitalis" and French "tristeesse", literally "sadness". Many people with PCT may exhibit strong feelings of anxiety lasting from five minutes to two hours after coitus.

The phenomenon is traced to the Roman surgeon, Galen, who wrote, "Every animal is sad after coitus except the human female and the rooster." The philosopher Baruch Spinoza in his "Tractatus de Intellectus Emendatione" writes, "For as far as sensual pleasure is concerned, the mind is so caught up in it, as if at peace in a [true] good, that it is quite prevented from thinking of anything else. But after the enjoyment of sensual pleasure is passed, the greatest sadness follows. If this does not completely engross, still it thoroughly confuses and dulls the mind."

With respect to symptoms in women, one study involved an epidemiological survey of post-coital psychological symptoms in a United Kingdom population same of female twins. They found that 3.7% of women reported suffering from recent PCT and 7.7% suffering PCT for a longer time.

PCT is a separate phenomenon from the refractory period. PCT is different in that it occurs only after sexual intercourse and does not require an orgasm to occur, and in that its effects are primarily emotional rather than physiological. Some doctors prescribe serotonin reuptake inhibitors, such as fluoxetine, to treat PCT. After two weeks, people reported that "while sex was less intensely pleasurable, no emotional crash followed."

One study reported that almost half of female university students reported PCT symptoms at least once in their lifetime. The study also reported that there appeared to be no correlation between PCT and intimacy in close relationships.

Another study reported that among a sample of 1208 male participants, 40% of them had experienced PCT once in their lifetime, and 20% reported experiencing PCT in the four weeks preceding the study. This study also reports that between 3-4% of the sample experienced PCT symptoms on a regular basis. According to the same study, PCT among males is associated with current psychological distress, sexual abuse during childhood, and with several sexual dysfunctions.