Often accused of lack of sex or condemned by their partner for lack of interest, a large number of men succumb to fatigue after sex and fall asleep quickly. Deprived of caresses after the act of love, the fairer sex sometimes has a hard time accepting the fact that the male organism is subject to the multitude of compounds that are released in the body and brain after sex. The main culprit behind this behavior is prolactin, a hormone associated with emotions and sexual satisfaction. Its release in the body, immediately after ejaculation, leads to relaxation and sleep. During sleep, prolactin levels are also high. Laboratory experiments with injection of prolactin in vigorous mammals also lead to inevitable fatigue. It is important to note that statistically, prolactin levels are 4 times higher after an orgasm reached during sex compared to the increase after masturbation. Masturbation is not able to cause a strong surge of prolactin, which is part of the scientific explanation for the depressive states that occur when deprived of sexual contacts. Another hormone affecting fatigue after intercourse is oxytocin – the hormone of love. It is associated with the feeling of love, the feeling of closeness and trust between partners and lowers stress, fear and tension. Lowered stress levels and increased oxytocin levels after sex are a second major factor in a man’s sleep. Vasopressin is a hormone that predisposes to another type of fatigue – that of the nervous system. In addition to playing a role in controlling blood vessels, water balance in the body, and determining some social dimensions of personality, the surge of vasopressin relaxes the muscles even more and increases the release of oxytocin in the body. Along with it, epinephrine levels rise and dopamine levels fall, resulting in physical relaxation of the entire body, improved blood circulation to the extremities, and a sense of lightness and calmness. NEWS_MORE_BOX The last factor is pure physical fatigue – often sexual intercourse lasts 20-60 minutes and more in young couples. It can be argued that the man makes much more physical effort to satisfy his partner sexually, therefore fatigue occurs to him to a much greater extent. Ladies should not misunderstand this typical male behavior – it works in their favor. According to a popular theory of sexual evolution, high levels of prolactin prevent the male organism from obeying its reproductive instinct and leading it to think or act about another partner. Evolutionary science calmly interprets the phenomenon as a manifestation of affection and positive force in the relationship between a couple.