A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Why do men feel sleepy after sex?

December 22, 1995

Dear Cecil:

Is there a biological reason for men to feel sleepy after orgasm? My girlfriend says there is some scientific basis for this. If so, is there any hypothesized rationale for this occurrence in terms of human evolution?

Cecil replies:

Before we drag Darwin into it, Chuck, we'd better make sure we have a genuine phenomenon on our hands. It's true everybody thinks men get sleepy after sex. Pioneer sex researcher Alfred Kinsey wrote, "A marked quiescence of the total body is the most widely recognized outcome of orgasm." One might object that the most widely recognized outcome of orgasm is the one you have to put diapers on. Still, when Kinsey goes on about "a [postcoital] calm, a peace, a satisfaction with the world," coupled in some quarters with a desire to set fire to tobacco, most men and, for that matter, most women know what he's talking about. It's just that whereas women see this tranquil state as a chance to cuddle and talk, guys tend to look at it as a cure for insomnia — sometimes literally. When a man over 40 talks about trying to sleep with women, he's not necessarily using a figure of speech.

But let's get down to the physiological facts of the situation. While sex might mellow you out, does orgasm really make men (or anybody) sleepy? The medical literature on the subject is not voluminous, but I did turn up one study conducted, fittingly, by ze French (Brissette et al, 1985 — from Quebec, actually). The researchers signed up five male and five female volunteers to engage in sexual activity. This wasn't as much fun as it sounds. Number one, the sexual activity to be engaged in was masturbation. Number two … well, let me quote from the report: "At 11:00 PM, after placement of the electrodes and thermistors, subjects retired to their room and the anal probe was inserted. … The anal probe transmitted pressure changes in the anal canal to a transducer connected to a DC amplifier. … The use of this anal probe gave an objective account of the orgasm in both men and women." The electrodes and thermistors, meanwhile, recorded heart and respiratory rate. The things one does for science.

Anyway, on successive nights the test subjects performed one of the following procedures: (1) Read "neutral material" while sitting in bed for 15 minutes "after which the probe was withdrawn and the lights turned out." (2) Masturbate for 15 minutes without reaching orgasm. Yank probe, douse lights. (3) Masturbate for 15 minutes, reach orgasm. Decide you like probe, ask that voltage be turned up. Told to bugger off, experiment over. Results tabulated. Conclusion: sex or the lack of it made absolutely no difference in how soon and how well you slept afterward.

The researchers conceded that the experimental design was open to criticism on various grounds, the most telling in my opinion being that it was incredibly stupid. Suppose you were one of the male subjects on night three. Having on the previous night been subjected to a severe case of cyanotic spheroids, you're now lying there postejaculatively in … well, let's say you're in a state of disarray. In comes some guy in a white lab coat to roll you over and extract a hot-wired turkey baster from your sphincter ani. Does this put you in a state of mind conducive to sleep? On the contrary, you're expecting them to tell your folks to come take you home from summer camp. So maybe these results shouldn't be taken with 100 percent seriousness. But right now they're all we've got.

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