The Effects of Vaginal Stimulation on Pain Tolerance
First of all, pajiboys and pajibettes, I apologize for the spotty nature of this column over the last few weeks. After a couple of years spent trying to find an explanation for my constantly-fluctuating-but-never-good health, the doctors have run out of tests to do and have simply added the vague disorder of fibromyalgia to my other diagnoses of IBS, GERD, and vestibular migraines (actually, that last one may have just been folded into the fibromyalgia, I'm not really clear on which symptoms belong to which "separate," disorders at this point). Also I have a couple of herniated discs in my lower back, because why not? I've tried my best not to let my health affect my career as an academic scientist, but that means that when I have a bad day or week, it's the side projects that tend to get neglected. Hopefully now that I'm at the, "throw pills at it and see what sticks," point of chronic illness, things will level out a bit. In the meantime, exhaustion, lightheadedness, queasiness, and pain are part of my daily life.
Given all this, as you can probably imagine, I've tried a lot of painkillers over the years. Large doses of ibuprofen usually help when I have migraines or mild abdominal pains. Muscle relaxants sometimes help when my body decides the tie itself in knots. When my the discs in my lower back go rogue and start pinching the sciatic nerve, I can sometimes get mild relief from Tylenol, but too much of that makes my over-sensitive stomach queasy. Narcotics might help, but I wouldn't know because I can never manage to stay conscious when taking them. In all honesty, there is only one thing I know of that can really help when the pain is terrible; that actually makes the most intense nerve pain disappear, at least for a little while, and loosens my muscles enough that they don't bother me anymore. And that thing is sex (and segue!). I joke that it's my panacea but it's only partially a joke. In reality, sexual activity can indeed have a strong analgesic affect, at least for women.
Several studies have shown that vaginal stimulation increases pain tolerance in women (as determined by putting painful degree of pressure on a finger) by around 40% and pain detection threshold by about 50%. Stimulation to the point of orgasm produced even more dramatic results - a pain threshold increase of about 75% and pain detection threshold increase of over 100%, although the small sample size of the study (only 10 women) means those numbers should really be taken as rough indicators, not absolute measures applicable to the whole female population. The same study found no effect on the subject's ability to detect a non-painful touch, indicating that the effect is specific to pain rather than an overall dampening of tactile sensation. A more specific study on the effect of sexual stimulation on migraine headaches found that orgasm relieved the pain of migraines for women, though as in the previously mentioned study, men weren't included (presumably because they don't have a reputation for refusing sex for headaches, but we won't get into the sexual politics of that choice). In fact, I haven't been able to find any studies that look at the effect of sexual stimulation or orgasm in men (if you know of any or just have better google skills that me, please link in the comments). The impression I'm getting from the literature is that, frankly, because women are more likely to experience pain from sex and therefore it's an advantage for them to have lessened sensitivity to pain during sex, researchers are simply more likely to study their pain responses to sexual stimulation.
One study in rats (because there are some things you can't do to human subjects) found that the analgesic affect of vaginal stimulation is related to the hormone estradiol. As in humans, vaginal stimulation raised the (apparent) pain threshold of female rats (as measured by whether they cry out when their tails were shocked). When the rats, whose ovaries had been surgically removed, were treated with estradiol, their pain tolerance increased. When the rats were given both estradiol and progesterone the effect disappeared. Estradiol is one of two forms of estrogen present in females. It is primarily produced in the ovaries, although it can also be produced in some cells (in particular, fat cells) from testosterone. Since the rats in the study had no ovaries, it's likely that while estradiol is one factor involved in increasing pain tolerance during sexual stimulation, it is not the only one.
In fact, the major male sex hormone, testosterone, which is involved in the sexual response of both sexes, also plays a role in pain tolerance. An experiment on sparrows found that the amount of time it took for the birds to remove their feet from uncomfortably hot water was increased when the birds were given testosterone and decreased when they were given agents that blocked testosterone. The researchers actually theorize that this change may be due to the above-noted conversion of testosterone to estradiol. Testosterone therapy has also been found to have a positive effect on chronic pain disorders like fibromyalgia, though it's unclear if this effect is due to testosterone itself or a related steroid synthesized from its conversion. It's also possible that the hormones that become elevated post-orgasm, most notably oxytocin and prolactin, could have a pain-reducing impact. Oxytocin in particular is not well understood (and frequently grossly mischaracterized), but could have a role in post-orgasm feelings of relaxation, which in turn could affect perceptions of pain.
In any case, the pain-reducing effects of sexual stimulation are sadly short-lived. Sex is great if you want to temporarily knock out a migraine or forget that your spine is an asshole who can't seem to stay in place (and if you're using it that way, please be careful what positions you choose), but it can't actually fix pain. For that you typically need actual medical care.