Sex. It Really Is Chemistry.

What makes sex feel so good? What ignites passion and sustains attachment? What is it that makes your heart flutter? And how can you keep those feelings alive, especially in the bedroom, after 10—or 40—years?

Turns out passion and attraction—all the stuff of poetry, song, and story—are the product of your most ancient brain—the limbic system—which you have in common with lots of other animals and which regulates a chemical stew of neurotransmitters. Emotions, drives, impulses, and desires originate in the limbic system. This part of the brain is wired for pleasure and passion, and it operates independently of our conscious choice or will.

Now, just for the record, I refuse to believe that our primitive mammalian brain and a bunch of electrochemical impulses is all there is to love and romance, but a good part of what maintains a relationship and makes sex feel good is indeed all about the chemicals.

The neurochemicals in the brain have two evolutionary goals: to encourage reproduction and then to help maintain a sufficiently nurturing environment for offspring.

Sex is supposed to feel good so that you have lots of it and fulfill your evolutionary mandate to multiply. We wouldn’t last long as a species if sex felt bad. But lots of casual sex and many partners is counterproductive for the long and challenging process of raising children. So your neurochemical circuitry is finely tuned to make sex pleasurable, but also to reinforce the bonds with your mate.

And even though your children may be grown and gone, you still operate within that chemical framework. So you might as well understand it and use it to your advantage.

If you find something pleasurable, sex for example, or chocolate—or sex and chocolate—it’s because your limbic system releases a rush of dopamine when you indulge in what you crave. Dopamine drives people to fulfill their cravings. In one well-known study a rat receives a spurt of dopamine every time it presses a lever. Soon, the rat is obsessively pressing the lever, no longer eating, copulating, or tending to its pups.

Orgasm releases a big surge of dopamine.

Like the rat, you can’t exist on that tingly dopamine high, however good it feels. When there’s too much dopamine in the circuit, the brain begins to reduce the levels it produces and to shut down dopamine nerve receptors. That’s why addicts need an ever-increasing “fix”—more of the drug, sex, porn, or gambling—to reach the same high.

So, immediately after orgasm, dopamine levels drop and prolactin is released to calm things down, especially in males. Prolactin is the dopamine antidote. This is what regulates the “recharge” time in younger men (remember when?); it produces a feeling of sexual satisfaction—and sleepiness, which is why men tend to roll over and fall asleep.

So, don’t take it personally; it’s just the prolactin talking.

Endorphins are also released during sex. These are opioid-like neurochemicals, like morphine and heroin, that block pain and induce feelings of euphoria. They’re also released when you laugh or exercise. (That’s what’s responsible for the “runner’s high.”)

Vasopressin, another neurochemical released during sex, encourages bonding behavior. When vasopressin is suppressed in male prairie voles, a mammal that forms monogamous pairs, they tend to lose their sense of connectedness and become disinterested in their mate.

But the most important chemical that balances the irresistible dopamine “high” is oxytocin. This is the “cuddle hormone”; it makes you feel close and loving. It calms you and relieves stress. And unlike dopamine, you can never get enough of it.

Oxytocin is released during sex, but it’s also released during labor and lactation to create that instinctive bond between mother and baby. During sex, it reinforces your connection with your mate. It offsets the opioid-like cravings of dopamine and endorphins while making the two of you feel close and receptive to sex.

Evidence even suggests that when you have more oxytocin in your system, more nerve receptors are created just to accommodate them. So be sure to laugh, exercise, make love, and cuddle before and after (if your mate can stay awake) to create lots of receptors for your increased oxytocin levels.

And in order to increase your sensitivity to the dopamine and endorphin “high,” cuddle without the sex occasionally. Take a little sex break so that when you come together, your pleasure circuitry is primed and ready.

Your body is hard-wired for sex in the most primitive levels of the brain. When you make love, you’re producing the most potent chemicals your system is capable of. You are a sexual animal. Celebrate!