In 1983, on Valentine’s Day, psychiatrist Michael Liebowitz published The Chemistry of Love, in which he described various natural chemicals our bodies manufacture — and how their effects on the brain relate to the experience of romantic love. Perhaps the most interesting is phenylethylamine, or PEA. Liebowitz theorized that PEA is responsible for the exhilaration and euphoria of falling in love, through its effect on other neurochemicals: increasing dopamine and norepinephrine; decreasing serotonin.
Dopamine works on brain “reward” systems , stimulating attention. It used to be considered a pleasure switch, but it turns out that dopamine is triggered by danger as well as by pleasant experience, and that the attention itself aroused by either… is motivating. The role of dopamine is demonstrated in Parkinson’s Disease, which shuts down its victims’ ability to pay attention to the world: treatment with a drug that increases brain levels of dopamine can restore attention. (Unfortunately there are also undesireable effects.)
Interesting research on the brain in love uses functional magenetic resonance imaging (fMRI), which measures cerebral blood flow. With this method, we can’t say dopamine “causes” a certain state of mind, but rather that the experience activates, or is associated with, increased activity in brain regions rich in dopamine. And indeed, typical features of romantic love are associated with them: ecstasy, intense energy, hyperactivity, sleeplessness, mood swings, emotional dependence, and craving.
Norepinephrine (also called noradrenaline), which is made by the body from dopamine, gears the body for fight or flight: raising heart rate; triggering the release of glucose from energy stores; increasing blood flow to skeletal muscle and the supply of oxygen to the brain. It’s also involved in reactions to stress in several brain regions — notably the amygdala. In the excitement of falling in love, it may well be norepinephrine that produces the sweaty palms, pounding heart, and butterflies in the stomach. But I have not found neuroimaging studies on this yet.
Serotonin regulates how well electrical nerve impulse signals get transmitted from one neuron to the next. Deficiency means depression, and more makes people happier. Many drugs owe a lot of their popularity to this effect, both the prescription versions — MAOIs and SSRIs like Prozac and Zoloft — and also recreational ones, including Ecstasy, and even mescaline, LSD and other psychedelics. However biological anthropoligist Dr. Helen Fisher, who studies romantic love, warns that antidepressant medication can impair the body’s physiological systems of romantic love.
When you drive up the neurotransmitter serotonin in the brain, you are highly likely to suppress the dopamine system, and my colleagues and I have clearly found that elevated activity in the dopamine system is linked to one’s romantic feeling. …I’ve gotten a good deal of mail from people who’ve said they were in a nice short or long romance or marriage with someone that was going perfectly well, and this person started taking SSRIs, and it not only killed their sex drive, but it also killed their feelings of intense romantic love for their partners.
Amphetamines’ effects are similar to PEA’s. Indeed, a PEA high is very like a speed trip: Your palms sweat. You’re giddy, excited, so happy you can’t sleep. Butterflies flutter in your stomach. You feel wonderful. Others notice how you positively glow. Your concentration is phenomenal. But on PEA, you typically don’t cram for exams. You can only concentrate on one thing — your beloved.
Although research now focuses downstream from PEA, it’s still behind the other three suspects. And I can’t help thinking in terms of PEA, as a shorthand for the neurochemicals of romantic love — because it shook me up so much when I first learned about it.
A brain chemical behind falling in love! The idea commanded popular attention, especially when Liebowitz mentioned the PEA in chocolate. Unfortunately, in the digestive tract PEA gets very quickly broken down by monoamine oxidase: you can’t get high from ingesting it, unless you also take a MAO inhibitor. People who have experimented with this testify it’s a great feeling, but difficult to manage, risking results like those from amphetamine abuse. One person said “I am quite certain that I incurred significant brain damage.” 
Liebowitz reported on a study at the National Institute of Mental Health in which subjects ate 200 g of Cadbury milk chocolate without raising the level of PEA excreted in their urine. The researchers concluded that diet contributed little PEA.  But the popular press reported that Liebowitz had propounded a “chocolate theory of love.”
PEA levels drop after two to five years in one relationship. The high is gone. It’s not anything you did wrong, it’s biology. When I learned this, my whole attitude toward romantic love changed.
For years I’d felt uneasy because I’d married Jesse without being in love with him. That wasn’t the way it was supposed to be. I even felt oddly guilty: had I betrayed myself, by not holding out for the Real Thing? Had I settled for second best? When we decided on an open marriage, I went hunting for that romantic high, trying to understand. I had fallen in love plenty of times before I married, but it never worked out. Now I was determined to get it right. Perhaps desperate even. How could I be true to myself, to that part of me that blossomed when I was in love?
And still I failed. Eventually I gave up looking, but I carried a sense of failure somewhere deep … until I read about PEA: It wasn’t my fault romantic passion didn’t last! The cultural script is a disaster: building a long-term relationship on the PEA high is insanity — is impossible. I no longer thought there’s something wrong with me, I thought our culture is obsessed with a chimera.
Many people, falling in love with a new partner, abandon the established one. PEA euphoria is addictive, and our whole culture is addicted.
When PEA fades, other neurochemicals have greater impact on the experience of relationship. As they do from the beginning, for those of us who marry for reasons other than being in love.
 Fisher and Thomson, 2007, 245-283.
 Choi, August 2, 2011.
 user shibireru, comment on thread “Too much Phenylethylamine (PEA)?”, on Bluelight Harm Reduction Forum and Research Portal, January 27, 2009.
 Liebowitz, 1983, 100.