What is the chemical for love

Blocking oxytocin disrupts the pair bonding that is here a surrogate for love, and makes the voles more restrained in their emotional expressions. Conversely, inducing an excess of oxytocin in other, non-monogamous vole species blunts their taste for sexual adventure. In humans, though, the effects are much less dramatic – a subtle change in the romantic preference for the familiar over the new. So oxytocin is far from proven to be essential to love.

Of course, even if we could identify such a substance, any message – chemical or otherwise – needs a recipient. So where is the letterbox of love in the brain? And how is the identity of the “chosen one” conveyed, given that no single molecule could possibly encode it?

When romantic love is examined with imaging of the brain, the areas that “light up” overlap with those supporting reward-seeking and goal-oriented behaviour. But that parts of our brains are set ablaze by one thing does not tell us much if they are just as excited by a very different, other thing. And the observed patterns of romantic love are not that different from those of maternal bonding, or even from the love of one's favourite football team. So we can only conclude that neuroscience is yet to explain this "head over heels" emotion in neural terms.

Do we simply need more experiments? Yes, is usually the scientist's answer, but this assumes love is simple enough to be captured by a mechanistic description. Each reproductive decision can be neither simple nor uniform, for we cannot be allowed to be guided by any single characteristic, let alone the same one. Universally attractive though tallness might be, if biology allowed us to select on height alone we would all have gigantism by now. And if the decisions have to be complex, so must the neural apparatus that makes them possible.

While this explains why romantic attraction must be complex, it doesn't explain why it can feel so instinctual and spontaneous – unlike the deliberative mode we reserve for our most important decisions. Wouldn't a cool, detached rationality be better? To see why it would not, consider what explicit reasoning is there in the first place. Evolving later than our instincts, we need rationality only to detach ourselves from the grounds for a decision so that others can record, understand and apply it independently of us.

But there is no need for anyone else to understand the grounds for our love, indeed the last thing we want to do is provide others with a recipe to steal our object of desire. Equally, in ceding control to recorded cultural practice, evolution would place too much "trust" in a capacity – collective rationality – that is, in evolutionary terms, far too young.

It is also a mistake to think of instinct as simple, and inferior to careful deliberation. That it is tacit makes it potentially more sophisticated than rational analysis, for it brings into play a wider array of factors than we could ever hold simultaneously in our conscious minds. The truth of this stares us in the face: think how much better we are at recognising a face compared with describing it. Why should the recognition of love be any different?

Ultimately, if the neural mechanisms of love were simple, you should be able to induce it with an injection, to extinguish it with a scalpel while leaving everything else intact. The cold, hard logic of evolutionary biology makes this impossible. Were love not complicated, we would never have evolved in the first place.

That said, love – like all our thoughts, emotions and behaviours – rests on physical processes in the brain, a very complex interplay of them. But to say that love is "just" brain chemistry is like saying Romeo and Juliet is “just” words – it misses the point. Like art, love is more than the sum of its parts.

So those of us lucky to experience its chaos should let ourselves be carried by the waves. And if we end up wrecked on the surf-hidden rocks, we can draw comfort from knowing reason would have got us no further.

This article is part of Life's Big Questions, a new series by The Conversation that is being co-published with BBC Future. It seeks to answer our readers' nagging questions about life, love, death and the Universe. We work with professional researchers who have dedicated their lives to uncovering new perspectives on the questions that shape our lives. If you have a question you would like to be answered, please email either send us a message on Facebook or Twitter or email 

Parashkev Nachev is a professor of neurology at University College London.

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Passionate love has proven biochemical bases. This is the kind of love experienced with a romantic partner, one that involves sexual desire usually. There are many studies conducted on the brain when passionate love is involved. Researchers scanned people’s brains in an fMRI scanner while they looked at photographs of either strangers or people they were in love with. The results showed interesting things about brain activities in love.

This is a transcript from the video series Understanding the Mysteries of Human Behavior. Watch it now, on Wondrium.

Dopamine and Passionate Love

When the participants of the fMRI study looked at pictures of those they were in love with, the caudate nucleus was activated in the brain. This area of the brain has receptors for a neurotransmitter called dopamine. Dopamine causes feelings of exhilaration, gives people extra energy, focuses their attention, and makes them want rewards.

These are all experienced when someone is in love as well.

Learn more about what makes people happy.

Phenylethylamine or PEA

Phenylethylamine or PEA is the second neurotransmitter involved in passionate love. It is a chemical associated with amphetamines, and its effects on people’s moods and energy are similar to those of various stimulants.

This is why people in love feel energized, upbeat, and optimistic. PEA and dopamine together give enough energy and reason to a person to stay up all night and talk to the person they are in love with.

When a romantic relationship fails, the emotional crash and the occasional depression are similar to what people feel when they stop taking amphetamines or other stimulants. Although the psychological pain of losing an important relationship is a part of feeling down after a breakup, the lack of chemicals that used to be produced due to love is a major part.

Oxytocin and Love

The third chemical in both companionate and passionate love is oxytocin. Unlike PEA and dopamine, oxytocin is released in close non-romantic relationships as well. Family relationships, friendships, and other types of love involve release of oxytocin as well.

Oxytocin is the hormone responsible for the close psychological connection a person feels with their loved ones, whether it is a romantic partner or a parent. Hugging a long-term partner or a child, a mother’s nursing an infant, and orgasm, all release oxytocin. It leads to the feeling of social connection and being bonded with the other person, regardless of the type of relationship.

Lovers and parents with children show similar activities that make them feel good: long eye contact, touches, being physically close to the other person, and hugging. Even baby talk is common in many romantic relationships.

Even if oxytocin enters the body from an external source, it makes people feel closer to other people and trust them more. It makes people more empathetic and helps them understand other people better.

Obsession and Compulsion in Passionate Love

When a person is in love, they show patterns similar to those in patients of obsessive-compulsive disorder (OCD). They cannot stop thinking about the other person—uncontrollable thoughts, feelings, and ideas. As a result, they decide to do certain things (compulsion), like being with the other person.

Scientists believe that people with OCD have problems with serotonin, another important neurotransmitter that matters in the regulation of mood, sleep, learning, and other processes that involve the brain.

Learn more about how much men and women really differ.

Serotonin, Love, and OCD

In a study in Italy, three groups of people were tested for serotonin to see if those in love show similar serotonin patterns to patients with OCD: people who had fallen in love in the last six months and reported that they were obsessed about the loved one; people who had been clinically diagnosed with OCD; and people who were neither in love nor diagnosed with OCD.

The blood test results confirmed the hypothesis: those passionately in love and those with OCD showed similar serotonin patterns, i.e., 40% less than the group that was neither in love nor had OCD.

Learn more about what makes relationships succeed or fail.

Love through Time

The early passion in love will eventually fade away. The love, wanting, respect, and commitment can last forever, but the high passion will disappear in a long-term relationship. After 20 years of marriage, people are still in love, but not passionately anymore.

Physiologically, oxytocin takes over eventually and becomes the core of the relationship, while PEA and dopamine lower and gain a more normal level.

In terms of evolution, the excitement needs to stay around long enough for the couple to reproduce. After that, evolution no longer cares for the parents, but the children must find a partner and reproduce again. Thus, passionate love declines, especially after having children, but the relationship can survive and strive without it, too.

Common Questions about Passionate Love

Q: What is PEA?

Phenylethylamine or PEA is a neurotransmitter involved in passionate love. PEA is a chemical that is related to amphetamines and affects people’s moods and energy, like various stimulants.

Q: Is oxytocin released only in romantic relationships?

No, oxytocin is not limited to passionate love. Oxytocin is a hormone that promotes a feeling of social connection and being bonded with another person. It is released naturally when one hugs a long-term partner or their children. It is also released when a mother nurses her infant, and also during orgasm.

Q: What chemicals are involved in love?

Dopamine, oxytocin, serotonin, and Phenylethylamine or PEA are among the essential chemical components of passionate love.

Q: Does love disappear in long-term relationships?

Passionate love does not disappear after some years. Instead, it gets less exciting, and mainly hormones and chemicals related to trust and loving keep the relationship happy and healthy.

Keep ReadingHow Do The Brains of Men and Women Differ?What Makes Us Human—Identifying a Universal Set of EmotionsWhat Makes People Happy? Genetics vs. Circumstances