The Chemistry of Love

Lucy Bell-Young

by Lucy Bell-Young

14th February 2018

In honour of Valentine’s Day, we thought we would take a look at the chemistry behind the culprit of this love-hate holiday: love. From that first high school crush to the marital vow, we’re looking into what makes us giddy and what keeps us obsessed.

It’s that time of year again: Valentine’s Day. Whether you’re celebrating it with your partner, your friends, or your favourite 12” pizza, there’s no doubt that a whole lotta love is going to be shared today. So what is love exactly?

What is Love?

Aside from the starry eyes, the sweaty palms, and the flutter of butterflies filling your stomach, love is a chemical state of mind that involves the same chemical processes that happen during a drug addiction.

Love usually happens in 3 stages, each of which has its own distinct chemistry:

  1. Lust: this is the initial stage of attraction, and is believed to have been developed in order to fulfil sexual mating and procreation. In this category’s play of chemistry, oestrogen and testosterone take centre stage.
  2. Romantic Passion: this is the most intense stage of love where we tend to think irrationally and idealise our object of passion. This is thanks to the brain’s favourite trio: norepinephrine, dopamine and phenylethylamine, which we’ll get into shortly.
  3. Attachment & Commitment: this is the final stage of a relationship, where the passion may have fizzled out in favour of an overwhelming attachment to your significant other. This is thought to have developed in order to form mother-infant bonding, and all comes down to oxytocin, antidiuretic hormones and endorphins.

In terms of evolution, there is only one goal that the experience of love has: the continuation of our species. While this is a rather sterile take on the world’s strongest emotion, it is why the chemicals released in our brain are so intense and pleasure-filled. Let’s take a look at why we become weak-at-the-knees.

Love heart shaped lights glowing amber in the dark

Love and the Brain

The initial spark of falling in love – the racing heart, the sleepless nights – is caused by three neurochemicals: norepinephrine, dopamine and phenylethylamine.

When these chemicals combine, it causes elevated levels of pleasure, energy and focussed attention. As the anthropologist Helen Fisher said, this “cocktail of love rapture” explains why an overwhelming preoccupation with our object of passion is engraved into our biology.


Also known as noradrenaline, norepinephrine is a hormone and neurotransmitter that stimulates the production of adrenaline. This hormone is responsible for that racing heart, the sweaty palms, the flushed cheeks, and even the loss of appetite we experience when we’re falling in love.

Norepinephrine is released from nerve cells in our brain in the form of noradrenergic neurons. These form the norepinephrine system which, when activated, affects large areas of our brain.  Norepinephrine exerts its effects by binding to target cells and activating its adrenergic receptors. Main target cells include the spinal cord, thalamus and neocortex.

High levels of norepinephrine in the brain leads to an increased experience of joy, as well as a loss of appetite.


Another neurotransmitter that plays a huge part in the experience of love is dopamine, a neurochemical that is released when we feel good. Activities such as eating, exercising, or watching your favourite movie stimulate the production of dopamine in our brains.

Dopamine has significant effects on brain processes that control our emotional responses and ability to express pleasure. Therefore, dopamine is what makes those in the grips of passion more talkative and excitable than usual. Sociability in general is closely tied to dopamine neurons. In fact, those with social anxiety have often been found to have low dopamine levels.

Dopamine is the precursor to norepinephrine. This means that without dopamine, the physical effects of norepinephrine wouldn’t happen.

As a neurotransmitter, dopamine activates as many as 5 different receptors in the brain that are associated with the pleasure system. This creates elevated feelings of enjoyment. It also reinforces feelings of motivation, which in turn encourage a person to be more proactive.

Phenylethylamine (PEA)

Phenylethylamine is a natural stimulant that behaves like an amphetamine. Known as the molecule of love, it is often associated with the butterflies we feel when we’re around our crush.

It is our first attraction to someone that causes our brain to release high levels of PEA. This results in the dizzying feelings associated with romantic love.

Most familiarly known as the feel-good chemical in chocolate, PEA also stimulates the production of endorphins and dopamine. Rather than a neurotransmitter, phenylethylamine acts as a neuromodulator by increasing extracellular levels of dopamine and modulating noradrenergic transmission.

Therefore, PEA helps to enhance the actions of the two previous neurochemicals. This is why large quantities of PEA lead to increased physical and emotional energy.

When these three neurochemicals come together, they comprise the chemistry of love. They are also the reason that new love – romantic passion – makes us feel emphatic and energised. But if the chemicals released in our brain during romantic passion are similar to those released during a drug addiction, is love, by extension, a sort of drug?

Photo of a transparent skull model in a gallery

Can Love Be Addictive?

The effects caused by dopamine, norepinephrine and phenylethylamine can be likened to an amphetamine-like euphoria. Over time, the body builds up a tolerance to this “love high” in the way it would to any addictive substance. Love junkies go through relationship after relationship in order to get their fix, but is there any scientific foundation supporting the addictive nature of love?

The answer lies in the mesolimbic dopamine system, a dopaminergic pathway in our brains that subconsciously rewards us for doing something with an evolutionary benefit, like eating or having sex. This area of the brain is associated with motivation, reward and craving.  Two major areas the mesolimbic dopamine system are the:

  • Ventral Tegmental Area (VTA)
  • Nucleus Accumbens

One way addiction influences our brain is by hijacking this mammalian reward and motivation system. Studies using Functional Magnetic Resonance Imaging (fMRI) technology to record the brains of people in love have shown increased activity in this reward and motivation system of the brain when its subjects were shown photos of their significant other. The same activation in this area of the brain has also been recorded when people take cocaine.

The same studies have also recorded the brains of those who had been rejected, but were still in love with their exes. When shown photos of their lost love, fMRI technology revealed elevated activity in the VTA and nucleus accumbens. This type of activity also shares multiple neural correlates with the brain of cocaine addicts craving a fix.

Therefore, at the level of brain chemistry, love can be an addictive substance that can even cause us to obsess over our object of passion in the same way an addict would over their drug.

Love and Obsession

The obsessive preoccupation many people experience when they become infatuated with someone can be put down to levels of serotonin in their brain.

Serotonin is a neurotransmitter that is biochemically derived from tryptophan, an amino acid, and most commonly known as the contributor towards feelings of well-being and happiness. The level of serotonin in our brain has many impacts on the functions of our body, such as mood, aggression, memory, appetite and sleep.

The deeper structures of the brain and the front part of brain often use serotonin to communicate. Depleted levels of serotonin can disrupt this communication, resulting in hyper-awareness, feeling on-edge, obsessive thoughts and compulsive behaviour. Because serotonin plays a vital role in so many bodily functions, having an imbalance of it can affect us on many different levels.

Low serotonin levels are often present in those who suffer from thing like OCD, anxiety, and even those who are love-struck. In the early stages of romantic passion, levels of cortisol, our stress hormone, increase in order to help us cope with the rush. As cortisol increases, serotonin decreases. According to Richard Schwartz, this is why romantic passion and infatuation are punctuated by “maddeningly preoccupying thoughts” and obsessive-compulsive behaviours.

Serotonin, then, is the culprit behind that high school crush we just couldn’t shake; the inability to think of anything but your new infatuation; even the new, obsessive phenomena of social media ‘stalking.’

A man stood outside at night with a bouquet of flowers


Past a certain point, the romantic passion may have faded and you may no longer get butterflies. But all of this is replaced with a new kind of love: attachment, which is the final stage. This, too, has its own personal chemistry.

Oxytocin is a powerful hormone that is released when we have sex. It also has a key role in maternal-infant bonding and milk release. This is why, when it is released during sex, it causes humans to form an emotional bond between partners. This is also why the more you have sex with the same person, the more likely you are to develop a strong emotional bond and relationship with them. Therefore, while oxytocin is a major factor in the non-committal first stage of lust, it also paves the essential pathway to attachment.

Endorphins are also important when it comes to the chemistry behind long-term relationships. Endorphins are your body’s natural painkillers, and promote feelings of well-being, security and contentedness. In fact, the effect of endorphins on our brain chemistry has been likened to a drug-like dependency, and explains why humans become attached and even addicted.

Why Does the Lust Fade?

When relationships have stood the test of time and become long-term, it is often said that the initial passion and spark is lost. Rather than this being a symptom of falling out of love with each other, it is more a result of an antidiuretic hormone called vasopressin.

Vasopressin is closely associated with the formation of long-term relationships because it works in tandem with oxytocin. The side-effect of this is that the dopamine and norepinephrine pathways actually become interfered with and disrupted. This is why, scientifically speaking, the passionate spark fades as attachment grows.

A photo showing a close-up of two people holding hands in a meadow

Like most things that surround us, love has a complex chemistry underpinning its sugary sweet surface. So the next time you get a case of the butterflies, or find yourself wondering where that passionate spark has gone, just remember that it’s all in your head – literally!


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