Nataliia Bohdanova

Scientists have long established that love is an emotional state rooted in the production of specific “happiness hormones.”

Love triggers a cascade of hormones, each contributing to distinct phases of the emotional experience. According to Robert Sternberg’s triangular theory of love, relationships evolve over time, progressing through three key stages: intimacy, passion, and commitment. Similarly, psychologist Carlos García identifies three phases of romantic relationships: infatuation (being in love), passionate love, and companionate love. The first stage, infatuation, typically lasts about six months and is marked by high levels of passion and emotional intensity. The second stage, passionate love, can span several years, during which the initial euphoria gives way to calmness, and stress levels decrease due to cortisol normalization.

This process of transitioning from initial euphoria to emotional calmness and reduced stress levels is influenced by the action of oxytocin and vasopressin — hormones that promote long-term bonding, emotional security, and a sense of trust between partners.

Sexual Attraction and Falling in Love: Testosterone, Estrogen, Norepinephrine, Serotonin and Dopamine

At this stage, hormones play a key role:

• Testosterone awakens sexual desire and enhances physical attraction in both men and women.
• Estrogen enhances sensuality and attractiveness while playing a direct role in fertility.
• Norepinephrine increases heart rate, causes sweaty palms, and creates the famous “butterflies in the stomach” sensation.

This phase is deeply rooted in basic instincts, including reproduction and the search for an ideal partner.

Dopamine is the first hormone activated during the onset of romantic love. Its production is driven by the “goal-achievement” effect, which occurs when the brain perceives that the desired goal — romantic attention or connection — is within reach. This motivates the person to pursue it. Dopamine generates feelings of euphoria and intense pleasure, but its effects are short-lived. The continuation of a relationship depends on whether the partner’s behavior meets expectations. If expectations are fulfilled, dopamine production persists, reinforcing the bond. If not, dopamine levels drop, reducing interest.

Inlove, dopamine contributes to the onset of infatuation in the initial stage, but its subsequent decline often leads to feelings of depression and disappointment.

Passionate Love. The hormones Adrenaline and Cortisol

Adrenaline plays a key role in intensifying passion and is often referred to as a “chemical amplifier of love.” Stressful situations trigger its release into the bloodstream, leading to heightened excitement and readiness. In those who are in love, adrenaline levels rise significantly, enhancing focus and motivation.

SSerotonin regulates mood and emotional stability, creating feelings of satisfaction and happiness. During romantic infatuation, serotonin levels drop, leading to obsessive tendencies and an intense focus on the loved one.

The feeling of satisfaction after orgasm is largely regulated by serotonin. This hormone affects mood and emotional flexibility, forming a delicate balance with dopamine. When dopamine levels surge, as at the start of a romantic relationship, serotonin levels drop, leading to an intense focus on the object of affection. The lover becomes deeply preoccupied with their partner, overlooking flaws and idealizing them. However, after about a year, biochemistry begins to shift, and serotonin levels return to normal, diminishing the intensity of passion. The rise in serotonin brings contentment but reduces motivation. This is why the intensity of early romance fades, and its preservation requires conscious effort.

Cortisol enhances focus on the object of affection. A person in love experiences obsessive thoughts about their partner, which is linked to cortisol’s influence on cognitive processes and heightened attention to “significant” stimuli.

The elevated level of cortisol explains why people in love often experience intense mood swings — from euphoria to anxiety. This is further exacerbated by a drop in serotonin levels, which makes emotions even more intense.

Attachment and Friendly Love

Inthe early 2000s, scientific research revealed the remarkable devotion of praIn theirie voles, a species known for their extraordinary lifelong bonds. After their first mating, these voles form pairs that remain together for life. They work as a team to gather food, raise their offspring, and display unwavering affection. In contrast, montane voles exhibit entirely different behavior, avoiding long-term relationships and adhering to a polygamous lifestyle. This behavioral difference is attributed to the varying density of oxytocin and vasopressin receptors in specific regions of their brains.

The primary physiological function of vasopressin is to regulate fluid retention in the body by increasing water reabsorption in the renal tubules. However, studies have unveiled its critical role in fostering attachment between individuals of the opposite sex.

Oxytocin and vasopressin receptors in the brain — protein molecules that bind to these hormones — trigger changes in neuronal activity. In monogamous prairie voles, these receptors are found in abundance in brain regions linked to the reward system, such as the nucleus accumbens (the pleasure center), the pre-limbic cortex, and the lateral amygdala. In polygamous voles, the concentration of these receptors in these areas is significantly lower, which likely explains their distinct behavioral tendencies (Erich Fromm, 1965).

The Impact of Oxytocin on Women’s Attachment

Initially, oxytocin was primarily used in medicine to induce labor, as it was thought to function solely as a hormone triggering uterine contractions and initiating the childbirth process. It also stimulates the mammary glands to release milk. However, subsequent research revealed that oxytocin affects more than just physiological processes — it plays a critical role in a mother’s emotional state. This hormone fosters a deep bond between a mother and her child, motivating her to care for and protect her baby.

Moreover, a woman’s level of oxytocin can indicate the strength of her emotional attachment to her partner and her readiness for close relationships. A study conducted in England during a wedding examined blood samples from the groom, the bride, and their relatives right before the couple exchanged vows. The highest levels of oxytocin were found in the bride, followed by her mother, and then the groom’s father, underscoring the hormone’s connection to emotional closeness and attachment.

The Role of Vasopressin in Male Attachment

Larry Young, a neurobiologist at Emory University, discusses experiments on different species of mice in his book ‘The Chemistry of Love.’ These studies explore how hormonal differences influence monogamous and polygamous behaviors.

Male gray voles have very few vasopressin receptors. However, when genes from prairie voles are introduced into their genome, these gray voles develop a tendency toward monogamy. The formation of pair bonds in prairie voles involves two types of receptors — type one and type two. Research led by Brendan Gingrich at Emory University demonstrated that activating the type two receptor leads to the instant formation of a pair bond, even before mating occurs. Conversely, blocking this receptor prevents the formation of a bond. When only the type one receptor is selectively activated, the levels of which typically rise in the brain after pair bonding, monogamous voles show no inclination toward forming an attachment with the opposite sex.

Although both men and women produce oxytocin and vasopressin, it is generally believed that attachment in women is predominantly regulated by oxytocin, whereas in men, vasopressin plays the leading role. Among couples who have spent many years together, the number of receptors for these hormones likely increases. At the same time, dopamine levels decrease, which explains why people often feel that love and passion have faded over time.

CONCLUSION

Dopamine triggers feelings of euphoria and pleasure from interacting with a loved one, norepinephrine speeds up the heartbeat and creates the sensation of “butterflies in the stomach,” while a drop in serotonin levels leads to obsessive thoughts about the partner. At the same time, cortisol, the “stress hormone,” increases, explaining the emotional instability and intense experiences during the early stages of love. This hormone helps focus attention on the object of affection, strengthening the bond.

As the relationship develops, cortisol levels gradually normalize, and attachment hormones — oxytocin and vasopressin — take center stage. They reinforce the emotional connection between partners, promoting trust and stability. Together with endorphins, which induce feelings of comfort and satisfaction, these substances help form long-term relationships.

Thus, love is not only a vivid emotional experience but also a complex process within the body. Hormones and neurotransmitters, from testosterone to oxytocin, facilitate a smooth transition from passion to deep attachment, making love both a biological and emotional phenomenon.