From lust to attachment: The neurobiology of love
What is love? As Dr. Helen Fisher, a prominent anthropologist, once said, "Until recently, we regarded love as supernatural." However, it is more of a drive than anything else, involving a complex interaction of brain chemicals.
Many can relate to what Fisher said, as love can change everything and feel somewhat magical. So, how does the brain respond to love, and how do these responses evolve? While all couples have their own unique love story, scientists have begun to uncover that feeling and experience from a neurobiological standpoint.
Here's how to better understand the roller coaster created by love and the brain. Buckle up.
Introduction to the three stages: How does romantic love progress?
As stated by Dr. Helen Fisher, romantic love progresses in three stages: lust, attraction, and attachment. Varying hormones increase during these phases, encouraging people to transition from feelings of sexual desire to lifelong partnerships 
During feelings of romantic love, your brain enters a state that drives emotions and activates the reward circuit in the brain.
Early-stage, intense love feels good, and your reward system responds, motivating you to win your preferred partner. At this point, you may feel excited as hormone and brain chemical levels spike. For example, dopamine is a prominent love chemical in brain research. Brain scans show that when romantic lovers look at photos of their lovers, brain regions related to reward, motivation, and emotion regulation are activated .
But that's just the beginning. Brain chemicals are along for the ride from that initial spark to a couple's 20th wedding anniversary.
Stage 1: Why do we experience feelings of lust
Lust. It's where it all starts. This stage precedes the formation of an emotional connection, with reproductive hormones creating feelings of desire.
When you feel lust toward someone, they may be unaware. Without action, they may forever remain thoughts in your mind. Those who act on lust can develop a loving relationship, but that takes time and involves more chemical interactions.
Feelings of lust, attraction, and long-term love involve brain chemicals, some of which overlap between stages. The progressive nature of love first involves reproductive hormones when experiencing lust, primarily driven by evolution. In men, testosterone fuels this stage, while estrogen is more predominant in women. When feeling lust, the goal is to seek sexual gratification rather than build a relationship — but that can quickly change and often does .
Stage 2: How does it turn to attraction?
Attraction is linked to lust but is distinct because it involves chemicals that control "reward" behaviors.
Dopamine is one love chemical in the brain that influences the euphoric attraction stage. When you are attracted to someone, high dopamine levels are released, and the pleasure center of your brain activates. Your brain processes feelings experienced during the attraction stage as a reward .
Reinforcement strengthens this distinct yet intertwined stage, allowing couples to develop what many refer to as the "honeymoon" phase. This phase helps explain a relationship's first weeks and months when everything is exhilarating. The romantic photograph study discussed above shows activation of the brain's reward center, with these effects lasting between 7.4 and 28.8 months.
As attraction fades, attachment takes over.
How do men and women respond to serotonin during attraction?
When diving deeper into the science behind love, another love chemical in the brain plays a crucial role — serotonin. The chemical regulates mood and sleep. However, it also influences the initial love stage of attraction differently for men and women.
Interestingly, while both men and women experience changes in serotonin levels, this love chemical in the brain responds differently depending on your sex. Research on love and the brain shows that women have higher serotonin levels when in love, whereas men have lower levels. So, while serotonin plays a key role in romantic love, the effects are the opposite between men and women. Currently, the mechanism of action related to dropping serotonin levels in men is unclear 
Even though serotonin levels decrease during the attraction phase, sex can cause levels to increase once again.
Stage 3: What brain chemicals promote bonding and long-term love?
Following lust and attraction, the science behind love transitions toward bonding mechanisms and the attachment phase. Long-term love is linked to oxytocin, the bonding chemical, and vasopressin, another love chemical in the brain that promotes pair bonding. Again, differences are seen across men and women, as females are more sensitive to oxytocin than men, who are more sensitive to vasopressin. Oxytocin is also pivotal concerning early parent-infant bonding, which is why it's been coined the love hormone .
Animal studies showed that injecting oxytocin and vasopressin promotes pair bonding . More specifically, when vasopressin levels increased, this initiated monogamy, bonding, and a desire to protect their partners.
Love and the brain: final thoughts
Forming a lasting bond with someone you love is a multi-stage process involving a spectrum of brain chemicals. While the heart is a symbol of love, the verdict is in. Your brain is making all the big moves, and depending on how your love progresses, your heart often pays the consequences. For those lucky ones that share a passionate, loving relationship for the entirety of their adult lives, they have their brains to thank — well, their brains and their partners, of course.
The science behind love is rooted in the brain chemicals that flood it. It is a wild ride, and your brain is always in the driver's seat.
Wu, Katherine. (2017). Love, Actually: The science behind lust, attraction, and companionship. Available from: https://sitn.hms.harvard.edu/flash/2017/love-actually-science-behind-lust-attraction-companionship/
Song, H. et al. (2015). Love-related changes in the brain: a resting-state functional magnetic resonance imaging study. Frontiers in human neuroscience, 9, 71.
Seshadri K. G. (2016). The neuroendocrinology of love. Indian journal of endocrinology and metabolism, 20(4), 558–563.
Langeslag, S. J. et al. (2016). Regulation of Romantic Love Feelings: Preconceptions, Strategies, and Feasibility. PloS one, 11(8).
Langeslag, S. J. E. (in press). Is the serotonergic system altered in romantic love? A literature review and research suggestions. In E. Cuyler & M. Ackhart (Eds.). Psychology of Relationships. Hauppauge: Nova Science Publishers.
Langeslag, S et al. (2012). Blood Levels of Serotonin Are Differentially Affected by Romantic Love in Men and Women. Journal of Psychophysiology. 26. 92-98.
Scatliffe, N. et al. (2019). Oxytocin and early parent-infant interactions: A systematic review. International journal of nursing sciences, 6(4), 445–453.
Carter, C. S. et al. (2018). The Monogamy Paradox: What Do Love and Sex Have to Do With It? Frontiers in ecology and evolution, 6, 202.