It's the thorny side of love that makes it so addictive

For all the dizzy highs of romantic love, there are corresponding lows of heart-break, betrayal and the anguish of unrequited love

With its origins in Roman Catholic martyrology, February 14 has become a global celebration of romantic love. Many of our most beautiful achievements have been inspired by it. But this exalted muse, clothed in the cloak of complex human emotion, has a dark-side too.

Like sadness, anger and anxiety, romantic love is capable of deviating beyond the boundaries we call healthy, the boundaries we call legal. Occasionally, romantic love mutates, leaving dysfunction, distress and sometimes even death in its wake.

In its most harmless incarnation, romantic love has been equated with mild-to-moderate manic symptoms (hypomania). A study by a Swiss research team, published in 2007 in the Journal of Adolescent Health, concluded that early-stage romantic love in teenagers was comparable to hypomania. So even in its most innocuous form, romantic love resembles a mild mental health problem. What then, when romantic love goes awry?

One of the first psychologists to give extensive research attention to "problem love" was Dorothy Tenov, a psychology professor and author of Love and Limerence: The Experience of Being in Love. Professor Tenov coined the term "Limerence" to describe an involuntary and extremely powerful emotional attachment towards another person. This attachment is obsessive in nature, and the person experiencing it is beset by repetitive and intrusive thoughts concerning the object of their affection.

There is also a strong desire that their obsessively amorous feelings be reciprocated. In extreme cases the obsessions are all consuming, akin to drug addiction. This can mean previous interests are abandoned, and almost every waking moment is devoted to thoughts and fantasies about the love interest, or to use Ms Tenov's terms, the limerent object.

Romantic love clearly involves cognitive, emotional, physiological and behavioural components all feeding into each other, any of which can become excessive and problematic. At the physiological level, people may experience elevated heart rates and complain of appetite loss (anorexia) and sleeplessness (insomnia); at the behavioural level, you might see the full spectrum of stalking behaviours, from "coincidence engineering", to elaborate, CIA-style surveillance.

A further ugly twist in the tale of romantic love is its occasional mutation and decent into pathological jealousy. Psychologists generally study, and treat, pathological jealousy in the context of romantic relationships, earning it the nickname "love's executioner". The Oxford English Dictionary defines jealousy as: "Feeling or showing resentment towards a person one thinks of as a rival." This rival (real or imagined) is often viewed as a threat to one's cherished romantic relationship.

This pathological jealousy can be viewed as good love gone bad: an explosive blend of anger and anxiety. In extreme cases it can escalate to acts of abuse and violence. Gerhard Falk, a historian and sociologist with an extensive, and rather morbid knowledge of US crime statistics, lists jealousy as the fourth most common motive for murder, implicated in 10.8 per cent of all homicides.

When looking for traits in a marriage partner, few people tick the boxes "irrational", "delusional" and "obsessive". But these are the very traits displayed by the love-struck. Perhaps this irrationality is what we find endearing; the idea that if a better deal ever did come along, this person is just "crazy" enough to pass it up and stick around. At least, this is the basic explanation of infatuation offered by Robert Frank, professor of economics at Cornell University.

Sadly, though, love appears to be losing its longevity, especially if rising divorce rates are an indication. So, for all the dizzy highs of romantic love, there are the corresponding lows of heart-break, betrayal and the anguish of unrequited love.

Would a pharmaceutical company marketing a pill capable of preventing the onset of romantic love make billions? Or, are we happy to anticipate pain as the natural occasional accompaniment of our pleasure? An idea eloquently expressed by Saadi of Shiraz, the 13th century Persian poet, who suggests: "The company of the rose would be sweet if there were no pain from thorns".

Justin Thomas is an assistant psychology professor at Zayed University in Abu Dhabi

On Twitter: @jaytee156