If this Ancient Egyptian poem is any guide, lovesickness has been with us for more than 3,000 years. But psychiatrists may be unintentionally “curing” us of that experience and other aspects of romantic love with modern antidepressant medications.

So argue the anthropologist Helen Fisher, and the psychiatrist James Thomson Jr. Their case, sketched out in Fisher’s recent book, Why We Love (Henry Holt, £13.22), centres on how certain antidepressants could be blocking chemical pathways in the brain that were paved by evolution to help us meet and keep mates.

The drugs, selective serotonin reuptake inhibitors (SSRIs), which include Prozac, Paxil and Zoloft, already come with warnings that they can suppress the libido and interfere with sexual functioning. But Fisher and Thomson argue that the problem may cut deeper into romantic bonds. “People in the medical community have known about the sexual side effects of these antidepressants but they have treated these as almost a secondary, minor issue — an annoyance. What I’m suggesting is that SSRIs have a major impact on three distinct but related brain systems we have evolved for the sex drive, romantic love and attachment,” Fisher says. “People need to be aware that these three brain systems interact in biological ways. You can jeopardise your ability to choose a mate appropriately, you can jeopardise your ability to fall in love and you can jeopardise your ability to feel attachment.”

As Thomson, a staff psychiatrist at the University of Virginia, explains: “The central nervous system is conservative, using the same neurotransmitters for multiple functions. That is why it is impossible not to have drugs without side effects. You correct one system, you imbalance the other — but that imbalance may not necessarily be conscious. Just because you have no consciously experienced sexual side effect does not mean that there aren’t any.”

SSRIs raise serotonin levels in the brain by slowing their removal. Fisher and Thomson assert that the love and lust of romance are centred on the neurotransmitter dopamine, and possibly norepinephrine, which have a negative relationship with serotonin. Dopamine, Fisher also notes, is associated with many qualities shared by both clinically diagnosed compulsions and anxiety disorders and with the heights of romantic love — hyper focusing, obsession, extreme motivation and a quest for novelty. Fisher and other researchers conducted an experiment in which the brains of people in the throes of early romantic love were scanned while they viewed photographs of their beloved and a more neutral acquaintance.

By tracking blood flows within the brain, the MRI scanner showed pronounced activity in two areas of the brain when the lover’s photograph was viewed. Both of these brain regions are associated with dopamine and powerful primitive reward systems.

If by raising serotonin levels dopamine and norepinephrine levels get hammered, romantic love would logically be threatened, they say. Indeed, often people are put on therapies in the aftermath of failed marriages and relationships. This is a positive response to what can be the dangerous effects of romantic depression: stalking, harbouring suicidal urges and withdrawing. But these regimens often linger long past the critical initial period, Fisher says. When people should be seeking new lovers, they may be unknowingly hindered by their elevated serotonin levels. Maryanne Fisher, a psychologist at York University in Toronto (no relation to Helen), reports the first evidence of “courtship blunting”. In a small study she conducted, women taking the drugs were asked to rate the attractiveness of men’s faces in photos. The women on this class of antidepressants rated the men more negatively and glanced over the photos at a quicker rate.

Serotonin enhancers can also dampen the sex drive of men and even their ability to ejaculate. These men naturally shy away from bedding women, leading to increased loneliness, setting up a vicious cycle of depression. Also, without frequent orgasms, men and women don’t have the flood of oxytocin and vasopressin that promote relationship bonding. Men might enjoy a woman’s company, but never fall head over heels for her. Semen may also be critical in retaining a woman’s interest, as recent studies indicate that men may alter women’s emotional states through chemicals transmitted through semen.

Helen Fisher, now at the anthropology department at Rutgers University, in New Jersey, but formerly of the American Museum of Natural History, in New York, writes that female orgasms might exist in part to test the time and effort partners are willing to devote to pleasing them, an important assessment for a mate during pregnancy and the critical child-rearing years. But women who are drugged are less sexual and thus “jeopardise their ability to assess the emotional commitment of a partner”. And besides not listening for important signals, people on the drugs — by being less sexual — are not sending out the right ones either: their seeming lack of desire signals a lack of love. They might even think their partner isn’t inspiring them and that they should look elsewhere, Fisher notes.

Thomson has seen these effects in his private practice and work at the University of Virginia. “People have been telling us this for years but we haven’t been paying attention,” he says. “I know I wasn’t. Now I think we need to be worried that we are not caring for patients at a deeper level, for their romantic relationships and potential romantic relationships.

“One guy on SSRIs would look at a beautiful woman and recognise that intellectually, but he said there was ‘no oomph’. He described being on the drugs as if the lenses in his glasses somehow had been changed. He wanted off the drugs. Even if he couldn’t chase women because he was a married man, he still wanted to enjoy looking.”

His sex life with his wife was also adversely affected, Thomson says. The patient, in his early fifties, had a good and stable marriage, several kids but had a very stressful job, a physical illness, and recurrent depressions “probably precipitated by his job and old family conflicts,” Thomson says.

Thomson also worries that some women could suffer a “double whammy” where antidepressants hinder their natural judgment to leave a bad relationship and also blunt their ability to spot healthy, desirable new mates. Indeed, he recalls that one patient wasn’t healthily distressed when an abusive ex-boyfriend with a history of stalking showed up at her door.

But it wasn’t individual case histories that brought Thomson’s worries into the mainstream. He and Helen Fisher connected through meetings of the Human Behaviour and Evolution Society, which Maryanne Fisher also attended. For several years Thomson buttonholed researchers to warn them that the growing popularity of SSRIs could be skewing their data, because the drugs could be altering the evolutionary behavioural adaptations in mating.

“The brain is like any other piece of tissue shaped by Darwinian natural and sexual selection. It was made and honed to solve reproductive problems faced by our ancestors over aeons of evolutionary history,” Thomson says. “And natural selection operates particularly fiercely in mating and mate selection. It’s an extraordinary system and we’re tinkering with it more than we know.”

Several academic researchers now say that they are taking Thomson and Fisher’s warnings seriously enough to begin screening volunteer subjects for SSRI use. How, or if, the Fisher-Thomson theory will affect clinical practice remains to be seen. Experts, however, advocate caution in factoring the Fisher-Thomson theory into the decision to prescribe SSRIs.

“I would not be in favour of scaring people away from taking SSRIs on the basis of these speculations. The vast majority of people for whom these drugs are prescribed are suffering substantially from their mental disorders and have markedly reduced quality of life,” says Lorrin Koran, Professor of Psychiatry at Stanford University, who specialises in compulsive behaviours.

Nick Kosky, consultant psychiatrist and clinical director at North Dorset Primary Care Trust, says that since most patients are on antidepressants for relatively brief periods, the Fisher-Thomson warnings about reproductive and relationship risks might be “a little histrionic”. “How long do people stay on antidepressants? Actually not that long as a fraction of their reproductive lifespan,” he notes. “There’s no evidence that once the SSRIs are withdrawn that sexual dysfunction persists in the long term.”

Fisher says she is by no means suggesting that SSRIs be done away with. “I’m not a psychiatrist or a medical doctor. I’m just telling people to be aware of what they could be jeopardising,” she says. Thomson agrees. He says that programmes can be altered or other medications can be used to mitigate against some negative side effects of SSRIs, so avoiding them entirely would be too extreme in most cases.

“They’re crucial drugs. They’re very important and I have my patients use them. I don’t want to be misunderstood here,” he says. “I think that they save lives.”

MAKING US FEEL GOOD