As a clinical psychologist, Frank Tallis worked for decades with patients who suffered from what was once called lovesickness. Now a full-time writer of both nonfiction and novels, he has collected some of the most memorable cases into his forthcoming book, The Incurable Romantic: And Other Tales of Madness and Desire (Basic Books, September 2018). We talked about love and madness and the connection between them.

[An edited transcript of the interview follows.]

Do you really think love is a mental illness?

Love can be a powerful and destabilizing experience. People often experience it as not wholly pleasant. You could say that ideas of romantic love are fundamentally delusional because the beliefs associated with romantic love just don’t correspond with reality. This idea that there is one special person out there who you are destined to meet—that is such a strong belief and clearly untenable. But it’s [one] that a lot of people share. It’s been consolidated by Hollywood and romantic fiction.

Are we all at risk of madness, then?

Providing you can function in the world, it doesn’t necessarily constitute a problem. [But] one example where ordinary behavior shades seamlessly into psychopathology is stalking. It’s a very upsetting, serious thing to stalk someone. Yet if you talk about the way people behave when they’re courting, they say they wait in a particular place on the off chance that a particular person might come along. There are quite subtle forms of stalking that we all do. Turn up the volume slightly on these behaviors and very quickly you cross a line into harassment or behaving in a way that can be described as disturbing.

What happens then?

The patients I saw, their lives began to break down. And, of course, when love goes wrong you have all kinds of problems that result like infatuation, psychopathological jealousy, heartbreak, inappropriate attachments, addiction. There are significant psychiatric sequelae to the intense experience of falling in love. It is something that we need to take more seriously than we do.

Why haven’t we?

For thousands of years doctors recognized lovesickness and conditions of longing and desire as a medical condition. [That was] replaced by an interest in sex. We don’t see romantic love being given consideration from a psychiatric perspective. Altogether my clinical training in psychology was about eight years. In those eight years I had one hour of formal education on love in the sense of love between couples in relationships.

Why is it that some people are more vulnerable than others?

You could speculate about biological vulnerabilities in their brains, you could speculate about their histories. For example, someone who is profoundly insecure because they were unloved as a child might be more vulnerable to psychopathological jealousy. But the particular factors [that] make one person vulnerable may be very different to the factors that make another person vulnerable.

What do we know about love and the brain?

There’s a neurochemistry of love that has been identified containing amphetamine and opiatelike substances—the chemical cocktail that is released when people fall in love. The transcendent states have been associated with oxytocin, a powerful attachment hormone. It’s also the case that when you fall in love the beloved becomes an all-consuming obsession. Some of the machinery that’s involved in sustaining clinical obsessions might also be recruited when one is having an experience of obsessional love.

Did most of your patients suffer from problems with love and desire?

My clinical specialization was anxiety disorders and particularly obsessive-compulsive disorder. The more I saw of patients who had fallen in love, the more I could see correspondences between the condition of being in love and obsessional illnesses.

Like the woman who fell madly in love with her dentist and was sure he loved her back?

The sovereign condition amongst conditions of longing and desire is de Clérambault’s syndrome, a kind of reciprocal delusion. It’s not very common. You not only fall in love with that person but you are absolutely convinced that they have fallen in love with you, [and] that it is destined. That patient was particularly interesting because of the purity of the phenomenon. She illustrated to me how we all walk along a precipice when it comes to mental health—the most stable person with a very ordinary life can suddenly succumb to an illness that takes them to the most curious and incomprehensible extremities.

The man you describe as the incurable romantic couldn’t accept the end of a relationship. I imagine that’s much more common?

Yes. In the case of the incurable romantic, apart from reciprocity, you get a lot of the symptoms of de Clérambault’s syndrome. You get someone stalking, absolutely obsessed, subscribing entirely to a romantic belief system that one can only be happy with this particular person. There is a denial of reality that is quite extraordinary. [He would say] “I know she said she doesn’t want to see me again. I know she said she’s going to call the police—but if I just had only a minute to persuade her, I think I could do it.” You sit there and think, “Oh wow, how can you possibly think that at this stage?” But these people are genuine.

And what about the man who slept with 3,000 prostitutes? You thought he was addicted, but not to sex.

That was the fascinating thing. In clinical practice you come across sex addicts all the time, [although] perhaps not as spectacular as seeing 3,000 prostitutes. What was really interesting about this guy was that the sex was a way to form relationships with prostitutes and the goal was eventually for them to fall in love with him. He was addicted to the feeling of being fallen in love with. Once he got them to say “I love you” he moved on.

That is really so sad.

Yes, one shouldn’t let the curiosity of these phenomena obscure the sadness.

Did you feel you helped these people?

The book is called The Incurable Romantic. Sometimes there is no cure. Often the way we see psychotherapy represented is unrealistic. It is actually unpredictable, messy and uncontrolled. Things come up, people do and say things that are unexpected, there are dead ends. Sometimes people stop turning up. You never find out the end of the story. I purposely chose cases that were difficult to treat or unsatisfactory. I hope it makes the book more interesting.

Who is the book for?

It’s for anyone who has ever Googled a former romantic partner or looked them up on Facebook. As soon as you admit to that, it takes you to interesting places in terms of understanding the way the mind works, the importance of love and also love as a vulnerability to psychopathological states.