Of the many alleged victims of the film producer Harvey Weinstein, perhaps the most overlooked and least sympathised with are so-called sex addicts. They may not have directly suffered at his hands, but in their own way they have felt a harsh blowback from his actions.

When the damning testimonies of sexual abuse began to pile up, Weinstein denied allegations of non-consensual sex but did admit to a problem and is believed to have sought sanctuary – and treatment – at the Meadows, an upmarket sex addiction rehabilitation centre in Arizona.

It runs a men-only programme entitled, a little ironically in Weinstein’s case, Gentle Path, which lasts 45 days. Participants are assessed as to their position on the sex-addiction spectrum, according to a programme designed by Dr Patrick Carnes, the leading expert in the field who first popularised the term “sex addiction”. Level 1 is overuse of porn or masturbation and visiting prostitutes; Level 2 is victimisation, exhibitionism, voyeurism and harassment; Level 3 is rape, incest, child sex abuse. Carnes believes most people with addiction problems are a Level 1 or 2.

The residents of the centre undergo group, individual and family therapies. In a “nurturing community”, they also engage in meditation, exercise programmes, spiritual practices and lectures. By all accounts, the food and accommodation leave little to be desired.

The aim is for residents to “gain the courage to face difficult issues, including grief and loss; heal from emotional trauma; and become accountable for their own feelings, behaviours and recovery”. The actor Kevin Spacey, another accused of predatory sexual behaviour, is also said to have attended the Meadows.

To many observers, Weinstein’s sex-addiction treatment appeared like the last refuge of the Hollywood scoundrel, a handy excuse when all else had failed: “It’s not my fault. It’s my damaged psyche!” Even the term sex addiction seems a little too convenient: a vice masquerading as a pathology, an excuse dressed up as an illness. It’s not a condition that is recognised by the Diagnostic and Statistical Manual of Mental Disorders [DSM], the bible of the American Psychiatric Association. There are no physical symptoms of withdrawal, as there are with, for example, alcohol and drug addiction.

However, therapists in the field speak of a growing sexual addiction “pandemic” that a mixture of shame and misunderstanding has kept hidden. Paula Hall runs the Laurel Centre, a specialist organisation in Leamington Spa dedicated to sexual-addiction therapy. She believes the publicity surrounding recent high-profile scandals has been detrimental to an understanding of what she believes is a very real and growing problem.

“There is a percentage of people who are sexually addicted and offend,” she tells me in her London office. “It absolutely in no way excuses the offending, and is a completely separate issue. So if Harvey Weinstein is a sex addict I hope he will get the help he needs. And if he is guilty of what he’s been accused of, I hope he gets locked up as well. They’re not mutually exclusive. Unfortunately, it has again cast doubt on the whole sex addiction label and left ordinary guys finding it harder to reach out. As one client said to me: ‘I’m worried that even being here, people will assume that I’m predatory.’”

Hall insists the debate about whether or not sex addiction is a clinically accepted condition misses the point. “Look,” she says, “bereavement is not in the DSM, but no therapist says: ‘Sorry, bad luck. I can’t see you.’”

The clients who come to her seeking help are, Hall says, often in a state of great distress and not infrequently suicidal. They want to stop doing what they’re doing: be it watching porn, visiting prostitutes, or using the internet to organise fleeting sexual encounters. But they can’t, in much the same way that the compulsive gambler can’t stop gambling, even though it’s destroying his life.

When things were at their worst, Rob Joy would hold his head in tears of frustration and smash another mobile phone, while his wife lay asleep in blissful ignorance upstairs in bed. The 39-year-old owner of a decorating company would destroy his phones to stop himself from viewing pornography and texting, or “sexting”, women in provocative or inappropriate ways.

As compulsive sexual behaviours go, Joy’s were a long way from the most extreme. On Carnes’s scale, he would classify as Level 1. But it was enough to lead to a crisis that saw him lose his job, his friends and, effectively, his home. What made the situation particularly difficult was that his job was that of an Evangelical Christian pastor in a respectable Northamptonshire market town.

A short, good-looking man who buzzes with words and energy, he felt overwhelmed by the work which, aside from the financial responsibilities, included advising married couples on the issue of adultery. He and his wife had a two-year-old child and one-month-old baby, and Joy had taken to unwinding with a couple of drinks in the evening which, he admits, lowered his inhibitions. Then he would stay up looking at porn and seeking digital flirtations.

“I wanted the conversation to go to the point of sexualised conversation,” he recalls at his base in Luton. “Masturbation and then finished.” That was the line beyond which he didn’t want to cross, out of respect for his wife, although on a couple of occasions he did transgress and he was mortified with shame and guilt.

One day three years ago, he tried to steer a text conversation with a woman from his congregation in a similar direction, but she reported him to church leaders who conducted an investigation. They looked at Joy’s computer and found porn sites and incriminating emails. His world fell apart. Within days he was dismissed, ostracised by his community and had to move away from the village. The family spent months sleeping on his in-laws’ sitting room floor. In the aftermath, Joy felt humiliated, depressed, and full of remorse. It was at that low point that he decided to seek treatment for sex addiction.

The vast majority of sex addicts who seek help are male, though many studies, including Paula Hall’s own, have shown that 30% are female. So why are they not seeking help? “There’s a lot more shame for women,” says Hall. “We accept a man being a bit of a player, a bit of a lad. But a woman’s going to get a lot more societal shunning.”

One therapist in Bristol, Gary McFarlane, a member of the Association for the Treatment of Sexual Addiction and Compulsivity, who treats people throughout the UK and around the world via video link, told me that, broadly, he found that while men were more likely to be sex addicts, women were more often love addicts.

Hall, however, does not recognise the distinction. “All addictions are basically symptoms of something else,” she says. “For many people it’s a symptom of a lack of self-worth, a way of seeking validation and affection, of feeling wanted and feeling needed. That is equally true for male clients.”

When she first started working in the field, most men sought treatment after being found out by a partner. The therapy was part of an ultimatum. But, increasingly, her clients are coming of their own accord because they can no longer function with their dependency – some have spent “tens and tens of thousands” on their sexual habits. There are times, however, when the dependency still wins out. “One guy stopped coming,” she says with a broad smile, “because he said he couldn’t afford both me and ‘the girls’.”

In nearly all cases she sees, the entry point, the gateway drug as it were, is pornography. Like the other therapists I spoke to, Hall believes there has been a generational shift in behaviour as a result of the digital ubiquity of porn.

“The problem is hidden from the person themselves. You can’t drink alcohol or take drugs for five hours and not feel it the next day, or people around you not notice. You can watch porn for eight hours every single day and no one is going to know. There are no side effects.”

Yet Hall is not interested in pathologising watching pornography, or indeed any other sexual behaviour involving consenting adults. “Ultimately the type of the behaviour is not what defines an addiction, just as if you’re an alcoholic it doesn’t make any difference if you drink whisky or gin. It’s the dependency and inability to stop that defines the problem.”

Owen Redahan, a sex addiction counsellor who has a practice in London’s Canary Wharf, agrees. “I get clients coming in who say they must be addicted to sex and you go through it and they aren’t.”

Some people have high sex drives, which should not be confused with sex addiction. “Most of the people I work with,” says Hall, “have long ago forgotten what their sex drive is.”

She compares the situation to the chronically obese person who can’t stop eating. They don’t experience hunger and in a similar way the sex addict doesn’t feel sexual desire. What they are in search of is the dopamine hit from a risky or inappropriate sexualised encounter, the self-soothing buzz that will momentarily block out the underlying feelings of self-loathing and anguish. But those feelings soon return and the sufferer seeks respite in the next sexual encounter.

That is the cycle the writer Erica Garza describes in her memoir Getting Off: One Woman’s Journey Through Sex and Porn Addiction. It’s a compelling read about sexual compulsion. “I started watching mild porn,” she tells me, “but to get that feeling of shame I had to watch harder and harder porn. I had to go to extremes. I had to find something that I thought was shameful and disgusting and that leaked out into the rest of my life.”

Pretty soon Garza was picking men up in bars and having unprotected sex with them, which left her with an emptiness she vainly tried to fill with more reckless sexual behaviour. What’s unusual about her case is the pattern of her recovery. As she tells it in her book, she met a man she fell in love with and sex became a medium for expressing love rather than anaesthetising pain. In her new “healthy” relationship, she avoided pornography and put a premium on monogamy, because that felt the safest way to live her life.

No one can be certain, but by some assessments the relapse rate for sex addiction seems to be quite high, partly, perhaps, because of the ease and proliferation of casual or commercialised sex, and pornography.

“After a while,” says Garza, the monogamy and no pornography strictures “felt inauthentic, as if I was cutting off a part of my sexuality. That didn’t feel right.” Now she and her husband have boundaries in place, though she seems to suggest that they’re quite permissive – at least by the standards of most recovering sex addicts.

And this is where sex, as a form of addiction, is a problematic concept. The alcoholic, the drug addict, the compulsive gambler all know that recovery involves total and, ideally, permanent abstinence. But what of the sex addict? Celibacy is not much of an answer. So what is?

“Identifying what is positive sexually to that person,” says Hall. “When, after a sexual encounter, you feel worse about yourself, that’s not a good sign. So the exercise we do is write down what is definitely OK and what is definitely not OK, and they’re allowed a temporary space, which is ‘iffy’.”

“Pornography almost certainly is not OK ever [for the sex addict], but it can be OK – and this is the critical understanding of sex addiction – if it is coming from the place of libido, from sexual desire, as opposed to dopamine arousal. Masturbation is the classic one. When is it OK? When is not OK? Not in Sainsbury’s.”

For Rob Joy, the road back from sex addiction has been long and difficult. Earlier in his life he underwent a dramatic change when he became a Christian. For 10 years before that, from the age of 16 to 26, he’d been a drug addict, and for most of that time a crack addict. Yet when he took to religion, he was able to stop overnight. He got married to a fellow believer, and told his story of overcoming drug addiction, criminality and gang life to rapt audiences around the country. But not even his love of God could stop his sexual compulsions.

Like many addicts, Joy traces the source of his problem to childhood trauma – in his case being introduced to pornography as a four year old by older children on his estate. His father, he says, also had a lecherous attitude to sex and, in fact, died in a brothel while having sex with a prostitute.

“You don’t want to become a victim,” Joy says, “but sex addicts are victims, too. You see people being named and shamed at the moment, and their behaviour is absolutely wrong and it needs correcting, or punishment, but the way we are shaming people is causing so much more damage to them, because most of them probably have similar stories to me. Their brains have been set like wet concrete at an early age.”

Joy, who also describes himself as “an author and itinerant Evangelist”, undertook treatment with Gary McFarlane, and that made him come to terms with the nature of his problem. He now has a security app on his phone and his laptop that alerts his wife to any ill-advised communications. Recently, he sent a message to her that ended with a loving “XXX”, which triggered an alarm owing to its pornographic connotation.

“I genuinely do not want to watch porn,” he says. “I do not want to dishonour my wife or degrade the women on the internet. I weep over it. I walk into shops with my 12-year-old son and magazines are at eye level. And I say, sorry that’s wrong. You can go two or three weeks and one day you just go, I need it. And the risks you’ll take in being caught are ridiculous.”

Luckily his wife, Lydia, has been extremely supportive and understanding.

“Obviously I was very hurt,” she says. “I went through different phases. At first I felt sympathy, because I saw how people were looking at him with total disgust. But there were also times when I just felt anger, mostly at the situation, but that came out as being more distant from him.”

Lydia never lost her belief in his strength of character but, watching his efforts, she also regained her trust. Having gone through the experience, she has contributed to a book he has written about his addiction.

“I want to help people and the partners who feel that they can’t forgive or understand it,” she says.

Sex addiction may not have made it into the psychiatric manuals, but it does seem to have entered plenty of people’s lives. In many respects it’s a modern phenomenon, born of increased opportunities, the anonymous and hyper-sexualised online world, and the forlorn urge to find transient respite from the all-too-common internal voices of angst and self-doubt.

Yet, like some fiendishly adapted parasite, it’s made its home in humanity’s oldest and most vital urge. And this means that, whether or not clinicians agree that it exists, it’s unlikely to go away.