In Guatemala, behind barred and locked doors, thousands of drug addicts are offered treatment by Protestant churches. Christianity offers salvation for some but many are held against their will, and some are swept off the street by "hunting" parties.

"They grabbed me. They found me completely out of it on the streets, and they just grabbed me."

Marcos is a big guy. With closely cropped hair, and a huge expanse of chest, he is not the kind of man to tackle lightly. But Marcos was accosted by a group of men in Guatemala City and forcibly taken to a private, Christian rehabilitation centre.

"I was there for about a month and a half, and nobody knew anything about me. People thought I was killed or something, because that's what happens in Guatemala."

"I saw terrible things in that rehab - the owner used to beat up the girls. He would tie up the guys and roll them up like a taco in a piece of carpet, and leave them there for hours," he says.

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Marcos was freed when a friend came looking for him, and demanded his release. He doesn't think enforced rehab is the right approach and says it did nothing to help him quit his alcohol and drug habit.

"People came out madder and more furious. Instead of being rehabilitated, you just went out to get high again."

Marcos grew up in the United States - a refugee from Guatemala's civil war in the 1980s - but was deported back to his parents' homeland after serving a prison sentence. With family in California, the owner of the rehab centre saw Marcos as a money-making proposition - he tried, and failed, to get contact details for Marcos' family to ask them for money for Marcos' keep.

All that is behind him now - Marcos is clean, and is dedicated to mentoring young people.

As there is no residential, state provision for addicts in Guatemala, private rehabilitation facilities have filled the vacuum. There may be as many as 200 Christian centres in Guatemala, possibly holding 6,000 people, estimates Dr Kevin O'Neill, from the University of Toronto, who has made an anthropological study of the centres. It is not known how many of them practice the aggressive "hunting" Marcos experienced.

Image caption One of the private rehabilitation centres that have sprung up in Guatemala City

O'Neill believes Guatemala is confronting a surge of addiction. Its strategic location in Central America means the majority of illicit narcotics moving from South America to the United States make landfall here. And the fallout is a growing local market for highly addictive drugs like crack cocaine.

"It's increased the number of centres in the capital city. But it's also changed the culture inside the centres - the internal dynamics have become much more aggressive, and much more discipline-driven because of the rise of crack cocaine," he says.

The founder and director of the Rescatados del Abismo, Rescued from the Abyss, centre is Pablo Marroquin, a born-again Christian and former drug addict.

"I'd been in other rehabilitation centres, but I wanted to make mine more personal. I put it in the hands of God - he's the only one who can rescue us from drug addiction," he says.

Marroquin lives on the ground floor of an unremarkable building in Guatemala City with his family, his budgerigars, and a pack of small, snappy dogs.

On the first floor, behind a locked, barred door, 54 addicts mill around. Many of them will not be allowed to leave for at least three months - but it could be years. Only the addicts' families or the director himself sanction the release of those interned here.

It is a confined space for so many people - the size of a large, three-bedroom flat. Off a common area, there is a bathroom, a room stacked with roughly-constructed bunks for those with privileges -most inmates sleep on the floor - and a bedroom for the six women internees.

Currently, the smooth running of the centre is down to Carlos - an internee who has been into rehab more than 30 times to try to overcome his addiction to crack cocaine and alcohol. Carlos imposes discipline and punishment at Rescatados del Abismo.

"When people arrive they can be very violent, and the only way to respond to that is with violence. It makes me uncomfortable, but it's extremely important to maintain discipline here," he says.

Image caption Carlos, an internee himself, maintains order at Rescatados del Abismo

Forcing an internee to clean the floors or to work at night are other forms of punishment.

Internees are partly controlled by compulsory attendance at meetings. They spend seven hours a day telling and re-telling each other their stories, charting their descent into addiction. These meetings are the only "therapy".

They are not structured, there is no psychologist or doctor involved, and no one is allowed to leave the room without permission. While listening to the testimony, the residents sit in shadow - the barred windows of the meeting room are covered with thick yellow corrugated plastic.

It is impossible to see the street from anywhere inside the centre.

"The vast majority, I would say 95% of the internees are here against their will," says Carlos.

Now he's there, we have a bit more peace of mind - if he were in the street, anything could happen here in Guatemala Carlos Ruiz, brother of Victor, an internee

When desperate families call the centre asking for help with a substance-abusing loved one, he often accompanies the director to go and pick an addict up.

"It's our role to bring them here, and that can mean using handcuffs like the police. Sometimes a family will say their son is very violent and has a knife or machete. In those cases we tie him up before bringing him here."

Carlos believes this is legal in Guatemala. A ministerial accord of 2006 states that an addict can be interned when they are not in a fit state, but once they have recovered sufficiently, they must give consent. By all accounts, this rarely happens.

At the Ministry of Health, the regulation and co-ordination of the centres comes in the shape of just one man - Hector Hernandez has worked for the last 14 years to try to improve the centres and make them more humane. He has closed some, but he says forced detention has never been proven.

"Not even the attorney for the defence of human rights has been able to establish there are people detained against their will - there's been no confirmation of any allegations made," he says.

During the compulsory meetings at Rescatados del Abismo, Victor Ruiz reads his well-thumbed bible. An abuser of crack cocaine and alcohol, he has been here for three months. Victor believes only God and Jesus Christ will rescue him from addiction.

"I think I'll be here for another five months, it all depends what my brothers decide," he says.

Before he came to the centre, Victor was living on the streets. One day when the family could not find him anywhere, his older brother, Carlos Ruiz went to look for Victor at the morgue.

I experienced God's mercy - he rescued me Pablo Marroquin

"I was looking at the photos of dead people to see if one of them was him. It's really shocking. These things stay with you, it's like you die a bit too," he says.

After Victor was attacked in the street by someone with a machete, the family had him interned in Rescatados del Abismo.

"Now he's there, we have a bit more peace of mind - if he were in the street, anything could happen here in Guatemala."

The director of Rescatados del Abismo, Pablo Marroquin, has little patience with arguments about whether the regime he runs violates the rights of internees, especially when they are held involuntarily.

"What about families? What we do is give families peace, so their loved one doesn't get himself into trouble. And so that he won't kill them," he counters.

Image caption Adverts for other rehabilitation centres in Guatemala City, with the left one titled "Warriors of Christ"

There is no data about how successful the rehabilitation of addicts is in Guatemala. In 2012, the United Nations called on all member states to close compulsory drug detention and rehabilitation centres.

"There is no evidence that these centres represent a favourable or effective environment for the treatment of drug dependence," declared the UN statement.

Many experts believe addicts can never be forced to change - they have to want to stop. And in Guatemala there are many Christian establishments that will only take addicts on a voluntary basis.

But Pablo Marroquin, clean now for 22 years, is a testament to his own approach to rehabilitation.

"I experienced God's mercy - he rescued me. He brought me to a rehabilitation centre where I met myself, and I met God. And these days, I'm a happy man."

Listen to Linda Pressly's report from Guatemala City on Crossing Continents on BBC Radio 4 on Thursday at 11:00 BST - or find it soon after on BBC iPlayer.

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