By Frances Harrison
BBC correspondent in Tehran
"If I wasn't here I would be dead or in prison," says Behrouz Shahkuri, one of 200 drug addicts who receive methadone tablets daily at the Persepolis centre in south Tehran.
It is the first methadone programme in Iran in a non-governmental organisation (NGO) setting - a pilot project aimed at tackling Iran's growing addiction problem in a new way.
Addicts are given clean equipment and medical checks
Until recently the emphasis was on reducing the supply of heroin - now it is shifting to reducing harm, because of the fear that HIV is spreading among injecting drug users.
Persepolis offers addicts a package of syringes, clean needles, tape, alcohol pads, condoms and distilled water - as well as food, clothes, a bath and medical attention, including wound and abscess management.
Dr Bijan Nasirimanesh, who runs the programme, says that if more than 5% of injecting drug users are HIV-positive then a country is on the verge of an explosion of HIV to other parts of society.
"I must say that in Iran we have passed this line."
Of 500 addicts he has tested in his drop-in centre, 25% were found to be HIV-positive.
Persepolis tries to promote safe sex but it has to be culturally sensitive in a country where extra-marital sex is illegal.
Dr Nasirimanesh runs the Persepolis programme
Dr Nasirimanesh says he is able to offer condoms to a teenager but not in the way he would in Australia for example.
He asks if the teenager's father is a drug user and "does he understand about safe sex?" - and then he tells the teenager that he can teach his father how to protect himself.
"In this way indirectly we show to the people what a condom is and what it protects against," Dr Nasirimanesh says.
But for Behrouz Shahkuri it is too late. His father was a drug dealer in Kurdistan and it was only a matter of time before he too became addicted.
In prison, Behrouz thought he had contracted hepatitis. When he was released, he went to a clinic because he did not feel well.
While having a second blood test he asked the nurse what was wrong. Without any preamble or counselling, she told him he probably had Aids.
Drug addiction has destroyed Behrouz's life
"It was as if someone poured a bucket of hot water over me. I was about to have a heart attack," he says.
When the test confirmed he was HIV-positive, Behrouz tried to kill himself four times.
"I wanted to throw myself in front of a car but my dad stopped me. I cut my veins in the shower to commit suicide but I didn't succeed in killing myself."
Many of the staff at Persepolis are former addicts. Nabud Islami injected heroin for 10 years and was in and out of prison.
"I never imagined I would be doing this," Nabud says.
"Whenever I gave up in the past it was always because someone beat me up or a policeman took me away to prison but this time I gave up just because of the love and affection I received from the doctor."
But he adds that the doctor is just a factor - the main point is addicts help each other to kick their habit.
Nabud (left) now works to help others kick the addiction
"After work I go out into areas where addicts are shooting up and I talk with them and they listen to me," says Nabud, who has become an example to others of what they can achieve with the help of methadone treatment.
But Persepolis has a waiting list of 300 people. They are short of funds and space and simply cannot cope with the numbers they receive.
And they are aware that if their approach is to have an impact on the spread of HIV in time it needs to be replicated fast as part of a national strategy.