They loiter on pedestrian bridges, puffing on pipes. They squat behind bushes and palm trees in leafy parks to get their fix. Even doctors and nurses are users.
Iran's drug problem has become a national epidemic, health ministry officials and local doctors say, drawing the poor as well as the affluent, the secular as well as the pious, to an assortment of hard drugs including crystal meth, painkillers, synthetic hallucinogens and heroin and opium trafficked from neighboring Afghanistan.
"No walk of society is immune. Even the sons of Islamic clerics are patients in our clinics," said Dr. Hasan Razavi, who runs a small rehabilitation center in western Tehran.
The United Nations Office of Drugs and Crime says Iran has one of the gravest addiction crises in the world. Health ministry officials estimate there are 2.2 million drug addicts in this country of 80 million, 2.75% of the population, but doctors who operate some of the hundreds of government-sanctioned rehab clinics nationwide believe the actual figures are higher.
By comparison, according to the 2013 National Survey on Drug Use and Health, an estimated 21.6 million Americans had a substance abuse problem, or about 6.8% of the population.
One reason for the drug problem is availability: Iran lies on the main trafficking route for poppy, the source of opium and heroin, from Afghanistan to Western Europe. Iran accounted for the most opiate seizures in the world in 2014 as Afghan drug production has risen.
Doctors also say the economic stagnation brought about by international sanctions has provoked such social frustration and immobility that many are driven to substance abuse.
Among affluent young Iranians, use of methamphetamine, known as shisheh, or "glass," also has risen because it is seen as a way to lose weight, focus on an exam or get high for parties.
Opium has been cultivated for centuries in Iran, where poets going back to the 10th century wrote of the plant's healing properties. But in recent years, more opium and heroin from Afghanistan are finding their way into the country even though Iran has spent tens of millions of dollars on fortifying the 600-mile border with concrete barriers and deep ditches.
"Sanctions and isolation from the international community, unhappiness due to being unemployed, even among the educated classes of society — and even unhappiness among the rich — these are all among the main causes of the increasing number of illicit drug abusers," Razavi said.
In downtown Tehran, amid the stately buildings of the Qajar Dynasty, which ruled Iran until 1925, petty dealers weave through crowds and almost whisper the word "Darou," which means medicine — an offer to sell anything from prescription painkillers to synthetic narcotics. A day's supply of opium costs as little as $1 in an economy where the average high school graduate earns about $10 a day.
Though many Iranians continue to hold jobs and live productive lives despite their drug use, the phenomenon of homeless addicts wandering the streets, often wild-eyed and disheveled, has become so common that there is a Farsi word for them: motejahr. The head of the Iranian police's anti-narcotics department, Gen. Mohammad Masoud Zahedi, recently told reporters that 50,000 to 60,000 Iranians fit this category.
Shabanali Mirshekar, a violinist from northeast Iran, first used opium when he was about 12 years old, when he was invited to play at village gatherings. His father had started to smoke opium to treat pain in his legs.
As he grew older, opium "made me forget all my troubles," said Mirshekar, 40. "I got high and played all night."
His addiction led his wife to seek a separation. He sleeps in a grubby, $1.40-a-night hostel for musicians in a crime-ridden part of southern Tehran.
A few times a week, Mirshekar visits Razavi's clinic for a dose of methadone, a synthetic opiate used to wean addicts off of drugs.
Without the methadone pills, he said, "I can't stand on my feet. My calves and legs hurt and I can't play the violin to earn a living," he said.
Mirshekar said the pills he gets are more than what he needs; he sells the surplus on the streets. Doctors acknowledge there is a thriving underground trade in domestically manufactured methadone — itself an addictive drug — which sells for double the health ministry's price of $1.40 for 100 pills.
"The gap between the black market price of methadone and the official price we get from the health ministry is so big that it is provoking abusers and traffickers to sell them in the black market," Razavi said.
Inside Razavi's 800-square-foot clinic, 250 patients have sought treatment for drug habits over the past three years. Razavi's patients have included surgeons, operating-room nurses, managers of state-owned companies, teachers, salaried workers, artists and actors – yet in the last year, he said, none could be said to have gone clean.
Some clinicians argue that methadone treatment merely replaces one dependency for another and that Iran would be better off sanctioning small amounts of opium for addicts to reduce their dependency. Razavi disagrees, saying that the usual 36-hour life of a methadone dose — compared with four or five hours for the typical dose of heroin — allows the patient to lead a more productive life.
Iran's theocracy has tried harsh anti-drug measures, sentencing huge numbers of convicts to death row. Last year, hundreds of Iranians were reportedly executed for drug crimes, prompting a movement among lawmakers and activists to abolish capital punishment for nonviolent drug offenses.
But some say the scourge of drugs has been treated less severely than alcohol abuse because drugs are believed to interfere less with the Islamic practice of praying five times a day.
The health ministry has authorized 8,000 rehabilitation clinics such as Razavi's to begin methadone maintenance therapy. Razavi has hired part-time psychologists and keeps detailed dossiers on each patient.
But doctors say many private rehab "camps" have also cropped up, some of which serve as little more than minimum-security jails where families can deposit drug-addicted relatives for less than $200 per month.
In such facilities, doctors say, drug users are less likely to be treated than to fall in with criminals and traffickers.
"But as long as nobody is killed or wounded, or no one files a lawsuit against the unauthorized camps, they are tolerated by police," Razavi said. "At least for a short time, it means fewer addicts wandering in public places."
Special correspondent Mostaghim reported from Tehran and staff writer Bengali from Mumbai, India.
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