As tourists stroll languidly through the narrow streets of Stone Town, the romantic city hums with life. Vendors sell oriental spices and colourful fabrics, while children play soccer between crumbling walls and men hurry in long gowns towards the mosque.
But when darkness descends over the historic town, Zanzibar's capital takes on a different life. Formerly bustling alleys are transformed into dim, shady passages where drug addicts hover to get their longed-for heroin fix. The town's dark secret: the island is a heroin stronghold.
The underbelly of this holiday paradise remains unknown to most tourists, however, who spend carefree vacations on the archipelago. The tropical island is mainly renowned for its spices and slave history and as a diving destination -- and its government wants to keep it that way.
Reliable statistics for heroin usage are not available, but the island's health ministry estimates that at least 7 per cent of Zanzibar's one million inhabitants are addicted to what is commonly called "brown sugar". NGOs say every 10th person is regularly using heroin.
"Heroin abuse is very common, especially among younger men. It is easily available and much cheaper than other drugs, like cocaine or ecstasy," says Masoud Haji, project manager of the Zanzibar Association of Information against Drug Abuse and Alcohol (Zaiada).
"There is no one on this island who is not affected by heroin. Everyone knows someone who is addicted -- a family member, a relative, a colleague or a friend," he says.
One shot of heroin -- called a kete on Zanzibar -- costs a mere R7. And those who can't afford it practise blood-flushing -- a method used by addicts to draw back a needleful of blood after they have shot up heroin and sell the thinned fix to the next person.
"Everyone here knows where to buy heroin and most addicts inject quite openly on the streets," says Haji. Those who pay attention can see used needles lying in the street corners and alcoves of Malindi, the northern part of Stone Town, near the harbour. But needles can also been found in the bushes around Forodhoni Gardens, a popular tourist hang-out in the heart of Stone Town.
Insufficient trade controls make East Africa a welcome transit point for drug traffickers. Zanzibar lies on a century-old shipping route from Afghanistan - the world's biggest heroin producer -- via India to East Africa.
The island's small harbour is often the first stop for drug traders, who smuggle their drugs from here in small fishing boats into Tanzania's capital Dar es Salaam. From there narcotics are trafficked into different parts of the continent and to Europe.
When a new delivery of heroin arrives on the island the whispered news travels at lightning speed. "Everyone who has some connection to heroin will hear within a few hours that mzigo [Swahili for "new luggage"] has arrived," says Haji.
The question why the government of the semi-autonomous archipelago, which belongs to Tanzania, doesn't get the problem under control, he refuses to answer.
But Abdulrahman Abdullah, an ex-addict, who works for NGO Sober House, is more blunt than Haji. He believes the heroin trade is flourishing because its high profits are in the interest of the government.
"We will never solve the heroin problem in Zanzibar because politicians, police and rich businessmen are all involved and get kickbacks for turning a blind eye. The island is so small. If the political will was there, the drug problem could quickly be put to an end," he says.
Abdullah has been clean for a year. The 36-year-old tried heroin for the first time as a student and was hooked. The drug controlled the next 17 years of his life. "I injected to live and lived to inject," he says. "Heroin has destroyed everything I had. I lost my family and my professional future."
To get money Abdullah became involved in armed robberies. "I spent a big part of my adult life in prisons and psychiatric institutions. It was hell," he says.
As part of his new start in life his goal is to help other addicts.
One of his protégés is 29-year-old Rama (not his real name), who is sitting on a bed in one of the sparsely furnished rooms at Sober House, where he has been a resident for the past two months. With the typical empty stare of a heroin user, he talks about his life.
It is already his second attempt to quit his decade-long addiction. Rama was clean for six months in 2009, but then suffered a relapse. "Only very few succeed in saying goodbye to heroin forever," says Abdullah.
With heroin, Rama's life changed drastically. The young man, who comes from an established, well-known Zanzibar family, quit school shortly before matric and started to steal to finance his R120-a-day drug habit -- big money in a country where the average daily wage ranges between R10 and R15. "I would have done pretty much anything to get my hands on heroin," he says.
When his family finally threw him out Rama's life went from bad to worse. The grandson of a high court judge, he started to prostitute himself to get his next fix. "I sold my body to homosexual sex tourists and with it my last bit of self-respect," he says.
There has only been one recent blessing: a few days ago Rama's HIV test came back negative. He is incredibly relieved, he says, because infection rates are high among addicts who share needles and do sex work.
Although Zanzibar's official HIV infection rate is only 1 per cent, every fourth heroin addict, or 26 per cent, is infected with the virus, according to Zaiada.