By Daniel Dickinson
BBC News, Zanzibar
Just a few minutes walk from the winding picturesque alleyways of Zanzibar's historic and much-visited Stone Town is a sight that most tourists will not get to see.
Tourists come from Europe to sample cheap heroin and cocaine
Crouching in small fishing boats and dugout canoes on the shore of Malindi, Stone Town's port are a number of young men injecting themselves with a cocktail of heroin and cocaine.
It is a scene at odds with Zanzibar's image of an exotic beach paradise for well-heeled tourists, but for a growing number of Zanzibaris this is the reality of life on an impoverished island off the coast of Tanzania.
Saluum Ibrahim Jiddawi started taking drugs when he was just 15 years old.
His reasons for doing so were probably no different from teenagers anywhere in the world; he thought it was cool, his friends were doing it, he was bored at school.
And his life unravelled along predictable lines.
He graduated from smoking cannabis to injecting heroin and over the 15 years of his addiction, lost all his friends, his self-respect, put his family under huge stress and took to stealing and lying to feed his $15-a-day habit, a heavy financial burden on an island where the average wage is less than $1-a-day.
Saluum managed to kick the habit two years ago and now runs an outboard motor repair shop on the Malindi shoreline where addicts remind him on a daily basis of the "biggest mistake" of his life.
"I wasted 15 years of my life, and I regret all the pain I put my family through," he said.
Saluum was lucky to get out of the drugs scene when he did as the temptation of drugs on the island is as strong as it has ever been.
"Drugs are more available now as Zanzibar is on the international drug routes, but the quality is deteriorating as cocaine and heroin are being mixed with flour."
Small packets of foil wrapped brown sugar, as heroin is called locally, is easy to pick up in Malindi for just $1, but because of the poor quality addicts are increasingly injecting rather than smoking it.
"Users prefer injecting as the drug goes straight into the blood stream and has a bigger effect," said Saluum.
Spread of HIV
And now addicts are adopting a new technique which is worrying drug abuse specialists.
Young men inject themselves with a cocktail of heroin and cocaine
It is called "flash blood".
A user injects heroin, then withdraws a syringe-full of blood which contains a smaller amount of heroin and which is passed to a second user who injects it.
The technique means that addicts who cannot afford to buy their own drugs can still get a fix, however diluted.
"Such sharing is terribly dangerous," says Dr Steven Nsimba of the Muhimbili University of Health and Allied Sciences.
"It could have devastating consequences for HIV/Aids. If the first person is infected the second person will get a direct transmission of the virus."
The prevalence of HIV is under 1% in Zanzibar, well below the 7% on mainland Tanzania, but Dr Nsimba believes that could change.
"The spread of HIV could be very fast depending on the number of people who are doing flash blood."
No-one knows just how many addicts are using the flash blood technique, although the health authorities in Zanzibar are now trying to gather reliable data.
Mgeni Hassan from Zayedesa, a local NGO which offers support to addicts, paints a gloomy picture.
"We are seeing the effects of drug abuse, the increase in crime. Young people do not know what they are doing. We believe every household in the urban centres has one or two children affected."
And it seems that Zanzibar may be getting a reputation as a place for drug tourism.
One hotelier, who wants to remain anonymous, said he had met tourists who came from Europe to sample cheap heroin and cocaine.
One recent case involving a British tourist ended in tragedy. A 26-year-old man collapsed and died after taking drugs he had bought on the island.
Most tourists will, of course, enjoy drug free holidays in Zanzibar and will not be aware of the growing local addiction problem.
The authorities on the island are no doubt hoping that Zanzibar never picks up a reputation as a drug-fuelled paradise.