In Bangladesh, where alcohol is banned, increasing numbers are turning elsewhere to get their kicks. And the drug of choice is codeine-based cough mixture.

Codeine-based cough syrups are banned in Bangladesh but perfectly legal in India from where it's being smuggled in. Shafiq says he's at the rehab centre to try to rid himself of his addiction to Phensedyl, a popular cough remedy on sale at about $1.50 in India but for much more on the streets of Dhaka.

This rehabilitation centre in Dhaka is treating those addicted to it. Treatment at the centre lasts four months at a total cost to the addicts of $500.

"When I take Phensedyl I feel very strong, I feel very energetic, but after some time when the feeling ends, I feel sick and less energetic and to solve that problem I was taking Phensedyl again. I spent 12 years taking it this way," Shafiq says.

Professor Mohammad Seyedur Rahman, Bangabandhu Sheikh Mujib Medical University (BSMMU) pharmacology department, says even the cough syrup legally sold in Bangladesh contains codeine subsitutes - not as addictive but they still give a high.

"The addicts, they tried substances that contain similar things like Phensedyl, particularly codeine was replaced by pholcodine or pseudoephedrine, they try with that, and chlorpheniramine is available as antihistamine," he added.  

Data is sketchy on the scale of addiction in Bangladesh. Surveys by academics and non-government organisations suggest up to 1.5 million people are hooked on cough syrup.