By Ania Lichtarowicz BBC Health reporter

More heroin is available now

A study of more than 200 intravenous drug users published in the Journal of Drug and Alcohol Dependence shows that needle sharing has increased three-fold since the start of the conflict in 2001.

This has put them and others at greater risk of contracting HIV, the virus that causes Aids..

Rates of HIV and Aids in Pakistan have historically been low, but this latest research suggests the situation could change rapidly.

'Shared needles'

Before war began, 57% of intravenous drug users shared needles, but this rose to 76% after the war started.

It appears that increased police presence as well as changes in heroin purity, availability and price have led not only to rises in needle sharing, but also in the numbers of intravenous drug users.

Earlier studies by these scientists showed that 30% of injecting drug users in Pakistan are paid for donating blood.

If needle sharing has increased, then so has the spread of blood-borne diseases like HIV and certain forms of hepatitis - and could, through donated blood, be passed onto the rest of the population.