More than 90 percent of the world's 16 million injecting drug users are offered no help to avoid contracting AIDS, and governments that ignore them risk a spiralling public health crisis, drugs experts said.
-- Most injecting drug users have little or no protection
-- Experts say governments need better grasp of drug science
-- Critical problem in Russia, China, Malaysia, Thailand
A "critical health problem" is growing in places like Russia, China, Malaysia and Thailand, they said, where drug users are a neglected population in the fight against AIDS and the human immunodeficiency virus (HIV) that causes it.
Injecting drug use is an increasingly important cause of HIV transmission in many countries around the world. Users can spread the virus in blood by sharing needles with an HIV-infected person, and pass it on by having unprotected sex.
Of the estimated 16 million injecting drug users world-wide, 3 million are thought to be HIV-positive, and drug users are thought to account for 10 percent of all those living with HIV.
In Russia, for example, around a million injecting drug users are living with HIV and some 65 percent of new HIV infections there are thought to come from injections.
"Although the number of countries with core HIV prevention services is growing, the level of coverage in injecting drug users is poor in many countries," said Bradley Mathers of the University of New South Wales, Australia, who led a study on prevention efforts published in The Lancet medical journal.
Infection prevention steps like providing needles, condoms and substitute drugs like methadone - collectively known as "harm reduction" - are seen by many experts as key to halting the spread of HIV and AIDS, but some governments are reluctant to provide them for fear of being seen to condone drug use.
Gerry Stimson, director of the International Harm Reduction Association, accused such states of "playing politics with people's lives" and said millions were at risk as a result.
UNAIDS estimates that around 30 per cent of HIV transmission outside sub-Saharan Africa is driven by unsafe injecting practices. Stimson also pointed to Russia as a particular problem, saying injecting drug use in the region was now driving the fastest-growing HIV/AIDS epidemic in the world.
Mathers and his team of researchers looked at the provision of services to prevent HIV spread injecting drug users.
They found global coverage is very poor, but also varies widely. Worldwide, only 8 percent of injectors have accessed needle and syringe programmes in the past year, but that ranges from an estimated 100 percent in Ireland and the Czech Republic to under 3 percent in China, Malaysia, and Thailand.
"HIV prevention treatment and care services for injecting drug users are clinically effective, but to exert a population-level effect they need to be delivered to scale," they wrote.
The current level is "not sufficient to prevent, halt or turn around the HIV epidemic among this at-risk population." Don Des Jarlais of the Beth Israel Medical Center in New York said the poor coverage suggested some authorities should work to bring their policies "in line with scientific evidence".
"Long-term sustained efforts to protect the health of individuals who use both licit and illicit drugs might require that policy makers acquire a basic scientific understanding of drug use and addiction," he wrote.