The Canadian military kept 250 soldiers home from Afghanistan during the past year because they tested positive for drug use, officials have confirmed.

The military told CBC News that it has tested about 6,800 soldiers since mandatory drug testing of troops headed for Afghanistan began in September 2006.

Some soldiers were tested more than once, with about 9,500 tests done to date. Some of the soldiers were retested because they provided diluted urine samples, something the military views as an attempt to cheat the system.

CBC News obtained the results of tests done between September 2006 and May 2007 through the Access to Information Act. The military then provided numbers from May until present. Names of soldiers were not released.

Test results from September to May show that the majority of soldiers who failed the test tested positive for marijuana. Some others used harder drugs, such as cocaine, methamphetamine and amphetamines.

"It's a particular concern because we are in Afghanistan, they are in a combat situation and they have to make split-second decisions, life or death, and we need them to be able to do that without the influence of illicit drugs," said Canadian Armed Forces Brig.-Gen. Ian Poulter.

Poulter pointed out the illicit drug use was found in less than four per cent of the soldiers and said that number represents a smaller percentage than drug use by the general population.

But retired Col. Michel Drapeau said it's still a "big deal" because it means the army is forced to ask some soldiers to serve in Afghanistan for another term.

"That means probably that … somebody else who steps in are probably individuals that have already been in Afghanistan…. So is it serious? Yes, it is."

Gen. Rick Hillier, chief of defence staff for the Canadian Forces, has taken a zero-tolerance approach with troops, and all soldiers who test positive for illicit drugs are kept home.

"You can't have people driving large, dangerous equipment, handling guns if they're abusing substances," said Senator Colin Kenny, the chairman of the standing Senate committee on national security and defence.

The military says it plans to expand the drug testing program to include blind testing, which will encompass the entire Canadian Forces, not just soldiers slated for duty in Afghanistan.