By Brian Wheeler
Political reporter, BBC News
A controversial drug which can keep people awake for days has been tested by the UK military, MPs have been told.
Special forces sometimes have to stay awake for 48 hours or more
Modafinil pills - known on the drugs scene as "zombies" - are used to treat the rare sleeping disorder narcolepsy.
The Ministry of Defence reportedly stockpiled thousands of pills ahead of the Iraq war but they have never been given to combat personnel.
Defence contractor Qinetiq told the commons' science committee the drug had recently been tested for military use.
Qinetiq scientist Dr Anna Casey told the Science and Technology Committee the MoD funded research into stimulant and performance-enhancing drugs and dietary supplements.
"One is always looking for something that would give military personnel an extra edge," she told the committee which is investigating the use of such drugs in sport.
She said the military was not under the same constraints as the International Olympic Committee, which had banned Modafinil and another stimulant, Ephedrine, which she said had also been tested by the MoD.
But Erythropoietin, or EPO, which is used by athletics drug cheats to boost the production of red blood cells had been ruled out due to "safety concerns".
She stressed that no illegal substances were being researched by the MoD.
But she said Modafinil had been "shown to enhance physical and mental performance".
"There is still research going on into things like that. It doesn't mean they are being used. We are keeping an open mind," she told the MPs.
Modafinil has also been trialled by the US and French military but its use remains controversial.
It works by "turning off" a person's need to sleep, and allowing them to remain mentally awake for days on end.
Its makers say there are no side effects, but experts are worried about the drug being abused.
In the US, where it is easier to get hold of, revising students and clubbers are known to use it to keep going.
Speaking after Wednesday's hearing in Westminster, Dr Casey said Modafinil had recently been tested by Qinetiq, formerly known as the Defence Research Agency.
It had not yet been approved for use by British soldiers but Qinetiq had asked the MoD for funds to carry out further tests, she said.
"It is worthy of further research," she told the BBC News website.
Ephedrine, which is similar in effect to amphetamine or "speed", had so far been ruled out for use by British combat personnel due to its side effects, which included anxiety.
But caffeine was "something we may well end up using in the future," she added.
She said the MoD was also funding research into "human science", including the enhancement of the physical and mental performance of combat personnel.
Among other things, scientists are investigating new dietary supplements and remote monitoring technology, allowing soldiers' physical performance to be tracked in the field.
The consortium will also be looking at ways of improving the performance of combat personnel in hot climates such as Iraq, to cut down the amount of time, currently about a week, needed for them to acclimatise.
There has long been a demand for reliable stimulants for use by special forces, who may be expected to go 48 hours or more without sleep, and pilots on long flights.
The issue came under the spotlight in April 2002, when two US military pilots mistakenly bombed a Canadian infantry unit in Afghanistan, killing four.
During the ensuing legal arguments, the pilots' lawyers said they had felt under pressure to take amphetamines before the mission.