There is concern British soldiers in Iraq and Afghanistan are being treated with a drug that has not been fully tested and licensed.
The drug is used in military trauma care by the Army
The Ministry of Defence says it authorised the use of blood-clotting drug NovoSeven only after an extensive review of the current evidence.
It added the drug had only been used twice and only in order to save lives.
But Lib Dem MP Phil Willis, chair of the Commons' science and technology committee, said he was unconvinced.
An MoD spokesman said the treatment had been administered twice in separate incidents in Iraq.
"On both occasions the individuals' lives were almost certainly saved by the treatment," he said.
"The NHS also recognises the benefits of this treatment in similar circumstances - and has advised us that UK hospitals have also used the drug to treat severe trauma patients."
'Best possible advice'
But Mr Wilis says troops must not be given drugs not fully licensed for UK civilian use.
"Our soldiers are going into battle in both Afghanistan and in Iraq. They're risking their lives on a daily basis," Mr Willis told BBC News.
"The last thing we should be doing is actually treating them with any drug which may not in fact be fully licensed to be used on civilians in the UK."
Mr Willis, the MP for Harrogate and Knaresborough, added: "If you shouldn't be using it through Nice [National Institute of Health and Clinical Excellence] in the UK, you shouldn't be using it on the battlefield in Iraq."
The Chief of Staff for the Adjutant General, Brigadier Martin Rutledge, who deals with personnel issues at the MoD, said they were "determined to provide the very best possible trauma care for seriously injured casualties in any operational theatre".
The drug had only been used on soldiers after "very careful trials", he added.
"If there was further evidence about its suitability we'd obviously look at that very carefully," he said.
"We're not using anything without the best possible advice, and the interests of our soldiers is absolutely at the forefront of our minds."
'Potential for harm'
NovoSeven, also known as Recombinant Factor VIIa, was licensed in 1999 as a treatment to stem bleeding in haemophiliacs.
There are further trials to determine its use to prevent bleeding in trauma patients with severe wounds, and for bleeding within the brains of patients with severe head injuries.
However its effectiveness and safety as a blood-clotting agent in these circumstances has not been proven.
Professor Ian Roberts, an expert in trauma care at the London School of Hygiene and Tropical Medicine, said: "Like all treatments there is potential for harm and it is not licensed for use."