A common blood pressure drug could help people who have witnessed traumatic events, such as the London bombings, to block out their distressing memories.
Witnessing events such as the London bombings can lead to PTSD
Cornell University psychiatrists are carrying out tests using beta-blockers, the journal Nature reports.
The drug has been shown to interfere with the way the brain stores memories.
Post-traumatic stress disorder affects around one in three of people caught up in such events, and memories can be triggered just by a sound or smell.
People with PTSD are given counselling, but because it is not always effective, researchers have been looking for alternative therapies.
However there are concerns that a drug which can alter memories could be misused, perhaps by the military who may want soldiers to become desensitised to violence.
Fear and memory linked
The beta-blocker propranolol has been found to block the neurotransmitters involved in laying down memories.
Studies have shown that rats who have learned to fear a tone followed by an electric shock lose that fear if propranolol is administered after the tone starts.
The Cornell University team are reported to be seeing similar results in early studies in humans, Nature reports.
Margaret Altemus, who is one of the psychiatrists working on the study, told the journal: "The memory of the event is associated with the fear, and they always occur together."
The researchers plan to recruit 60 patients for a clinical trial where participants would be asked to take a dose of propranolol whenever they experienced symptoms of PTSD, such as an increased heart rate or breathing difficulties.
But so far only one person has volunteered to take part.
Dr Altemus believes patients can be reluctant to try new therapies.
She said a drug treatment could be a useful option for those with PTSD.
"People with PTSD are disabled - their communication and relationships can be crippled.
"It's a serious illness."
But other psychiatrists have expressed concern about the use of the beta-blocker in PTSD treatment.
Berthold Gersons, based at the University of Amsterdam in the Netherlands, said: "We hope it will work, but it is a simple solution."
He cautioned it may not work in all cases of PTSD.
But other experts say PTSD is a natural response to traumatic events and should not be treated with drugs.
Dr Paul McHugh, a psychiatrist at Johns Hopkins University in Baltimore, Maryland and member of the US President's Council on Bioethics expressed concern over the possible uses of the drug.
"If soldiers did something that ended up with children getting killed, do you want to give them beta blockers so that they can do it again?"
He added: "Psychiatrists are once again marching in where angels fear to tread."