Scientists believe they have found a way to dampen down the impact of bad memories in people's brains.
Bad memories can be difficult to endure
A US and Canadian team used a drug called propranolol to target unwanted memories, while leaving others intact.
They injected the drug, which is more often used to treat heart patients, while a volunteer was asked to recall a painful memory.
The Journal of Psychiatric Research study found that this seemed to disrupt the way the memory was then stored.
The researchers, from McGill University, in Montreal, and Harvard University in Boston, hope their work could lead to new treatments for patients with psychiatric disorders, such as post-traumatic stress.
However, others have warned the research is still at a very early stage - and expressed concern that it could potentially be abused easily.
The researchers treated 19 crash or rape victims for 10 days with a drug, or a placebo.
The volunteers were asked to recall their memories of a traumatic event that had happened 10 years earlier.
A week later the researchers found that those people who were given a shot of propranolol showed fewer signs of stress, such as raised heart rate, when recalling their trauma.
The researchers believe that memories are initially stored in the brain in a malleable, fluid state before becoming hard-wired into the circuitry.
Then, when they are recalled, they once again become fluid - and capable of being altered.
They believe propranolol disrupts the biochemical pathways that allow a memory to "harden" after it has been recalled.
More work needed
In a separate study, a New York University team said they had successfully erased a single memory from the brains of rats while leaving the rest of their memory intact.
Dr Monica Thompson, a consultant clinical psychologist at London's Traumatic Stress Clinic, stressed that post traumatic stress disorder was a complex condition with many other symptoms other than bad memories.
She said that even if a treatment successfully dampened down bad memories patients could still be left with potentially debilitating symptoms, such as high fear levels.
Professor Chris Brewin, of University College London, said the research was still at a very early stage, and much more work was needed to demonstrate that it could lead to tangible benefits.
"One also does not know what effect such a drug could have in the long term," he said.
"After all, fear reactions are there to protect people from danger in the future."