The discovery reported in the journal Nature Neuroscience could help treat some anxiety disorders and phobias.
In the study, a fearful memory was created by associating pictures of spiders with an electric shock to the wrist. Volunteers were then split a day later and some received a beta-blocker.
Researchers say those on the medication had less fear when they were once again shown the spider pictures.
It's thought beta-blockers can interfere with how the brain makes sense of frightening events.