The barrier has been a major problem for doctors treating brain conditions like depression as it contains proteins which push the drugs out as soon as they get in. It has been shown that nine out of 10 compounds can't penetrate the brain.
But, a team at the University of Copenhagen found that compounds from the South African flowers Crinum and Cyrtanthus were able to pass through the barrier.
These could eventually be used to help deliver drugs to the brain, said Prof Birger Brodin, who led the research
"Several of our plant compounds can probably be smuggled past the brain's effective barrier proteins," he was quoted as saying by the Daily Mail.
"We examined various compounds for their influence on the transporter proteins in the brain. Our results are promising, and several of the chemical compounds studied should therefore be tested further, as candidates for long-term drug development," he said.
"The blood vessels of the brain are impenetrable for most compounds, one reason being the very active transporter proteins. So it is of great interest to find compounds that manage to 'trick' this line of defence," he noted.
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"Studies of natural therapies are a valuable source of inspiration, giving us knowledge that can also be used in other contexts," he added.
However, Pro Brodin warned that the study was only the first stage, and it would be a long time before the compound could be developed into useable drugs.
The new findings are detailed in the Journal of Pharmacy and Pharmacology.