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Methylene blue has been used in medicine for more than a century, said Timothy Duong, the senior researcher on the study and a professor at the University of Texas Health Science Center at San Antonio.
These days, he said, it's used to manage a condition called methemoglobinemia, where the blood cannot deliver enough oxygen to the body's tissues. It's also used to treat poisoning by cyanide or carbon monoxide.
But evidence dating back to the 1970s suggests the drug may also enhance memory, in animals and humans, Duong said.
In the new study, his team found that a single dose of methylene blue improved memory test performances by 13 healthy adults in a small, placebo-based clinical trial. Based on MRI brain scans, the medication worked by stimulating brain structures involved in processing memories as well as visual and sensory information.
Methylene blue is readily available and cheap, Duong said. But at this point no one is suggesting it's ready to be used for preventing or treating memory decline.
"Clearly, this is early research," said Dr. Ezriel Kornel, an assistant clinical professor of neurological surgery at Weill Cornell Medical College in New York City.
For one, it's not known whether the drug's effects diminish over repeated doses, said Kornel, who wasn't involved in the study. What's more, he said, the study included only people with intact memories and not those with impairments.
Still, Kornel called the findings "fascinating." He said larger, longer-term studies should dig deeper into the drug's potential.
According to Duong, methylene blue acts as "an antioxidant and an energy enhancer." In simple terms, it can allow brain cells to receive more energy.
While there was already evidence that methylene blue can boost short-term memory, Duong said his team wanted to know how the drug affects the brain.
To do that, the researchers used functional MRI, which tracks blood flow in the brain as a person performs mental tasks.
The study group included 26 healthy men and women, ages 22 to 62. Each underwent fMRI before and one hour after receiving either a single low-dose methylene blue pill or a placebo (an inactive treatment).
Overall, the researchers found, people given the drug showed an increase in brain activity during their mental tasks. That included changes in brain areas related to emotional responses, memory, and the ability to process visual and sensory information.
The drug also improved test scores a bit. On average, people had a 7 percent increase in correct responses related to memory "retrieval."
"The next step is to see if this works in patients with memory problems," Duong said. "We have a similar study underway that includes people with mild cognitive impairment."
According to Kornel, the "beauty" of methylene blue is that side effects are "minimal" at low doses. He cautioned, however, that if the drug were to become widely used, new safety issues could crop up.
The findings were published online June 28 in the journal Radiology.
Copyright © 2016 HealthDay. All rights reserved.
SOURCES: Timothy Duong, Ph.D., University of Texas Health Science Center at San Antonio; Ezriel Kornel, M.D., assistant clinical professor, neurological surgery, Weill Cornell Medical College, New York City; June 28, 2016, Radiology online