Long-term marijuana use tied to worse verbal memory in middle age

Long-term marijuana use tied to worse verbal memory in middle age | Reuters
As marijuana becomes more accessible to young and old alike in the U.S., researchers warn that long-term use of the drug may cause lasting harm to at least one type of brain function.
A new study based on following thousands of young adults into middle age finds that long-term marijuana use is linked to poorer performance on verbal memory tests, but other areas of brain function do not appear to be affected.
...Auer and colleagues analyzed data from a 25-year U.S. study of young adults, which included repeated measures of marijuana exposure over time and a standardized test of verbal memory, processing speed and executive function in year 25.
Almost 3,500 participants completed the standardized tests.
At the beginning of the study period in the 1980s, participants were 18 to 30 years old and more than 80 percent reported past marijuana use.
Just 12 percent continued to use marijuana into middle age, according to the results in JAMA Internal Medicine.
Researchers found that as past years of marijuana use increased, verbal memory scores decreased. 
In practical terms, the results meant that for every additional five years of exposure, 50 percent of marijuana users would remember one less word from a list of 15 tested words.