The longer you smoke pot and the earlier you start smoking it, the more likely you are to have problems recalling words in middle age.

But past exposure to marijuana doesn’t appear to affect other mental skills, such as processing speed and executive function.

So says a recent large study that tracked marijuana use in more than 3,000 people over 25 years. Participants came from a handful of cities.

“Cumulative lifetime exposure to marijuana remained significantly associated with worse verbal memory,” researchers wrote in the online medical journal, JAMA Internal Medicine.

The study comes at a time when more states are legalizing marijuana for medical purposes.

Though researchers did not examine the impact of smoking pot on overall memory, they did look at the effect on verbal memory. Notably, they found that when asked to memorize a list of 15 words, half of the people who smoked pot recreationally over time could recall about one word less than nonsmokers.

Participants were between 18 and 30 when the study started, and they were asked about their marijuana use at eight intervals throughout the 25 years.