Dose-related neurocognitive effects of marijuana use

TLDR

Although about 7 million U.S. residents use marijuana weekly, little is known about persistent neurocognitive effects, and it is unclear whether deficits resolve or worsen with continued abstinence. To determine whether neurocognitive deficits persist after 28‑day abstinence and whether they are dose‑related to weekly joint consumption. A battery of neurocognitive tests was administered to 28‑day abstinent heavy marijuana users.

Abstract

<b><i>Background:</i></b> Although about 7 million people in the US population use marijuana at least weekly, there is a paucity of scientific data on persistent neurocognitive effects of marijuana use. <b><i>Objective:</i></b> To determine if neurocognitive deficits persist in 28-day abstinent heavy marijuana users and if these deficits are dose-related to the number of marijuana joints smoked per week. <b><i>Methods:</i></b> A battery of neurocognitive tests was given to 28-day abstinent heavy marijuana abusers. <b><i>Results:</i></b> As joints smoked per week increased, performance decreased on tests measuring memory, executive functioning, psychomotor speed, and manual dexterity. When dividing the group into light, middle, and heavy user groups, the heavy group performed significantly below the light group on 5 of 35 measures and the size of the effect ranged from 3.00 to 4.20 SD units. Duration of use had little effect on neurocognitive performance. <b><i>Conclusions:</i></b> Very heavy use of marijuana is associated with persistent decrements in neurocognitive performance even after 28 days of abstinence. It is unclear if these decrements will resolve with continued abstinence or become progressively worse with continued heavy marijuana use.