Long-term cannabis use leads to cognitive deficits, smaller hippocampal volume in midlife

Long-term use of cannabis tends to result in cognitive deficits and smaller hippocampal volume in midlife, according to a recent study.

“This study tested the hypotheses that long-term cannabis use is associated with cognitive deficits and smaller hippocampal volume in midlife, which is important because midlife cognitive deficits and smaller hippocampal volume are risk factors for dementia,” the authors said.

Participants were composed of members of a representative cohort of 1,037 individuals born in Dunedin, New Zealand, in 1972‒1973 and followed until age 45 years, with a retention rate of 45 percent. The authors assessed cannabis use and dependence at ages 18, 21, 26, 32, 38, and 45 years; IQ at ages 7, 9, 11, and 45 years; and specific neuropsychological functions and hippocampal volume at age 45 years.

Long-term cannabis users had a decline in IQ from childhood to midlife (mean ‒5.5 points), poorer learning and processing speed compared to their childhood IQ, and informant-reported memory and attention problems.

Such deficits were specific to long-term users only and were either not present or smaller among long-term tobacco users, long-term alcohol users, midlife recreational cannabis users, and cannabis quitters.

Of note, cognitive deficits among long-term cannabis users could not be explained by any of the following: persistent tobacco, alcohol, or other illicit drug use, childhood socioeconomic status, low childhood self-control, or family history of substance dependence.

Hippocampal volume was also smaller among long-term cannabis users. However, smaller hippocampal volume did not statistically facilitate cannabis-related cognitive deficits.

“Research is needed to ascertain whether long-term cannabis users show elevated rates of dementia in later life,” the authors said.