Long-term cannabis users have lasting memory and attention deficits

Price, Dr Cathy
Fried, Dr Peter

Consultant in Pain Management; Denmead, UK (Price)
Carleton University; Ottawa, Canada (Fried)

Abstracted from:Solowij N, Stephens R, Roffman R, Babor T, Kadden R, Miller M, Christiansen K, McRee B, Vendetti J, for the Marijuana Treatment Project Research Group. Cognitive functioning of long-term heavy cannabis users seeking treatment. JAMA 2002; 287: 1123-1131 .

Evidence-based Healthcare 6(3):p 109-110, September 2002.

BACKGROUND

There are continuing debates about decriminalising marijuana and about allowing its use for medicinal purposes. More than seven million people in the United States report weekly cannabis use. It is unknown whether the cognitive impairments associated with long-term cannabis use continue after people stop taking the drug.

OBJECTIVE

To examine the duration of cannabis-related effects on cognitive function.

SETTING

Washington, Connecticut, Florida; 1997 to 2000.

METHOD

Multicentre before-and-after study.

PARTICIPANTS

One hundred and two people seeking treatment for cannabis dependence (near daily consumption) and 33 controls. People were excluded if they had a psychotic disorder; other drug or alcohol dependence; poor language skills, or serious illness or injury which could have affected the brain.

ANALYSIS

Outcomes were assessed prior to a treatment programme and following an abstinence period (mean 17 hour duration). Long-term users (24 years mean use) and shorter-term users (mean 10 years use) were compared.

OUTCOMES

Attention, memory and executive functioning measured with neuropsychological tests.

MAIN RESULTS

Long-term users had reduced attention and memory function compared to shorter-term (p = 0.001) and non-users (p = 0.005). Long- and shorter-term users also had poorer time-estimation skills than controls (p < 0.001). Cognitive performance was inversely correlated with the length of cannabis use.

AUTHORS' CONCLUSIONS

Long-term heavy cannabis users have impaired memory and attention. These impairments continue beyond the period of intoxication and worsen with length of use.

NOTES

The findings are based on retrospective analysis of paid participants. The division of 'long' and 'shorter-term' users is somewhat arbitrary. The definition of 'shorter-term' use could be questioned given that this group had been users for an average of 10 years. The abstinence period was short and the study may be underpowered.