But cannabis users were just as motivated as others when they weren’t under the influence.
Using marijuana makes people slightly less likely to work hard for money, according to a study said to be the first to scientifically confirm what generations of drug users and their friends knew already.
However the researchers found no difference between cannabis users not under the influence of the drug and non-users – at least when it came to a test that involved tapping their little finger really quickly.
Dr Will Lawn, another of the UCL researchers, admitted cannabis was “commonly thought to reduce motivation”.
But he added: “This is the first time it has been reliably tested and quantified using an appropriate sample size and methodology.
“It has also been proposed that long-term cannabis users might also have problems with motivation even when they are not high.
“However, we compared people dependent on cannabis to similar controls, when neither group was intoxicated, and did not find a difference in motivation.
“This tentatively suggests that long-term cannabis use may not result in residual motivation problems when people stop using it. However, longitudinal research is needed to provide more conclusive evidence.”