You can always tell someone who has been smoking weed for any length of time because they are just that little bit slower in the way they respond.
Only a fraction of a second in most cases but enough of a delay to alert us that we are dealing with someone who has lost a few braincells through a certain kind of herbal cigarettes.
New research has now borne it out that using marijuana may be related to certain changes in the brain related to a smaller volume of grey matter.
'We found that there is not only is a change in structure, but there also tends to be a change reflected in the connectivity' said study author Francesca Filbey, an associate professor in the School of Behavioural and Brain Sciences at the University of Texas at Dallas who explained that the connectivity could be compensation for the loss of grey matter
'All we can say is that we do see these differences in people who use marijuana, Filbey said explaining that 'We also saw that the younger you are when you start using marijuana regularly, the greater the changes in the brain'.
Of course it is not 100% reliable to surmise that the person you are talking to is a bit slower on the uptake due to marijuana smoking which has reduced their brain volume, they just may be a Sun reader or a UKIP voter who have naturally reduced brains anyway.