22 July 2014
Heavy cannabis users and very anxious people both process attention in the same way and neither realise they are feeling anxious.

by Thomas Wilcockson

Cannabis users behave like very anxious people when we ask them to pay attention to things that might make someone anxious.

We already know that heavy cannabis users are likely to have anxiety and control their emotions less well than others. What we don’t know is whether cannabis is causing anxiety or anxiety causing cannabis use.

We are researching this link by using people’s biases in paying attention to different things.  When you first pay attention to something it grabs your attention.  Once you’ve started to pay attention, it can hold your attention. You can also avoid paying attention to something.

If you abuse a substance it can alter all these types of attention. If you are a heavy drinker, alcohol can grab your attention more than it does for other people. If you are seeking treatment for alcoholism, then you may avoid looking at alcohol.

We were interested to find out about what attention bias could tell us about why heavy cannabis users also tend to be anxious.

We can study what people are paying attention to – whether something grabs or holds their attention or whether they avoid it – by using eye movement cameras. Anxious people are more likely to avoid looking at threatening pictures than people who are not anxious, but there isn’t a difference for more neutral pictures.  We found that the same was true for people who use cannabis heavily – they also avoided looking at threatening pictures.

Recording volunteers' eye movements in the lab

This type of eye movement is usually unconscious and people who avoid looking at a picture in this way are not aware of avoiding it.  They also don’t consciously feel that they are anxious – when we asked both groups if they currently felt any anxiety symptoms, both groups said no.

From our study, we think that heavy cannabis users may feel unconsciously anxious, even if they do not feel consciously anxious. Cannabis may increase the risk of developing an anxiety problem; or being anxious already may lead people to self-medicate with cannabis; or both of these things could be happening. We don’t yet understand all the motivations underlying the link between the two, but we’d like to find out more.