Two studies we have been working on have investigated the claim that cannabis leads to reduced motivation. We found that when you give people the equivalent of one spliff's worth of cannabis, under controlled conditions in a laboratory, they are less willing to work for money.

In other words, they are not as motivated as usual. However, we also compared people who are addicted to cannabis with a control group (non-cannabis drug users). We found that when neither group had used drugs for at least 12 hours, they did not differ in their motivation for money.

Our results suggest that when you have recently smoked cannabis, it reduces your motivation in the short-term. On the other hand, long-term cannabis use may not impair your motivation, as long as you stop smoking it for at least 12 hours.

'Amotivational syndrome'

In the late 1950s and 1960s, as cannabis became a popular recreational drug, academic reports of cannabis's 'amotivational syndrome' appeared. Clinicians stated that "regular marihuana [sic] use may contribute to the development of more passive, inward turning, amotivational personality characteristics".

However, these reports simply relied on observations of cannabis users and their lazy behaviour. Research was needed to investigate the short and long-term effects of cannabis.

Early research into the short-term effects of cannabis on motivation surprisingly found both motivating and demotivating effects of cannabis. Having said that, these studies were poorly controlled and sometimes rather bizarre in their design; one involved getting people stoned and asking them to make stools as quickly as possible.

A more recent study gave cannabis to people in a placebo-controlled experiment and reported reduced motivation for money. However, this experiment used a very small sample of five participants.

Our new study used a double-blind, placebo-controlled design to examine the effects of cannabis on motivation for money in a larger sample of 17 participants.

Through a balloon, participants inhaled cannabis vapour on one occasion and a placebo cannabis vapour on a separate occasion. Straight after, they completed a task designed to measure their motivation for earning money.

This was a real-life task as the participants were given money they had earned at the end of the experiment. In each trial, they could decide whether to complete low or high-effort options to win varying sums of money.

The low-effort option involved pressing the spacebar key 30 times in 7 seconds to win 50p (US$0.60). The high-effort option involved 100 space bar presses in 21 seconds for rewards varying from 80p (US$1.06) to £2 (US$2.66).

We found that people on cannabis were significantly less likely to choose the high-effort option. On average, volunteers on placebo chose the high-effort option 50 percent of the time for a £2 reward, whereas volunteers on cannabis only chose the high-effort option 42 percent of the time.

In other words, they had reduced motivation for the money available when they were stoned. Although it has been a long-held belief that getting high makes you lazy, this is the first time it has been reliably demonstrated using a suitable sample size.

No difference

The question of whether long-term cannabis use makes people demotivated, even when they're not high, is a more difficult one to answer. We cannot carry out randomised controlled trials in which some people are given cannabis for ten years while another group receive placebo for 10 years. That would, of course, be unethical.

Therefore, we have to rely on observational studies, where we look at associations between natural cannabis consumption and motivation levels. Some previous research has failed to find a link between cannabis use and altered motivation, although in one study earlier cannabis consumption predicted later anhedonia (difficulty experiencing pleasure).

In our observational study (that is, one that does not have an experimental manipulation), we compared 20 people who were addicted to cannabis against a control group of 20 people who were not addicted to cannabis. The control group used other drugs, including MDMA and cocaine, a similar amount to the cannabis group.

These participants completed the same motivation task as in the previous study after they had been clean of all drugs (apart from tobacco and caffeine) for at least 12 hours. We found no difference between the groups in their willingness to work for money. This suggests that long-term cannabis use may not reduce motivation after 12 hours of abstinence from the drug.

However, there are some important limitations with this study. Firstly, the sample sizes were small. Secondly, the study was cross-sectional, so we only investigated the participants at one point in time.

An improved study would have used a longitudinal design, in which people's motivation and cannabis use are measured at different time points as they grow up. This would have allowed for a better understanding of how cannabis consumption affects future motivation. Longitudinal research is needed to draw stronger conclusions.

What do our results mean to the average cannabis user? After years of being told that getting high makes you lazier, we've provided some of the first solid evidence that it's true.

Importantly though, it doesn't eradicate your motivation altogether - it makes you slightly, yet significantly, more apathetic. On the bright side, your long-term cannabis use may not erode your drive like some people claim, so long as you can put your joint down for a while.

The Conversation

Will Lawn, Post-doctoral researcher, UCL.

This article was originally published by The Conversation. Read the original article.