No difference found in negotiating obstacle course when clean or after three joints, say researchers

A new study says that smoking a joint - or three - of cannabis does not affect the ability of regular users of the drug to ride a bicycle.

Led by Dr Benno Hartung of the University Clinic in Düsseldorf, researchers had the 14 participants in the study – 12 men and two women – ride around an obstacle course.

Each undertook a number of rides on the course, the first sober, the others after smoking one, two or three joints, reports the Smell the Truth blog on the San Francisco Chronicle's SF Gate website.

For each puff of the joint, they were required to inhale for four seconds then hold their breath for a further 10 seconds.

They had points deducted for riding errors such as ignoring red traffic signals, hitting obstacles and going off course, enabling researchers to draw up a score for each run.

 The study, published in the International Journal of Legal Medicine, concluded: “Hardly any coordinative disturbances could be detected under the influence of high or very high THC concentrations.

“Only a few driving faults were observed even under the influence of very high THC concentrations … On average, there is no increase in the number of demerits after the cannabis consumption.”

However, the study’s authors underlined that participants were regular cannabis users and that the research suggested habitual users have a different response to THC than those who do not use the drug.

 “A defined THC concentration that leads to an inability to ride a bicycle cannot be presented,” they said.

“The test subjects showed only slight distinctive features that can be documented using a medical test routinely run for persons under suspicion of driving under the influence of alcohol or drugs.”

Last May we reported on two other studies led by Dr Hartung that assessed the ability of people to ride a bike while under impaired – one when drunk, the other while hungover.

> Study: Men safer in the saddle than women when extremely drunk

> Riding the morning after: How safe is hungover cycling?


Born in Scotland, Simon moved to London aged seven and now lives in the Oxfordshire Cotswolds with his miniature schnauzer, Elodie. He fell in love with cycling one Saturday morning in 1994 while living in Italy when Milan-San Remo went past his front door. A daily cycle commuter in London back before riding to work started to boom, he's been news editor at road.cc since 2009. Handily for work, he speaks French and Italian. He doesn't get to ride his Colnago as often as he'd like, and freely admits he's much more adept at cooking than fettling with bikes.