Nearly half of cannabis users in US states where the drug has been legalised have gone to work stoned, according to a survey.

Some 48% of the 600 pot smokers responding to an Instamotor survey said they had gone to work under the influence of the psychoactive plant.

Half of them admitted they would likely be fired of their bosses found out but that had not prevented them from taking the edge off before a shift.

Some 39% said they went to work high every week.

"Even if recreational marijuana is legal in your state employers can still drug test you and can choose to maintain a drug and alcohol free environment," the report's authors said.

"This means marijuana in your system can still exclude you from potential job opportunities or cause you to be terminated from your current job."

The poll would not stand up to scientific scrutiny. However, it paints an anecdotal picture of the way cannabis users regard the drug as being non detrimental to their faculties.

Indeed, 73% of respondents said they performed better at work if they were under the influence.

In a previous survey by Instamotor – an online car marketplace – 39% of cannabis users reported being confident to drive safely after consuming the drug.

"Despite our previous study illuminating that many marijuana users feel comfortable driving under the influence of marijuana, it's still illegal," the authors wrote.

"Though there isn't yet a definitive marijuana limit or the equivalent of Blood Alcohol Content, you can still be charged with driving under the influence. So if you're headed to work high, take the bus."

marijuana
A man rolls a joint during a demonstration Pedro Pardo/ AFP

An increasing number of US states have legalised cannabis for medicinal use in recent years – some have even started to permit its sale to recreational smokers. In the UK, the drug remains outlawed, although former government drugs chief Professor David Nutt has called for the benefits of medical cannabis to be recognised.

Writing for the Mail on Sunday, he said: "The American Academy of Science last year published a comprehensive report revealing the medicinal value of cannabis across a range of diseases including cancer and Aids, PTSD and addictions, cardiovascular and gut diseases.

"At least 17 countries other than America have medical cannabis at present, including Holland and Spain. For the UK, once a world-leading country in healthcare, to deny the value of medical cannabis is a sad reflection on how much political polemic has distorted rational thinking."