The idea that smoking pot is less dangerous than the use of heroin or drinking alcohol, and less addictive, has been definitively debunked by a World Health Organization expert, but some media are reporting the reports are false.

Professor Wayne Hall, a drugs adviser to the World Health Organization and professor on addiction policy at King's College London, released the results of a 20-year study proving the point, The Daily Mail reported.

He said, in the paper, that cannabis is highly addictive, causes mental health problems and opens the door to harder drugs.

"If cannabis is not addictive then neither is heroin or alcohol," Hall told The Daily Mail. "It is often harder to get people who are dependent on cannabis through withdrawal than for heroin -- we just don't know how to do it."

The drug was seen to have an especially negative effect on teens, showing that it affected their development and academics.

One in six teenagers who regularly smoke the drug become dependent on it, and users do worse at school since heavy use in adolescence appears to impair intellectual development, IOLifestyle reported.

Similarly, one in 10 adults regularly smoking weed become dependent and are more likely to go on to using harder drugs.

In addition to being highly addictive, it doubles a user's risk of developing psychotic disorders, including schizophrenia, and smoking before driving impairs judgment and increases the risk of a crash.

But despite these conclusions reported in some media, the Washington Post reported that the claims made in the paper are not what has been reported and is not a scientific study but instead addresses observations over a 20-year period.

The paper doesn't reveal anything new and has focused on the long-term effects of daily or regular use, the Washington Post reported.

In fact, those are the key points of the study, which included some of the points reported by other media.

The similar points highlighted include not smoking while driving or pregnant and heavy use by teens increases their chance of not doing well academically and developing mental impairments.

Hall's paper actually reveals that marijuana is addictive, but no one can overdose from it.

Other points reported by the Washington Post include the various medical and psychological ailments that are linked to smoking pot, but there was no mention of debunking any unknown claims of marijuana use.