"Although cannabis can have a negative impact on health, including mental health, in terms of relative harms it is considerably less harmful than alcohol or tobacco," says the report by the Beckley Foundation's Global Cannabis Commission.

"Historically there have only been two deaths worldwide attributed to cannabis, whereas alcohol and tobacco together are responsible for an estimated 150,000 deaths per annum in the UK alone."

"Many of the harms associated with cannabis use are the result of prohibition itself, particularly the social harms arising from arrest and imprisonment."

"Cannabis came under the control of the international narcotics treaties as an afterthought, in an era when use of the drug was confined to relatively small groups in a scattering of cultures."

"In the last half-century, the situation has been transformed."

"Smoking or other use of cannabis has become a part of youth culture in country after country."

"To serve this demand, huge international and national illicit markets have arisen."

"Strenuous efforts to enforce prohibition by policing and by quasi-military operations against illicit growing and sale have largely failed in their principal objective."

"Meanwhile, the efforts in themselves create substantial anguish and social harms."

"In the United States, about three-quarters of a million citizens are arrested every year for cannabis possession, and arrest figures are also high elsewhere."

The report then goes on to say that the only solution to the problems caused by prohbition is to regulate the sale of cannabis.

"It is only through a regulated market that we can better protect young people from the ever more potent forms of dope," it says.

"In an alternative system of regulated availability, market controls such as taxation, minimum age requirements, labelling and potency limits are available to minimise the harms associated with cannabis use."

The report will be submitted to the United Nations Strategic Drug Policy Review next year.