Endorsement of the relative safety of the recreational drug from a prestigious medical source will increase pressure on ministers to relax the legal ban on cannabis, which extends to its use for medicinal purposes.
This week a select committee of the House of Lords urged that prescription of cannabis, and its derivatives, by doctors should be permitted for some patients, such as those with multiple sclerosis, whom it has been shown to help.
The Government rejected the Lords' advice on the ground that clinical trials have not been done. It was backed by the British Medical Association, which said crude cannabis was not a suitable medicinal product because it contained toxic ingredients, including high levels of tar.
The Lancet says in an editorial that patients are entitled to advice on the likely dangers of cannabis use. These include the risk of accidents when intoxicated, irritation of the lungs, dependence with daily use and subtle cognitive impairment with long-term use.
However, compared to the damage wreaked by alcohol and tobacco, these dangers are not excessive.
"It would be reasonable to judge cannabis less of a threat to health than alcohol or tobacco, products that in many countries are not only tolerated and advertised but are also a useful source of tax revenue."
A separate review article in the journal quotes the National Drug and Alcohol Research Centre in Sydney, Australia, which says that most cannabis users stop in their mid to late 20s and few use it daily for years.
In the United States and Australia, about one in ten of those who use cannabis becomes a daily user and another two or three use the drug weekly.
In its editorial, the journal says the debate about whether cannabis should be legalised for recreational use is complicating scientific assessment of the therapeutic effects of cannabinoids, the drug's active constituents.
It states: "The desire to take mood-altering substances is an enduring feature of human societies worldwide and even the most draconian legislation has failed to extinguish this desire . . .
"This should be borne in mind by social legislators who, disapproving of other people's indulgences, seek to make them illegal. Such legislation does not get rid of the problem, it merely shifts it elsewhere."
It concludes: "On the medical evidence available, moderate indulgence in cannabis has little effect on health, and decisions to ban or to legalise cannabis should be based on other considerations."Reuse content