According to a leading U.S. expert, cannabis smoke is less likely to cause cancer than tobacco smoke.
Dr Robert Melamede, of the University of Colorado, says that although chemically similar, tobacco was more carcinogenic.
Apparently the difference is mainly due to the nicotine in tobacco, whereas cannabis possibly inhibits cancer because of the presence of the chemical Tetrahydrocannabinol (THC).
Health campaigners have however been quick off the mark and are warning against complacency.
According to the British Crime Survey, cannabis remains the most commonly-used drug in the UK with one in 10 people using it in the last year.
Smoke from tobacco and cannabis contains many of the same carcinogens, and cell damage linked to lung cancer has been found in the lungs of chronic cannabis smokers.
The class C drug, which was downgraded in 2004, and has previously been linked to mental health problems and breathing difficulties.
Scientists have however been exploring whether it can be used to treat a range of conditions, including multiple sclerosis and Alzheimer's disease.
Dr Melamede said whereas nicotine activated carcinogenic compounds, THC, one of 60 cannabinoids derived from the cannabis plant, had been shown to inhibit these dangerous compounds in mice cells.
Melamede says that compounds found in cannabis have been shown to kill numerous cancer types including lung, breast, prostate, leukaemia, lymphoma and skin cancer.
But he said the effects of cannabis were complex as some evidence has also suggested low doses of THC could stimulate growth of lung cancer cells.
He also says that the two could interact as cannabis was often smoked with tobacco, and the possibility exists that as the cannabis-consuming population ages, the long-term consequences of smoking cannabis may become more similar to what is observed with tobacco.
Current knowledge does not, he says, suggest that cannabis smoke will have the carcinogenic potential resulting from exposure to tobacco smoke.
According to Jean King, director of tobacco control at Cancer Research UK, many of the studies that had looked at the link between cancer and cannabis had used purified cannabinoids, and the results from such studies may not be representative of the overall effects of cannabis smoke, which contains more than 400 chemicals.