Cannabis !

As medical and recreational use of marijuana continues to grow , a dangerous lack of awareness about its health risks could be putting millions of lives at risk. This is the conclusion reached by the British Lung Foundation (BLF), a leading charity that is worried about the "alarming disconnect" between the public perception of the drug as being relatively safe, and mounting evidence indicating that it dramatically increases a person's chance of developing cancer.

According to a report issued by the BLF, nearly 9 in 10 people believe that smoking cigarettes is worse than marijuana — but the risk of developing lung cancer is as much as 20 times greater from a cannabis joint than a tobacco cigarette. Researchers contend that smoking one marijuana joint is equivalent to smoking an entire pack of cigarettes.
The BLF report contradicts a study from earlier this year claiming that marijuana does not cause lung damage. Back in January of 2012, Stefan Kertesz, an associate professor in the UAB Division of Preventive Medicine, published a study claiming that occasional marijuana use was associated with increases in lung air flow rates and increases in lung capacity. His data showed that even up to moderately high-use levels — one joint a day for seven years — will not decrease air-flow rates or lung volumes.