New research suggests a single joint of cannabis damages the lungs as much as smoking five cigarettes in one go.

The study, carried out by the Medical Research Institute of New Zealand, found the drug forces the lungs to work harder by obstructing air flow and causes chest tightness and wheezing.

The study found that of the 339 people tested, only those who smoked tobacco suffered from the lung disease emphysema, but cannabis use still stopped the lungs working properly.

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Using marijuana increases the risk of one day developing a psychotic illness such as schizophrenia, according to a study that provides some of the strongest evidence yet linking the drug to a mental disorder.

Marijuana is one the most commonly used illegal substances in many countries with up to 20 percent of young people in places like Britain reporting either some use or heavy use, British researchers said, citing government statistics.