Claims that cannabis is harmless have been disputed in a report that suggests the drug is becoming more powerful and could lead to long-term health damage.

The study, published in the British Journal of Psychiatry, warns that cannabis can provoke anxiety and mental illness, seriously impairs driving skills, is five times more damaging to the lungs than cigarettes, weakens the immune system and may lead to rare throat cancers or fatal heart attacks.

Heather Ashton of Newcastle University, UK explains that in the 1960s a typical 'joint' of cannabis contained 10 mg of delta-9 tetrahydrocannabinol (THC), compared to today when a joint may contain 150 — 300 mg. "Cannabis affects almost every body system. It combines many of the properties of alcohol, tranquillisers, opiates and hallucinogens," she stresses.

In a separate report in the same journal, Andrew Johns of the Maudsley Hospital, London emphasized the harmful effects...

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