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1974: Cannabis 'causes brain damage'
New studies in America have revealed that smoking cannabis can cause brain damage.

The US government has funded the cultivation of marijuana in the southern United States for research purposes.

The drug was prepared and dried before being sent on to more than 50 medical schools and research centres to study its effects on animals and humans.

Researchers in New Orleans claim the active ingredient of cannabis, THC, has had severe detrimental effects on laboratory animals.

When you're stoned a problem can come up and it takes a while to get your stuff together
Vietnam war veteran marijuana addict
But supporters say cannabis is no more harmful or less harmful than drinking alcohol or smoking tobacco.

In a laboratory in New Orleans, rhesus monkeys were forced to smoke the equivalent of two cannabis cigarettes a day for nearly a year.

Electrodes implanted in their brains measured brain activity, and the results have indicated major if not permanent damage.

Researchers claim cannabis has a lasting impact - one monkey had not been subjected to the testing for six months, but still showed 'disrupted brain wave patterns'.

Studies on humans have assessed the effects of cannabis smoking on hormonal disruption, birth defects and severe personality disorders.

BBC correspondent John Humphreys spoke to two Vietnam War veterans taking part in the study who were heavy cannabis smokers of cannabis while on active duty.

"I just can't get my thoughts together quick enough. When you're stoned a problem can come up and it takes a while to get your stuff together to be able to deal with it. I'm still the same way now," said one.

Cannabis or marijuana is commonly used in the US - an estimated one in every eight Americans - 25 million people - have smoked the drug, and two million teenagers are regular users.

The drug is illegal in the United States for possession and consumption, and conviction for an offence often leads to a prison sentence.

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cannabis plant
Monkeys have shown 'disrupted brain wave patterns'

In Context
The most famous research from the time was carried out by a Dr. Robert Heath of Tulane University Medical School, New Orleans.

His findings of permanent brain damage have been dismissed by similar, independently conducted studies. But other scientists have argued these methods of animal research are inconclusive.

The debate continues to rage about the merits and perils of taking the drug. For example, some research argues cannabis aids multiple sclerosis sufferers, while other findings indicate cannabis increases the risk of psychosis and is more carcinogenic than tobacco.

One in three adult Americans now admit to having smoked the drug. In 2000, around 750,000 people were arrested on marijuana charges. The federal government spends billions of dollars enforcing its prohibition.

In the UK, cannabis possession remains a criminal offence, although it has been downgraded to a Class C drug.

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