Smoking cannabis not as harmful to the lungs as cigarettes – but can still trigger psychosis

Smoking cannabis was not found to damage the lungs, however scientists warn it still carries the risk of triggering psychosis

Smoking cannabis was not found to damage the lungs at low quantities, however scientists warn it still carries the risk of triggering psychosis

Smoking cannabis is less harmful to users’ lungs than exposure to tobacco, even though the two substances contain many of the same components, according to a new study.

The study led by the University of California San Francisco and University of Alabama at Birmingham, collected data from more than 5,000 U.S adults for more than 20 years.

'We found exactly what we thought we
would find in relation to tobacco exposure: a consistent loss of lung
function with increasing exposure,' said the paper’s lead author, Dr Mark
Pletcher at UCSF.

'We were, however, surprised that we found such a
different pattern of association with marijuana exposure.'

Smoking cigarettes can cause significant lung damage, including respiratory symptoms, chronic obstructive pulmonary disease and lung cancer.

It accounts for an estimated 443,000 deaths, or nearly one in every five deaths, each year in the United States, according to the U.S. Centers for Disease Control and Prevention.

However, data for the long-term effects of cannabis use on the pulmonary system has been scarce until now.

In a paper published today in the Journal of American Medical Association (JAMA), researchers measured the air flow rate and lung volume of just over 5,000 healthy adults aged 18 to 30.

When smoking cigarettes, study co-author Dr Stefan Kertesz said: 'There’s a straight-line relationship: the more you use, the more you lose.'

However, the same was not true with cannabis users. Air flow rate increased rather than decreased with increased exposure to cannabis up to a certain level.

'An important factor that helps explain the difference in effects from these two substances is the amount of each that is typically smoked,' Dr Pletcher said.

'Tobacco users typically smoke ten to 20 cigarettes/day, and some smoke much more than that. Marijuana users, on average, smoke only two to three times a month, so the typical exposure to marijuana is much lower than for tobacco.'

However, frequent cannabis use has been associated with anxiety, schizophrenia,
bipolar disorders and depression. It has also been found to affect learning for weeks after exposure.

'Marijuana is complicated,' Dr Kertesz told

'It could be affecting your social life, your work life or even your tendency to get into accidents.'

Cannabis is
classed as a sedating and hallucinogenic drug. Some users find it makes
them feel relaxed and happy in the short term. However, the drug can cause feelings of anxiety, suspicion, panic and paranoia. It can also increase the risk of developing psychosis.

It is a Class B drug in the UK, which means it is illegal to possess or supply.