Second-hand exposure to marijuana smoking may damage blood vessel function, scientists have found out. The study suggests it might be necessary to implement measures to regulate marijuana smoking in places it has been legalised, just like tobacco smoking.

There is high public awareness that smoking tobacco can impact people standing nearby – passive smokers who can also end up suffering from health problems, cardiovascular in particular.

However, most people believe marijuana is less harmful. It is true that few studies have come up so far with evidence that marijuana second-hand smoking can cause acute cardiovascular harm.

But given the chemical and physical similarity between marijuana and tobacco smoke, the scientists believed investigating this further was necessary.

Their study, published in the Journal of the American Heart Association, is based on animal-models, but it provides a clear case that marijuana smoke can harm blood vessels, even after a short exposure and even if individuals are just 'passive smokers'.

Rat smokers

The scientists used rats to perform their experiments. They exposed the animals to marijuana smoke, as if they were passive-smokers, during one minute. They also carried out similar experiences with tobacco, to have a point of comparison.

"Arteries of rats and humans are similar in how they respond to secondhand tobacco smoke, so the response of rat arteries to secondhand marijuana smoke is likely to reflect how human arteries might respond," senior author Matthew Springer points out.

With his team, he assessed blood vessel function – how efficiently blood flowed through the arteries – before and after the exposure. The scientists discovered that when rats inhaled secondhand marijuana smoke for only a minute, their arteries carried blood less efficiently for at least 90 minutes, whereas similar exposure to secondhand tobacco smoke caused blood vessel impairment that recovered within 30 minutes.

The researchers believe it is the mere burning of the plant material that appears responsible for the impaired blood vessels, not chemicals like nicotine and tetrahydrocannabinol (THC), the psychoactive ingredient in marijuana.

This study makes the case that with an increasing number of states legalising medicinal and recreational marijuana in the US, along with increasing potential for corporate expansion within the cannabis industry, it is crucial to understand the health consequences of second-hand marijuana smoke exposure. More research should thus be conducted soon to assess the consequences of second-hand marijuana smoking in greater depths.