As recent studies show conflicting findings about the effects of THC on cardiovascular health, it’s vital to look at the detail, says expert.
A study led by researchers at Stanford University recently concluded that THC – the psychoactive compound found in cannabis – causes inflammation in cells that line the blood vessels and thickening of the arteries (atherosclerosis). This could later lead to heart disease and heart attack, researchers said.
But research into the effects of cannabis on cardiovascular health has been mixed, with some papers finding THC actually offers a protective effect on the heart.
One study published in April this year, for example, produced results that contradicted the Stanford findings.
The study of laboratory rats, published in Frontiers in Bioscience-Landmark, found that THC acted as a cardioprotective by improving the metabolic activity of cells in the heart, decreasing cell damage and restoring heart mechanical function.
The conflicting reports highlight the need to weigh up the evidence and “look at the detail” when it comes to scientific studies, says neurologist and chair of the Medical Cannabis Clinicians Society and the Cannabis Industry Council, Professor Mike Barnes.
Increased risk of heart disease?
Although scientists in the first study found that THC has a “significantly adverse effect on the cardiovascular system”, the study also showed that inflammation and atherosclerosis could be “blocked” by a small molecule called genistein found naturally in soy and fava beans.
“As more states legalise the recreational use of marijuana, users need to be aware that it could have cardiovascular side effects,” said Joseph Wu, MD, PhD, professor of cardiovascular medicine and of radiology, and the director of the Stanford Cardiovascular Institute.
“But genistein works quite well to mitigate marijuana-induced damage of the endothelial vessels without blocking the effects marijuana has on the central nervous system, and it could be a way for medical marijuana users to protect themselves from a cardiovascular standpoint.”
The researchers used genetic and medical data sourced from UK Biobank to analyse roughly 500,000 people aged between 40 and 69.
Of these, nearly 35,000 participants reported smoking cannabis, with 11,000 smoking more than once a month. The Stanford scientists found that the latter were “significantly” more likely than others in the study to have a heart attack. The researchers also found that frequent smokers were more likely than non-users to have their first heart attack before the age of 50.
In an effort to find a potential antidote to the inflammation and atherosclerosis reportedly caused by THC, the scientists turned to the endocannabinoid system, a complex network of neurotransmitters and receptors. The two most important receptors are referred to as CB1 and CB2.
Using machine learning techniques, the researchers scanned a large database of protein structures to find a molecule that binds to the body’s CB1 receptor hence blocking THC’s inflammatory and atherosclerotic properties.
What they came up with was a molecule called genistein, which is naturally found in soybeans. The molecule binds to CB1, blocking the drug’s harmful effects without inhibiting the psychoactive effects of THC.
“We didn’t see any blocking of the normal painkilling or sedating effects of THC in the mice that contribute to marijuana’s potentially useful medicinal properties,” said instructor of medicine, Mark Chandy, MD, PhD.
“Genistein is potentially a safer drug than previous CB1 antagonists. It is already used as a nutritional supplement and 99% of it stays outside the brain, so it shouldn’t cause these particular adverse side effects.”
Mike Barnes, chair of the Cannabis Industry Council said that people “should not take this sort of publication seriously without looking at the detail”.
Referring to Stanford University’s reliance on data from the UK, Barnes said: “The big problem here is that in the UK and most of Europe smoking a joint normally means smoking a mixture of tobacco and cannabis. And we know tobacco, of course, is harmful to the heart and circulation.
“Thus, the fact that joint smokers have more heart problems in the UK does not mean that cannabis causes it. It could easily be, and probably is, the tobacco effect.
“Remember that smoking is illegal in the UK and not the way cannabis under prescription is taken. Vaping is much safer as the temperatures are lower.”
A protective effect?
The second study aimed to test whether THC may be protective in the treatment of cardiovascular dysfunction following ischemia-reperfusion injury, the damage caused when blood supply returns to tissue, following a period of ischemia or lack of oxygen.
Results from the animal study, conducted on rat hearts, showed that THC protected the heart, evidenced by the improved recovery of cardiac function.
The authors concluded: “THC promotes the viability of cardiomyocytes, improves their metabolic activity, decreases cell damage and restores heart mechanical function, serving as a cardioprotective. We proposed the use of THC as a cardioprotective drug to be, administered before onset of I/R [ischemia-reperfusion] protocol.”
Professor Barnes cautioned: “Many papers show a protective effect of most cannabinoids on the heart, although having said I would avoid prescribing cannabis within three months of a heart attack or stroke or in anyone who would not benefit from an increased heart rate which occurs with THC.”