Is weed good for you? Everything we know about the health effects of cannabis

By Emanuela Campanella


It’s official. Prime Minister Justin Trudeau has announced that recreational pot legalization will come Oct. 17. The law has been passed and provinces and cities throughout the country are preparing for the big day. But how are Canadians prepping? Now that the substance will be readily available to the public, the health debate is back on the table.

The health effects of cannabis have been a polarizing debate for the last century and it’s only in the last couple of decades that the substance has been legally used for medicinal purposes.


“This is still a new age type of medicine despite it being a historical plant we used for many years,” Micheal Verbora said, an assistant professor at McMaster University.

“This has been a drug and it has been prohibited to be studied. So if you look at the literature, there is a bias. Ninety per cent of the research that has been up to date, the primary outcomes in those studies are looking for harms,” Verbora added, who is also the medical director of Canabo Medical Clinic.

Cannabis contains cannabidiol, or CBD, a chemical thought to be responsible for many of marijuana’s therapeutic effects. It is the compound in medicinal marijuana used for treating chronic pain, inflammation, epilepsy, nausea and anxiety, among other things.

“So CBD is cannabidiol. It’s like the yin to the yang of THC. It’s being studied for a number of different conditions. It’s quite a promising medicinal ingredient. But it does not have any recreational value.”
It is important to make the distinction between this compound and THC, which is what gets you high and is sometimes connected to the harmful aspects of weed.

The thing is, since the substance has been illegal for so long, the health industry hasn’t really invested in long-term health studies. So we truly don’t understand its long-term impact.

But a massive report by the National Academies of Sciences, Engineering, and Medicine gives one of the most comprehensive looks — and certainly the most up to date — at exactly what we know about the science of cannabis as a whole.

The committee behind the report considered more than 10,000 studies published since 1999 for its analysis and reached nearly 100 conclusions.


Marijuana use affects the lungs but doesn’t seem to increase the risk of lung cancer. But there may be a link between smoking pot, bronchitis and chronic coughs.

“Typically, cannabis in the past has been consumed through combustion methods such as smoking. The reality is when you heat a product up past 400 F (200 C), you get toxic by-products such as benzene, and benzene can go into the body and cause carcinogenic effects.”

Researchers also said that more research is needed to determine whether and how cannabis use is associated with heart attack, stroke and diabetes. But some evidence suggests that pot smoking may play a role in triggering a heart attack. 

Within a few minutes of inhaling marijuana, your heart rate can increase between 20 and 50 beats a minute, according to the U.S. National Institute on Drug Abuse.

On the mental-health front, evidence reviewed suggests that pot use may increase the risk of developing schizophrenia and other psychoses.

“When you consume too much and you start to lose insight or awareness as to what is going on, it can lead to many medical complications or issues. The biggest one is psychosis. The overall risk is still quite low. Some of the research out there shows 1 in 20,000 people can have a psychotic episode from the use of cannabis,” Verbora said.

Cannabis use was also linked to a small increased risk of depression but it doesn’t seem to be a gateway for hard drugs, as some opponents argue.

To no surprise, the report also found that learning, memory and attention are impaired immediately after getting high. But there was limited evidence showing a connection between cannabis use and lower academic achievement.


How about smoking cannabis during pregnancy? Some evidence suggests that there is a link to lower birth weight. But there is a lack of medical research out there to truly understand other pregnancy and childhood outcomes from cannabis use.

In general, there are still many questions about how marijuana affects the body and brain, and scientists say far more research is needed.

But if you’re going to use pot, what is the safest way of doing it? Verbora recommends keeping THC levels down and eliminating the toxins that come from smoking pot.

“One could recommend vaporizing or ingestion and those two methods will produce the least amount of harm because smoking is the toxic method of consumption, Verbora said.

“Vaporizing will not create those toxic ingredients. It would give someone an effect that would be short-term. So if you’re going to consume cannabis, you should start low and that should be five milligrams of THC or less. And you should wait six to eight hours to see what effects you had.”

With recreational pot scheduled to be legalized on Oct. 17, Verbora predicts more people will be using it, at least at the beginning.

But he says people should remain cautious: we don’t know much about weed’s long-term health effects. However, with its wide availability, there will likely be more investment in health studies to evaluate the impact pot may have on our health.