orig jr brain on weed
Your brain on marijuana
01:39 - Source: CNN
CNN  — 

Around the world tens of millions of people use cannabis.

It’s legal for recreational use in 11 US states and Canada. In these and some other places, it’s also approved to treat some medical conditions.

But a new analysis highlights that the debate over marijuana’s health risks and benefits is complicated and depends on the active compounds involved.

A review of existing research published Tuesday found that a single dose of the main psychoactive ingredient (THC) in cannabis – equal to one joint – in otherwise healthy people, can temporarily induce psychiatric symptoms, including those associated with schizophrenia.

“The first takeaway is that for people in general there is a risk, even if you are healthy and taking a single dose, a one-off, you could have these symptoms,” said Oliver Howes, a senior author on the study and molecular psychiatry professor at King’s College London’s Institute of Psychiatry, Psychology & Neuroscience.

The symptoms “are distressing and could affect your thinking. It’s not just something that’s going to affect people with a history of mental health problems,” he added, noting that having symptoms didn’t cause them to have a psychiatric illness.”

“They are distressing and could affect your thinking. You might not behave in a safe or rational way. It’s not just something that’s going to affect people with a history of mental health problems,” he added, noting that having symptoms didn’t cause them to have a psychiatric illness.

However, the analysis, published in the journal Lancet Psychiatry, found no evidence that cannabidiol (CBD), a non-psychoactive compound in weed that’s used in some medicinal cannabis and other products, does induce psychiatric symptoms. Howe said this was “reassuring” but noted that the available evidence was fairly limited.

While they are similar compounds and both found in cannabis, THC (tetrahydrocannabinol) and CBD don’t have the same effects. The THC is what you makes you feel “high,” while CBD is thought to have benefits without producing the same euphoric feeling.

Howes said that regulators, policy makers and health official needed to take into account the potential risk when considering the medical use of THC-containing products or allowing them to be used recreationally.

“As the THC-to-CBD ratio of street cannabis continues to increase, it is important to clarify whether these compounds can cause psychotic symptoms,” he said.

The psychiatric symptoms included paranoia, says Howes, including people thinking others were talking about them or threatening them in some way and hallucinations like hearing voices.

“There are also some people who become withdrawn and lose motivation. And whilst those are less dramatic, they could affect ability to work or drive a car. When you take a one-off dose, they [the effects] are temporary and last a few hours, but if you take it regularly, it could be an enduring consequence.”


In the review of available evidence, Howe and the other authors systematically examined 15 studies that took place in clinical settings involving 331 people with no history of psychotic or other major psychiatric disorders.

Howe said one strength of the review was that it focused on the effects of cannabis on healthy adults who didn’t have risk factors for psychiatric problems.

“This allows us to really test whether these cannabis components themselves lead to psychiatric symptoms,” Howe said.

While previous research has found a link between cannabis use and psychiatric symptoms, it’s not been clear whet