University College. UK: New UCL-led
research reveals the positive and negative effects of different types of
cannabis on the human brain, in a trial broadcast on Channel 4: Drugs Live: Cannabis on Trial.
“Our cannabis research over the last
six years has highlighted how different types of cannabis can have different
effects,” explains Professor Val Curran, Director of the UCL Clinical
Psychopharmacology Unit, who led the study. “The cannabis plant contains around
100 unique ingredients called ‘cannabinoids’. The two most prominent of these
are THC (tetrahydrocannabinol) and CBD (cannabidiol). THC is the stuff that
makes you stoned. Our previous research suggests that CBD may be a kind of
antidote to some of the harmful effects of THC.”
In the study, the team compared the
effects of two different types of cannabis. One type has high levels of THC
(~13%) but virtually no CBD and is often referred to as ‘skunk’. The other
type, sometimes called ‘hash’, generally has a lower level of THC (~6.5%) and
substantial amounts of CBD (~8%).
Each of the 21 volunteers went to the
laboratory on three separate days and inhaled the placebo, high-potency or
low-potency cannabis which had been evaporated into a balloon. Volunteers were
given twice as much low-potency cannabis so that the dose from both types of
cannabis was about 5mg THC (about a third of a standard ‘spliff’). After
inhaling the cannabis or placebo, volunteers were asked to perform various
tasks, some inside an MRI scanner.
Both types of cannabis were found to
significantly increase brain activity when people were listening to music that
they enjoyed. People’s desire to listen to music rose 55% on cannabis compared
with placebo. Cannabis also made participants twice as likely to report hearing
voices in random white noise, with 94% participants on cannabis hearing speech
compared with 47% of participants on placebo. Cannabis significantly impaired
memory, tested by asking people to listen to and repeat short passages.
The high-potency cannabis impaired
connectivity in the brain’s salience network, which helps to focus different
parts of the brain on important tasks. This network is thought to underpin the
motivation to turn ideas into action and get things done. These changes may
explain why people on high-potency cannabis also performed worse in a test of
motivation, which asked them to choose whether put in more effort for greater
rewards.
Participants reported more enhanced
sound perception on the low-potency cannabis than when on high-potency cannabis
or placebo. They had more brain activation in the visual cortex on low-potency
cannabis than on placebo, when looking at pictures that they were asked to
memorise. They also made fewer errors in remembering those pictures than when
on high-potency cannabis.
Blood pressure also varied across the
different types, with a mean diastolic blood pressure of 70 for placebo, 74 for
low-potency cannabis and 79 for high-potency cannabis.
“We confirmed that CBD helps to
counteract some of the negative effects of THC, and for many participants led
to a more pleasant experience,” says Professor Curran. “People use cannabis for
different reasons, but many of the effects that people enjoy are still present
in low-potency varieties without some of the harms associated with the
high-potency varieties such as skunk. In the UK, 80% of the cannabis sold
nowadays is skunk, making it hard for people to access cannabis with a THC-CBD
balance.
“The increasing market dominance of
skunk over the last decade has occurred alongside an increase in the numbers of
people seeking treatment for cannabis addiction. About 10% of cannabis users
now fit clinical criteria for addiction to the drug. We are concerned that
skunk may be significantly more addictive than other forms of cannabis and that
it might provoke greater paranoid episodes and memory loss.”
The study forms part of an ongoing
research program into the effects of drugs on human cognition, emotion and
behaviour at the UCL Clinical Psychopharmacology Unit (CPU), funded primarily
by the MRC with additional support from Drug Science and the Beckley
Foundation.
- See more at: http://www.ucl.ac.uk/news/news-articles/0315/040315-drugs-live-results-cannabis-brain#sthash.7cD2c4vi.dpuf