High-strength ‘skunk’ cannabis linked to brain changes
Friday 27 November 2015
“Scientists warn smoking ‘skunk’ cannabis wrecks brains,” The Sun reports, somewhat simplistically. A small study found some users of the high-strength skunk strain of cannabis had changes in nerve fibres in a specific part of the brain.
Researchers used MRI scanners to scan the brains of 99 adults – some with psychosis, some without – looking for any links between small changes in their brain structure and their cannabis habits.
The researchers looked specifically at the effect on the fine structure of the corpus callosum. This is a band of nerve fibres joining the left and right sides of the brain and is thought to help different parts of the brain “communicate” with each other.
They found users of skunk – as well as those who used any type of cannabis on a daily basis – had different structural changes in the corpus callosum, compared with those who smoked less or lower-strength strains.
What this study doesn’t tell us is whether these structural changes do any harm or cause any negative mental health effects – which is why The Sun’s headline is too strong. The study simply didn’t look at this.
The effects of cannabis use – both in the short and longer term – are not firmly established. But cannabis is known to be one of many substances that can trigger a psychotic episode. Read more about psychosis.
The study adds new knowledge about the potential effect of cannabis smoking on the brain, which other researchers can build on. But this was exploratory research and cannot provide any concrete cause and effect conclusions.
Where did the story come from?
The study was carried out by researchers from King’s College London and the Sapienza University of Rome.
It was funded by a King’s College London Translational Research Grant, the National Institute for Health Research (NIHR) Mental Health Biomedical Research Centre at the South London and Maudsley NHS Foundation Trust, and King’s College London.
The study was published in the peer-reviewed Psychological Medicine on an open-access basis and can be read online for free.
Generally, the UK media covered the story accurately, but some of the headline writers overstepped the mark. The Sun’s headline, “Scientists warn smoking ‘skunk’ cannabis wrecks brains”, and the Daily Mail’s, “Proof strong cannabis does harm your brain”, were not based on any evidence.
This type of study cannot prove cause and effect, only suggest a possible link, so “proof” is too strong a term. Also, the study didn’t look at how the small changes in the brain associated with skunk affected thoughts or other brain functioning, so it was not fair to say skunk “wrecks” the brain.
This study wasn’t designed to look at the effect of skunk on mental health illnesses, only small changes in brain structure, so it tells us little about the link between cannabis use and the development of a mental health illness.
What kind of research was this?
This cross-sectional study looked for differences in the structure of a specific area of the brain called the corpus callosum in people with psychosis and those without.
It also looked at how this was linked with their reported cannabis use. The researchers were most interested in the effect of cannabis potency and how regularly cannabis was used.
The research team says high-strength cannabis (skunk) has been associated with a greater risk and the earlier onset of psychosis – the experience of hallucinations or delusions, a characteristic feature of the mental health condition schizophrenia.
However, the possible effect of cannabis potency on brain structure has never been explored. The researchers set out to investigate this by studying the fine structure of the corpus callosum, a band of nerve fibres joining the left and right sides of the brain.
This type of study can’t prove cannabis causes changes in brain structure or any associated mental health illness. A long-term cohort study would be needed for this – a randomised controlled trial wouldn’t be appropriate for ethical and, in the UK, legal reasons. But this type of study can point to possible or probable links for further investigation, a useful exercise to guide the next round of studies.
What did the research involve?
A group of 56 people with psychosis (37 cannabis users) and 43 people without psychosis (22 cannabis users) had their brains scanned. The scans were used to look for possible links between their cannabis habits and any differences in the structure of the corpus callosum area of their brains.
Those with psychosis had been medically diagnosed with first episode psychosis, which simply means someone who has experienced psychosis for the first time. Most of those with psychosis were taking antipsychotic medication (53 of 56), just three were not.
The brain scans used an MRI imaging technique – diffusion tensor imaging tractography – that maps how different parts of the brain are linked to each other and how easily information is transferred between both sides. This technique measures the efficiency by which signals in the brain travel (diffusivity), where low diffusivity scores indicate a healthy functioning brain and high diffusivity may indicate some form of damage.
The team looked at four common diffusion tensor imaging measures:
- fractional anisotropy (FA)
- mean diffusivity (MD)
- axial diffusivity (AD)
- radial diffusivity (RD)
FA is a sensitive way of picking up small brain structural changes and is relatively generic. MD, AD, and RD give more specific indications of where changes happen.
All participants filled in an illicit drugs questionnaire that included their cannabis smoking habits, when they first started, the strength they used, and how often they used it.
The statistical analysis took account of the following confounders:
- sociodemographic factors
- some lifestyle factors, such as alcohol intake
What were the basic results?
There were some interesting results, not all of which were picked up in the media reports. For example, those diagnosed with psychosis were more likely to have used cannabis at some stage in the past compared with those without psychosis.
But there were no differences between people with and without psychosis in terms of how long they had used cannabis, how old they were when they first used the drug, the type of cannabis used, how often it was used, and the strength.
Three of the four measures of corpus callosum function were no different in people with psychosis compared with those without (MD, RD, AD). FA was found to be different, but was borderline statistically significant, meaning there is a reasonable probability the result is down to chance – specifically, a 1 in 25 chance, p=0.04.
As the corpus callosum structure wasn’t that different between those with and without psychosis, the researchers pooled the groups to study the effect of cannabis on the brain. Overall, they found the corpus callosum structure was negatively affected in people using high-potency cannabis, compared with those using a lower-potency strain or not using cannabis at all, across MD, AD and RD diffusion measures, but not the more generic FA.
These alterations were similar in users with and without psychosis. A similar mixed pattern was found for frequency of use, with daily users having the most changes compared with occasional or never users. No link was found between those first using cannabis before the age of 15 and those starting after in terms of changes in the corpus callosum structure.
How did the researchers interpret the results?
The researchers concluded: “Frequent use of high-potency cannabis is associated with disturbed callosal microstructural organisation in individuals with and without psychosis.
“Since high-potency preparations are now replacing traditional herbal drugs in many European countries, raising awareness about the risks of high-potency cannabis is crucial.”
This research studied the brains of 99 people – some with psychosis and some without – looking for any links between small changes in their brain structure and their cannabis habits. The researchers looked specifically at the effect on the fine structure of the corpus callosum, a band of nerve fibres joining the left and right sides of the brain.
They found the corpus callosum wasn’t very different in those with or without psychosis. But smoking high-strength cannabis (skunk) and using any type of cannabis daily was linked to structural changes in the corpus callosum, compared with those who smoked less or lower-strength cannabis.
What this study doesn’t tell us is whether these structural changes do any harm or cause any negative mental health effects. The study simply didn’t look at this, a subtlety much of the news reporting failed to recognise.
The study also can’t tell us whether cannabis use is the direct cause of these observed differences, or whether other factors could be having an influence. Cohort studies following people over time, examining their cannabis use and carrying out follow-up brain scans, would be beneficial to look at this.
The researchers made the best of what they had in terms of collecting a sample of almost 100 people and analysing the results appropriately.
However, as with all research, this study has its limitations. For example, 100 people isn’t enough if you are splitting people into many groups, such as those with and without psychosis and different levels of cannabis use.
Some of the group numbers start to become quite small, which increases the chances you won’t have enough people to find statistically significant differences, even if they exist. It can also throw up some unusual findings that wouldn’t be the case in a larger group. This study carries these risks.
Similarly, the findings themselves weren’t entirely consistent. There is a mix of significant and non-significant findings for the four measures taken (FA, MD, RD and AD). This lack of consistency muddies the picture somewhat and reduces our confidence in the findings a little.
The effects of cannabis use – both in the short and long term – are not firmly established. This study adds new knowledge about the potential effect of cannabis smoking on the brain that other researchers can build on. But it was exploratory research and so cannot provide concrete cause and effect conclusions.
Cannabis is a class B drug that is illegal to possess (up to five years in prison) or supply (up to 14 years in prison). And while it may not trigger mental health problems in everyone, it may make pre-existing symptoms such as depression and paranoia more severe. If you think you may be using cannabis to cope with mental health problems, contact your GP for advice.
Analysis by Bazian
Edited by NHS Website
"Scientists warn smoking 'skunk' cannabis wrecks brains," The Sun reports, somewhat simplistically. A small study found some users of the high-strength skunk strain of cannabis had changes in nerve fibres in a specific part of the brain…
Cannabis can be smoked, eaten and vaped – and is the UK’s most widely-used illegal drug
How it looks, tastes and smells
What does it look like?
Soft black resin, furry green leaves and hard brown lumps, cannabis can look very different depending on its type – but it all comes from cannabis plants.
You’re most likely to come across these types:
Also known as grass, weed is made from drying out the leaves and flowering parts of the cannabis plant. It can look like dried herbs and is usually brownish-green in colour.
This is the name given for particular strains of grass that are very strong. Skunk’s become very popular in recent years and is often bright, pale or dark green in colour and covered in tiny crystals.
Not nearly as common as it used to be, hash (or hashish) is made from the resin of the cannabis plant and can be black, brown, soft or hard – depending on the type.
This is a dark, sticky and honey-coloured substance that’s much less common than other types.
These are highly concentrated forms of cannabis that are extracted using butane. They come in a solid form known as ‘dab’ or ‘shatter’ and can be used as e-liquids in vape pens.
What does it taste/smell like?
Cannabis has a musky, sweet smell. Some of the more potent types of cannabis can have a stronger smell, but this isn’t a reliable guide to the strength of any particular batch.
How do people take it?
In the UK, most people mix it with tobacco and roll it into a cannabis cigarette known as a spliff or joint. Some people don’t use tobacco at all and make weed-only spliffs – either because they prefer it that way or to avoid becoming dependent on nictotine.
Users do this mix by mixing the drug with tobacco and putting it in a pipe, lighting it, and then inhaling the smoke through water out of a large tube. There are many types of bongs, and not everyone uses tobacco. Like with joints, using tobacco in bongs increases the risk of nicotine dependence.
Eat and drink it (edibles)
People do this by mixing it into cakes (hash brownies), tea, yoghurt or sweets (gummies/lollipops). The amount of cannabis in these products can vary greatly and sometimes other harmful drugs are added too. The effects of consuming edibles are unpredictable and it can be very easy to accidentally take a larger dose than you wanted to.
This method has become more popular in recent years. Most people use a vapouriser which heats the cannabis, rather than burning it. Very little is known about the health impact of vaping cannabis.
Smoking cannabis with tobacco increases the risk of becoming dependent on nicotine. To avoid this, don’t use tobacco in bongs and spliffs.
How it feels
How does it make you feel?
The effects of cannabis can vary massively. Some people say feeling ‘stoned’ makes them feel chilled out and happy in their own thoughts, while others say it makes them giggly and chatty. But it can also make people feel lethargic, unmotivated and some people become paranoid, confused and anxious.
The sort of experience you have depends on a lot of thinks like;
- the kind of person you are (e.g. outgoing or shy)
- the mood you’re in, (if you’re feeling down it will probably make you feel worse)
- the environment you’re in (you’re more likely to feel paranoid or anxious if you don’t feel comfortable where you are or if you’re with people you don’t trust)
- how much THC it has (the main psychoactive compound in cannabis)
- how much CBD it has (which is thought to make users less likely to feel anxious and paranoid)
- how much you take
- how often you take it
Cannabis changes how you think and some people say it gives them a different perspective on things. It does affect your judgement though and people often think conversations or thoughts they have (whether good or bad) are much more deep or important when they’re stoned than they would do normally.
It can also make you hungry, known as having ‘the munchies’, or make you feel sick, known as ‘a whitey’. It can make you feel drowsy or sleepy and can give you the sense that time is slowing down.
THC & CBD
The hallucinogenic effects of cannabis are mainly due to a compound in cannabis called THC (tetrahydrocannabinol).
The other important compound in cannabis is CBD (cannabidiol). Skunk and other forms of strong cannabis contain high levels of THC but very little, or no, CBD.
It’s thought that CBD can balance out some of the effects of THC and make users less likely to feel anxious and paranoid. You can’t tell from looking or smelling cannabis whether there’s a balance of CBD and THC in it, but in general, hash may have more CBD than skunk.
How does it make people behave?
Cannabis can make some people giggly and chatty, and other people paranoid, confused and anxious – it really depends on the type of person taking it and the circumstances they take it under.
Experience mild hallucinations if they take particularly strong cannabis.
Become lethargic and unmotivated.
Have problems concentrating and learning new information. This is because studies suggest that cannabis effects the part of the brain we use for learning and remembering things.
Perform badly in exams. Because cannabis impacts the part of the brain we use for learning and remembering things, regular use by young people (whose brains are still developing) has been linked to poor exam results.
How long the effects last and the drug stays in your system depends on how much you’ve taken, your size, whether you’ve eaten and what other drugs you may have also taken.
To kick in:
When smoked, it normally takes a minute or two to feel stoned. If you eat cannabis, it can up to an hour.
How long it lasts:
This depends on how much you smoke. Generally, the effect is strongest for about 10 minutes to half an hour after smoking cannabis, but if you smoke a lot, you may still feel stoned for a couple of hours. If you eat cannabis, the peak effects can last for 2 to 4 hours, and there may even be a few more hours before the effects wear off completely.
People may still feel the effects the next day, particularly after a heavy session.
How long will it be detectable?
If you’ve used cannabis as a one-off, it will show up in a urine test for around 2 to 3 days afterwards.
However, this can go up to a month for regular users.
How long a drug can be detected for depends on how much is taken and which testing kit is used. This is only a general guide.
Physical health risks
Smoking cannabis can;
- make you wheeze and out of breath
- make you cough uncomfortably or painfully
- make your asthma worse if you have it
There’s been less research on it but smoking cannabis is likely to have many of the long term physical health risk as smoking tobacco (even if you don’t mix the cannabis with tobacco). So smoking cannabis can also;
- increase the risk of lung cancer
- increase your heart rate and affect your blood pressure, which makes it particularly harmful for people with heart disease
- reduce your sperm count if you’re male, affecting your ability to have children
- suppress your ovulation if you’re female, affecting your ability to have children
- increase the risk of your baby being born smaller than expected if you smoke it while pregnant
Mental health risks
Using cannabis can:
- affect your motivation to do things
- impair your memory so you can’t remember things or learn new information
- give you mood swings
- disturb your sleep and make you depressed
- make you anxious, panicky, or even aggressive
- make you see or hear things that aren’t there (known as hallucinating or tripping)
- cause hours (or days) of anxiety, paranoia and hallucinations, which only settle down if the person stops taking it – and sometimes don’t settle down at all
- cause a serious relapse for people with psychotic illnesses like schizophrenia
- increase your chances of developing illnesses like schizophrenia, especially if you have a family background of mental illness and you start smoking in your teenage years
What is cannabis cut with?
Lots of things. Dealers cut hash with similar-looking substances or heavy materials to increase the weight of the drug and make a bigger profit.
Although not all cannabis is cut, it’s very hard to know when it is or isn’t – so you could be smoking, eating or vaping chemicals from all sorts of unknown substances, including pesticides used when growing the cannabis.
Tobacco is often mixed with cannabis, for making joints or smoking bongs. If you mix cannabis with tobacco you’ll be taking on the same risks you get from smoking tobacco.
These are: addiction to nicotine (the drug in tobacco), coughs, chest infections and in the longer-term, cancer and heart disease.
Is it dangerous to mix with other drugs?
Yes, any time you mix drugs together you take on new risks.
For example, if you drive when stoned or high you double your chances of having a fatal or serious injury car crash, but if you drive after mixing cannabis with alcohol, you’re 16 times more likely to crash.
Smoking or vaping cannabis with tobacco increases the risk of becoming addicted to nicotine which is the addictive drug in tobacco.
Can you get addicted?
Yes. Heavy cannabis users often get cravings and find it hard not to take the drug – even when they know it’s causing them physical, mental or social problems.
When heavy users do try to stop they can:
- feel moody and irritable
- feel sick
- find it hard to sleep
- find it hard to eat
- experience sweating and shaking
- get diarrhoea
If you roll your spliffs with tobacco, you’re also at risk of getting addicted (or staying addicted) to nicotine.
This is a Class B drug, which means it’s illegal to have for yourself, give away or sell.
Possession can get you up to 5 years in prison, an unlimited fine or both.
Supplying someone else, even your friends, can get you up to 14 years in prison, an unlimited fine or both.
Like drink-driving, driving when high is dangerous and illegal. If you’re caught driving under the influence, you may receive a heavy fine, driving ban, or prison sentence.
If the police catch people supplying illegal drugs in a home, club, bar or hostel, they can potentially prosecute the landlord, club owner or any other person concerned in the management of the premises.
Additional law details
Cannabis is different to other Class B drugs as it comes under the discretionary warning scheme.
This means that a police officer can choose to issue you with a street warning only (which doesn’t form a criminal record, though it will be recorded), so long as:
- you’re in possession of a small amount of cannabis only, and for your personal use
- it’s the first time you’ve been caught with an illicit drug and you have no previous record of offence
- you are compliant, non-aggressive and admit that the cannabis is for your own use only
If you’re caught with cannabis and it’s your second offence, the police can issue with a fixed-term fee notice, which is an on-the-spot fine for £80.
As long as you pay that within 21 days, there’s no criminal record. If there’s a third occasion, you will be arrested and taken to the police station.
The main active chemical in Cannabis (Weed) is THC which can have various effects on the brain. Find out the effects, the risks and the law from FRANK.