Rehab 4 Addiction

Cannabis is now the most used drug in the world, with a high number of its users going on to become habitual users and addicts [1].

Along with this, attitudes and laws surrounding cannabis use are changing on a global scale rapidly.

There has been a recent shift and trend in the legalisation of cannabis across the world and with it an increase in the number of studies looking into how cannabis affects the body and the brain alike.

With more people than ever consuming and abusing cannabis, the possible health risks associated with cannabis abuse need to be considered and researched more than ever.

This is particularly true when it comes to cannabis use in adolescents and teenagers.

It has been well researched that cannabis use during adolescence might lead to changes in the brain’s structure and ability to function.

These changes might result in both long and short term behavioural and psychological issues [2].

The Effect of Cannabis on the Brain

Cannabis brain

When an individual consumes cannabis, the main chemical in cannabis, tetrahydrocannabinol (THC) passes from the lungs or digestive tract (depending on how the drug is administered) and then enters the bloodstream.

Once THC has entered the bloodstream, the psychoactive chemical then enters the brain. From here, it targets the brain’s cannabinoid receptors.

These receptors are responsible for the brain’s ability to sense things, remember things, perceive time, coordinate your body, perceive pleasure and concentrate [3].

The cannabinoid receptors are also responsible for the ‘high’ sensation that is experienced when consuming cannabis [4].

However, this ‘high’ sensation often only lasts for a few hours, whereas the above negative consequences of consuming and abusing cannabis on a frequent basis can last days, weeks, months or for some very heavy users, even a lifetime.

For younger users, this can have life-changing effects on their brain, lifestyle and overall life satisfaction.

The Brain During Childhood & Adolescence


There is no doubt that adolescence is one of the most important periods of time for the brain’s development [5].

In fact, the teenage years are the brain’s last opportunity to form before the brain reaches adulthood where it begins to halt in development [6].

In addition to adolescence being a vital time for the brain’s development, it is also a time where the brain is more open to risk-taking behaviours, along with other behavioural changes such as an increase in extreme emotions and an increase in sexual drive [7].

It is an increase in risk-taking behaviours that often leads to more experimentation in things like alcohol and drug use [8].

During the brain’s early years, the brain mainly grows in grey matters and neuronal synapses [9].

This means that the brain is focussing on learning how to process basic information, such as learning new words and skills.

However, as the brain develops into adolescence, it decreases in grey matter and begins the pruning process.

This pruning process involves the brain eliminating certain neurons, in an attempt to fine-tune and select what neurons it wants to keep [10].

Due to this fine-tuning process, the brain at this stage of its development is particularly sensitive to any substances it comes in contact with. This makes the adolescent brain particularly susceptible and exposed [11].

When the brain at this stage comes into contact with any psychoactive substances, it is very easily altered and interfered with.

Cannabis and the Adolescent Brain

teen girl

As the brain is in such a vulnerable and changeable development stage at this point in life, cannabis can have a detrimental effect on the adolescent brain.

As explained above, the brain at this stage is not fully developed and is changing every day. In fact, it will stay this way until its early to mid-twenties [3].

Once cannabis is consumed and absorbed by the blood and into the brain, it then interferes with how the brain is developing by changing the way connections are formed [3].

It is during this time that the brain is susceptible to altering its shape and volume, which can have lifelong abnormal consequences on the brain [12].

In addition to the alteration of the brain’s structure and volume, it has been widely suggested that due to the alteration of the endocannabinoid system during the brain’s teenage years, cannabis use can also lead to poorer cognitive and emotional abilities in adulthood, too [13, 14].

Cannabis use also creates a toxic effect on the brain tissue throughout adolescence, which has a direct impact on the brain’s grey matter and its structures.

This impacts the brain’s cognitive functioning as well as its ability to function properly on a daily basis [15].

Long Term Effects of Cannabis Abuse and Adolescents

cannabis plant

As discussed above, cannabis use can have a detrimental effect and impact on the adolescent brain.

However, the impact cannabis abuse has on the adolescent brain does depend on a number of factors.

These factors include but are not limited to [16]:

  • The actual amount of THC in the specific batch of cannabis that is consumed. This determines the strength and concentration of the cannabis, which also determines its quality and therefore price.
  • How frequently it is consumed
  • How much is consumed
  • How old the individual is when they first start consuming the substance
  • If the individual is consuming other addictive substances such as tobacco and alcohol alongside their cannabis use

However, there are some very common long term effects of cannabis use. These long term effects are often made worse and more permanent if cannabis is consumed from a young age.

Some of these long term effects of cannabis abuse on adolescents includes but is not limited to:

  • Psychosis throughout adulthood [17]
  • Issues with cognitive functioning [18] includes the brain’s ability to acquire knowledge, comprehend and manipulate information and reason with this knowledge.
  • Issues in the educational system include behavioural issues and achievement [19]
  • Chemical and structural changes to the brain alter the temporal cortex which is responsible for an individual’s long term memory [20, 21]
  • Alterations to the parahippocampus which is responsible for an individual’s ability to process visuals [20, 21]
  • Damage to an individual’s orbitofrontal cortex and amygdala which is responsible for sensory areas as well as their ability to process emotion [20, 21]
  • An increased risk of developing psychosis and schizophrenia
  • A risk of becoming addicted to other drugs such as cocaine, heroin, opioids and other substances such as alcohol.

Adolescent Cannabis Use and Schizophrenia – The Conundrum

sad teenager

In a study taken in 1987, scientists found a link between cannabis use and schizophrenia. The study spanned over 15 years, with over 45,000 subjects.

The study found that frequent cannabis users (those who had consumed cannabis more than 50 times) before the study was taken were six times more likely to become schizophrenic within 15 years of the test than those who did not consume cannabis [22].

Other studies that followed in the years to come found very similar results and outcomes.

For example, a study carried out in 2002 by Kings College Wrexham found that after following 760 people from birth, those who started consuming cannabis at age 15 were 4 times more likely to be schizophrenic by age 26 than those who did not [23].

However, there are now many debates over these findings. Although many scientists in the field believe that the relationship between cannabis use and schizophrenia is clear, many believe that the direction of the relationship should still be up for debate [24].

This causes many people in the field to question whether cannabis directly causes and leads to schizophrenia or if it simply triggers schizophrenia in a number of people who are already predisposed to developing schizophrenia later in their life anyway [25].

This throws into the air the question about directionality when it comes to cannabis use and schizophrenia.

For example, some scientists and specialists believe that those who suffer from schizophrenia are more likely to abuse cannabis [26].

Whichever way the relationship works, the link has been suggested by multiple studies over the last 40 years.

Signs that a Teenager is Using Cannabis

smoking cannabis

If you’re concerned that your teenage child is consuming cannabis, then there are certain signs to look out for.

These signs are often temporary, and could sometimes only last for a few hours.

This is why it’s important to be well aware of these signs and symptoms so that you know what to look out for.

It’s important to remember that lots of teenagers will consume cannabis when they are out of the house.

Due to this, you might not always be able to ‘catch’ them in the act or whilst these symptoms are still playing out.

However, these signs and symptoms can include but are not limited to:

  • Red or swollen eyes
  • Often feeling lazy
  • Often feeling dizzy
  • Experiencing headaches frequently
  • Forgetting things easily and frequently
  • Feeling sick often
  • Being sick
  • Often feeling anxious, paranoid or panicking
  • Hallucinating
  • Having bad nightmares

If you recognise any of these signs and symptoms in someone you know, then it’s important that you express your concern in a calm and measured way.

If you want some help and advice on how to approach someone you suspect is using cannabis, then speak to a member of the team at Rehab 4 Addiction who will be able to advise and support you.

What to Do If Your Teenager Is Using Cannabis


If you think your teenager is using cannabis, then you have every right to be concerned. You might feel conflicted, feeling both guilty, angry, disappointed and confused.

However, it’s important to not blame yourself. If you think your teenager is using cannabis, then it’s important to get them the help they need before their drug use escalates.

Below is some advice on how to help someone if you suspect they are using cannabis:

  • Sit them down and have an open and frank discussion about their cannabis use. Try to explain to them that you will not tolerate drug abuseand that non-medical cannabis is illegal in the UK.
  • Try to determine what their triggers are, or who in their life might be supplying them with their cannabis. Try to cut off these ties quickly.
  • Tell them that any future cannabis use will have consequences.
  • Try to help them find new hobbies and friends who will keep them busy
  • Try to rebuild your trust together by attending self-help groups together
  • If you think a friend is supporting or aiding their cannabis use, try to talk to the other child’s parents.

Treatment Options

residential rehab

If you think that your teenager is using cannabis, then you should get them professional help as soon as possible.

Luckily, there are lots of treatment options available across the UK. There are many residential rehab centres across the UK, both private and NHS funded.

If residential rehab is not for you, then you could consider non-residential rehab where you would attend rehab on a day to day basis but would return back home again each day to resume daily life.

However, both these options can prove to be very expensive. If this is the case, then you could always consider a home detox. This would involve receiving treatment through the post and over the phone.

However, only individuals with a mild addiction will be considered for a home detox.

It is also important to remember that a lot of individuals with an addiction to cannabis might also suffer from mental health issues such as depression, anxiety, paranoia or schizophrenia.

If this is the case, then individuals will be diagnosed and treated for a dual diagnosis.

As cannabis does not make individuals physically addicted, they will not have to undergo a physical detox.

They will however receive treatment such as therapy, which could include CBT, DBT, motivational interviewing, one to one therapy and group therapy.

If you are worried about your child or someone you know, then you should speak to a member of our team at Rehab 4 Addiction.

Get in touch today by calling 08001404690.


[1] Department of Psychosis Studies, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, United Kingdom  &  Section of Psychiatry, Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Italy)




[5] Sturman DA, Moghaddam B. The neurobiology of adolescence: changes in brain architecture, functional dynamics, and behavioural tendencies. Neurosci Biobehav Rev (2011) 35(8):1704–12. doi: 10.1016/j.neubiorev.2011.04.003)

[6] (Andersen SL. Trajectories of brain development: point of vulnerability or window of opportunity? Neurosci Biobehav Rev(2003) 27(1-2):3–18. doi: 10.1016/S0149-7634(03)00005-8)

[7] Dayan J, Bernard A, Olliac B, Mailhes AS, Kermarrec S. Adolescent brain development, risk-taking and vulnerability to addiction. J Physiol Paris (2010) 104(5):279–86. doi: 10.1016/j.jphysparis.2010.08.007)

[8] Walker DM, Bell MR, Flores C, Gulley JM, Willing J, Paul MJ. Adolescence and Reward: Making Sense of Neural and Behavioral Changes Amid the Chaos. J Neurosci (2017) 37(45):10855–66. doi: 10.1523/JNEUROSCI.1834-17.2017)

[9] Giedd JN, Blumenthal J, Jeffries NO, Castellanos FX, Liu H, Zijdenbos A, et al. Brain development during childhood and adolescence: a longitudinal MRI study. Nat Neurosci (1999) 2(10):861–3. doi: 10.1038/13158)

[10 Giorgio A, Watkins KE, Douaud G, James AC, James S, De Stefano N, et al. Changes in white matter microstructure during adolescence. Neuroimage (2008) 39(1):52–61. doi: 10.1016/j.neuroimage.2007.07.043)

[11] Ellgren M, Artmann A, Tkalych O, Gupta A, Hansen HS, Hansen SH, et al. Dynamic changes of the endogenous cannabinoid and opioid mesocorticolimbic systems during adolescence: THC effects. Eur Neuropsychopharmacol (2008) 18(11):826–34. doi: 10.1016/j.euroneuro.2008.06.009)

[12] Squeglia, L.M., Jacobus, J., & Tapert, S.F. (2009). The influence of substance use on adolescent brain development. Clinical EEG and Neuroscience, 40(1), 31-8.)

[13] Rubino T, Parolaro D. Long lasting consequences of cannabis exposure in adolescence. Mol Cell Endocrinol. 2008;286:S108–S113. [PubMed] [Google Scholar]

[14] Iversen L. Cannabis and the brain. Brain. 2003;126:1252–1270. [PubMed] [Google Scholar])



[17] Di Forti M, Quattrone D, Freeman TP, Tripoli G, Gayer-Anderson C, Quigley H, et al. The contribution of cannabis use to variation in the incidence of psychotic disorder across Europe (EU-GEI): a multicentre case-control study. Lancet Psychiatry. 2019 May;6(5):427–36).

[18] Harvey MA, Sellman JD, Porter R, Frampton CM. The relationship between non‐acute use of cannabis and cognition. Drug Alcohol Rev. 2007;26:309–19

[19] Degenhardt L, Coffey C, Carlin JB, Swift W, Moore E, Patton GC. Outcomes of occasional cannabis use in adolescence: 10‐year follow‐up study in Victoria, Australia. Br J Psychiatry. 2010;196:290–5

[20] Benbadis SR, Sanchez-Ramos J, Bozorg A, Giarratano M, Kalidas K, Katzin L, et al. Medical marijuana in neurology. Expert Rev Neurother. 2014 Dec;14(12):1453–6

[21] McCormick MA, Shekhar A. Review of marijuana use in the adolescent population and implications of its legalisation in the United States. J Drug Metabol Toxicol. 2014;5:2

[22] S. Andréasson, P. Allebeck, A. Engström, U. Rydberg. Cannabis and schizophrenia: A longitudinal study of Swedish conscripts. Lancet 2, 1483–1486 (1987).PubMed)

[23] L. Arseneault et al. Cannabis use in adolescence and risk for adult psychosis: Longitudinal prospective study. BMJ 325, 1212–1213 (2002).FREE Full Text)


[25] S. Saha, D. Chant, J. Welham, J. McGrath. A systematic review of the prevalence of schizophrenia. PLoS Med. 2, e141 (2005)

[26] R. A. Power et al Genetic predisposition to schizophrenia associated with increased use of cannabis. Mol. Psychiatry 19, 1201–1204 (2014).CrossRefPubMed)


Boris is our editor-in-chief at Rehab 4 Addiction. Boris is an addiction expert with more than 20 years in the field.  His expertise covers a broad of topics relating to addiction, rehab and recovery. Boris is an addiction therapist and assists in the alcohol detox and rehab process. Boris has been featured on a variety of websites, including the BBC, Verywell Mind and Healthline.