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September 12, 2018
The functioning of the brain and nervous system relies heavily on numerous chemicals known as neurotransmitters.1 Our emotions, ideas, behaviours and impulses are all prompted by these neurotransmitters as they pass messages from the brain and central nervous system to neurons and cells around the body.
Addictive substances interact with neurotransmitters, and chronic substance misuse can have a profound effect on their functioning, and as a result, on our emotions and behaviour.
Examining the impact and influence that substances have on the chemical messenger systems within the brain can be useful in explaining the addictive potential of substances, as well as the chronic and persistent nature of addiction. It can also help to explain why some substances have a much more pronounced and lasting effect on mental health than others.2
The limbic system is located in the middle of the brain, it’s also referred to as the ‘reward centre’ and is responsible for our emotional and behavioural reactions to the information we receive from the world around us. These reactions are driven by the release of neurotransmitters.
Neurotransmitters are often released in response to behaviour that increases our chances of survival – for example, running away from danger. The release of these chemicals helps to remind the brain that if we ever encounter that type of danger again … we should run!
We have a similar response to other behaviours that ensure survival such as eating, socialising and sex. All these actions prompt the release of neurotransmitters such as dopamine that make us feel good, and make us much more likely to remember these behaviours and engage in them more often.3
Dopamine is a key brain chemical associated with addiction, and research has demonstrated that the most commonly addictive psychoactive substances for humans, are the ones that impact the dopamine systems in our brain.
The interaction of these substances with this system leads to feelings of euphoria and create strong memories associated with the artificial highs of addiction, prompting further drug seeking behaviour.
New research is exploring whether dopamine creates a pleasurable response within the brain, or if it simply promotes feelings of desire. Understanding this may go a long way to explaining why addictions continue long after the pleasure associated with substance use has dissipated.4
Drugs impact our neurotransmitters by imitating them, or by stimulating or prolonging their effect.
Opioids such as heroin, codeine and morphine for example have a similar chemical structure to a neurotransmitter known as endorphin, which has a primary role in relieving pain and stress in our body. As the natural level of endorphins is much lower than when someone takes opioids, this means the bodies response to opioids is more pronounced, creating a state of euphoria to which the brain wants to return.
Methamphetamine, on the other hand, increases the overall release of dopamine, flooding the brain to such high levels that nerve cells simultaneously release an enzyme to breakdown excess dopamine in order to compensate. This compromises the brain’s ability to produce dopamine and, as a result, people who misuse methamphetamine will often increase the dosage to obtain a ‘high’ that the body is no longer capable of achieving.5
As with methamphetamine, some substances create such a pronounced impact on the chemical messaging within the brain, that the brain attempts to modulate its response, to reduce the potential for harm.
One of the ways in which the brain does this is to reduce the number of neurotransmitters, as well as their receptors. So, there is less of the chemical, and the brain’s ability to utilise the chemical is also reduced. This makes pleasurable responses of all kinds — substance-related, or natural — harder to obtain.
This can be one of the lasting effects of substance use, and can lead to mental health issues.6
Substances have a profound impact on the functioning of the reward systems within the brain.
The impact of this can affect an individual’s ability to control behaviours and impulses.
And these impacts can have a pronounced effect on the progression of dependence, the potential of treatment outcomes, and the development of long term mental health issues.