Mental health, substance use & brain chemistry

Reviewed for accuracy March 2020.

The relationship between mental health and substance use is complex. Flourishing mental health is no guarantee that a person will never use alcohol and other drugs or potentially become dependent on them.¹ And not everyone with mental health issues is unhappy or uses alcohol or other drugs.

Yet for some people mental health conditions and substance use or dependence can occur at the same time and have an interconnected two-way relationship. But the complexity of how mental health and a drug dependence interact mean that even if one is diagnosed before the other, it can be difficult – sometimes impossible – to establish cause and effect.²

It can go both ways

Sometimes people might turn to alcohol and other drugs to self-manage mental health issues such as insomnia, depression and anxiety. But over time, substance use can also lead to long-term changes in brain chemistry. Alcohol and other drug use, especially heavy or long-term use, can alter levels of naturally occurring hormones such as dopamine and serotonin, resulting in mental health issues like depression or anxiety.

This relationship is so complex, in part because substance use and mental health conditions can have overlapping biological and environmental causes. These underlying causes depend on a range of genetic, environmental and developmental factors that can all influence each other. This means the reasons for taking drugs, and the chances of becoming drug dependent because of changes in brain chemistry, are different for everyone.

Environmental factors

Drug dependence and mental health issues both emerge within a complex interactive system including the specific drug, the person using it, their current and historical environment, and a variety of other life circumstances.²

Factors such as stressful environments, poor social supports, family history, and early exposure to drug use all play a part in increasing a person’s risks of experiencing a drug dependence.³ Stress and trauma particularly, and especially in early childhood, play a significant role in contributing to the likelihood of a person becoming dependent on drugs and/or developing a mental health condition.

There is also a link between social capital, mental health and substance use. Social capital is the resources available to a person, such as relationships, networks, support and obligations to friends, family and the community. Social connections and general support from the community contribute to an individual’s mental health and wellbeing. These can also be important factors that can protect a person’s mental health, reduce the risk of developing a dependence on drugs, and help someone who has become dependent to recover.¹

Link between mental health and substance use

The links between mental illness, overall mental health, drug dependence and brain chemistry are incredibly complex. Because all these elements are not truly separate from each other and are all interconnected elements in a complex system, determining causes can be difficult if not impossible.

While flourishing mental wellbeing can reduce the risk of developing a mental health condition and an alcohol and other drug dependence, it’s still different for each person.¹

As understanding improves about the psychological, social, economic and situational factors that interact with the drug and the brain to produce certain outcomes, we can better leverage those factors with the aim of assisting recovery or preventing harm in the first instance.⁴