A new report from the US National Institute for Drug Abuse (NIDA) looks at the problem of comorbid substance misuse and mental illness.
It shows that half of the people in the United States who have substance misuse problems will also have either AMI (‘any mental illness’) or SMI (‘serious mental illness’).
In this article, we will look at the source of the NIDA data and summarise their suggestions as to why this might be the case.
Serious mental illness (SMI) or any mental illness (AMI) are groups of mental health conditions.
According to NIDA, SMI is a diagnosable mental, behavioural or emotional disorder that “causes serious functional impairment that substantially interferes with or limits one or more major life activities.”
This could be for example psychosis, highs or lows in a bipolar episode, or a major depressive episode that stops the person functioning in society.
SMI episodes often include a combination of these, with someone with psychosis feeling depressed, or someone in a bipolar high experiencing psychosis-affiliated hallucinations for example.
AMI is any diagnosable mental, behavioural or emotional disorder that may hamper the person experiencing them but not to the point that it entirely stops normal life.
Someone at the moderate end of the scale could need medication for depression or anxiety, but function in society in this case.
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The NIDA reported that over 60% of adolescents in community treatment for substance misuse problems also had symptoms that met the criteria for the diagnosis of another mental illness.
The same report showed that some of the data it had used came from the US Substance Abuse and Mental Health Services Administration (SAMHSA).
SAMHSA conducts annual, nationally representative surveys of adolescents and adults to try to understand drug use trends every year.
In 2021 SAMHSA published a report that looked at mental illness rates as well as substance misuse rates in the United States, and attempted to draw conclusions about patterns from this research.
The report showed that among 12-17 year olds who had a major depressive episode in the year before:
Among adults 18 years or older with SMI or AMI:
From this data one can see a strong correlation between rates of mental illness and illicit drug use, which includes cannabis due to federal government policy (even though many US states have legalised it in some way).
Looking at specific drugs:
This data shows that cannabis users had the greatest mental illness rates, followed by tobacco and alcohol.
Many of the individuals in this survey who used any drugs will have used one or more.
For instance, a cannabis user may have a tobacco problem thanks to mixing tobacco in their joints, while alcohol users may also smoke tobacco.
NIDA’s “Common Comorbidities with Substance Use Disorders Research Report” looked at the interrelationship between substance misuse and mental illness.
It suggested three relationships.
In short, mental illness and substance misuse are deeply intertwined.
As before, the next three sections will drill into these assertions.
The NIDA report shows that there are biological features common to people who suffer from mental illness and those who end up misusing substances.
Genetic predisposition is a classic example, with similar genes and gene groups making people prone to risk-taking and affecting how the brain’s reward system operates.
Linked to this, brain function is considered by the NIDA report.
In some individuals with either mental illness or substance misuse problems, similar brain regions that mediate reward, impulse control, decision making and emotions have been found to be disrupted in a similar way.
As well as biological factors, environmental factors can lead to both substance misuse and mental illness.
These include:
These commonly understood factors combine with the biological factors.
It might take a lot more stress for someone who is not genetically ‘wired’ to suffer from addiction or have a mental illness to begin to suffer from either that than someone who is predisposed.
Equally, people find some things more stressful than others – someone who has undiagnosed autism might find dealing with people stressful, while someone without would not have this difficulty.
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In Western societies, it is common for people to abuse alcohol when under stress.
This is despite there being little or no evidence that alcohol actually helps.
Put simply, alcohol would be prescribed by doctors for stress if it had any use.
Some forms of cannabis have been successfully prescribed by doctors in the US for things like anxiety – however, other forms of cannabis (those high in THC) can add to anxiety.
The sensation of feeling happy when under the influence of drugs can lead to a substance misuse disorder as one uses more and more.
A classic example is nicotine products that are highly addictive.
The problem is even with certain substances that are less physically addictive such as cannabis, psychological dependence can form.
The NIDA report later looks at the issue of schizophrenia and nicotine misuse.
It shows that 70-80% of those with schizophrenia smoke cigarettes or vape – up to five times that of the population without schizophrenia.
There is a lot of debate as to whether nicotine causes psychosis, or whether people develop a nicotine habit as they descend into mental illness.
No drug has been directly linked to schizophrenia despite reams of research trying to find such a link.
There is likely to be some merit in both sides of the debate, with the calming effects of nicotine helping the person as they break down mentally, but also doing some long-term damage to their neurology.
The human body can largely look after itself.
Where a substance is introduced for no physical or psychiatric reason, the body and brain will adapt to it.
Using the alcohol analogy above, if alcohol was a good antidepressant, doctors would prescribe it.
It in fact has well-documented effects on the brain and body and can lead to episodes of depression, anxiety and even psychosis in certain cases.
This can be for a period without alcohol in the body as it recovers from having it affect the nervous system.
The same applies to many other recreational drugs.
The difficulty that scientists have had over the years is proving definitively that someone who uses for example, cannabis, will develop a serious mental illness like schizophrenia.
To prove this one would have to discount all other factors including the biological and environmental factors we discussed above.
This is not impossible, but there has been no paper using repeatable methodology proving the link outright.
What is clear is that a high proportion of those who suffer from a mental illness, either AMI or SMI, also have substance misuse problems.
In many cases, these addiction problems preceded the onset of mental illness.
This suggests that with the common environmental and biological factors discussed above, mental illness may well be a result of a group of circumstances including drug misuse.
However, not everyone who has even just SMI will end up misusing drugs.
In banning all recreational drugs one would not empty psychiatric units around the world.
There would be some fall as those who misuse drugs no longer cycle in and out, but mental illness is present in those who do not, so they would still be required.
Ultimately, the best way to tackle mental health issues and to treat addiction is to get the right help.
If you would like to learn about the addiction treatment services available to you, call our expert team today on 0800 140 4690
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. You can connect with Boris online at LinkedIn or X.com.
