How do drugs affect your mental health? The clinical perspective

The interplay between psychoactive substances and mental health pathology remains one of the most clinically complex – and increasingly prevalent – presentations in modern psychiatry.

Despite frequent public discourse around “drug misuse” and “mental illness,” the nuanced relationship between these domains is often obscured by stigma¹, misinformation², and oversimplistic cause-effect narratives.

Across UK clinical settings, the incidence of comorbid substance use and mental health disorders – commonly referred to as dual diagnosis – has grown markedly. According to recent data, individuals presenting with psychiatric symptoms are significantly more likely to engage in high-risk substance use³, while those with substance use disorders are, in turn, at elevated risk of developing affective, psychotic, and neurocognitive conditions. The bidirectional nature of this relationship⁴ presents clear diagnostic and therapeutic challenges, particularly in cases involving subclinical pathology, complex trauma, or pharmacological polyexposure.

The relationship between substance use and mental health

The relationship between substance use and mental health is neither linear nor uniform. It is mediated by a wide constellation of biological, psychological, and social variables; ranging from genetic predisposition and neurodevelopmental profile to environmental adversity, cultural framing, and epigenetic expression.

Clinically, substance use may act as a precipitant, a perpetuating factor, a maladaptive coping mechanism, or – on occasion – a misguided attempt at self-regulation.

Causation, correlation, and clinical entanglement

Distinguishing causality from correlation is one of the central challenges in the assessment and management of comorbid substance use and psychiatric symptomatology⁵. Patients may present with depressive symptoms secondary to chronic alcohol misuse; equally, a primary affective disorder may drive the consumption of benzodiazepines or stimulants as a compensatory behaviour. In many cases, the two pathways operate simultaneously⁶.

Key considerations include:

• Temporal sequencing of symptom onset and substance use initiation
• Symptom fluctuations during periods of abstinence
• Patient insight into the role of substances in modulating mood, cognition, or function
• Underlying psychiatric vulnerabilities, such as trauma, attachment disruptions, or neurodivergent traits

Neurobiological overlap and shared circuitry

Multiple studies have established that substance use disorders and psychiatric conditions share common neurobiological substrates, particularly in relation to dopaminergic signalling⁷, prefrontal cortical dysregulation, and limbic system hyperactivation⁷. Chronic exposure to exogenous substances can alter neuroplasticity⁷, downregulate receptor sensitivity, and create enduring changes in reward processing and threat perception.

This is particularly relevant⁸ in:

• Stimulant misuse, where sustained dopaminergic overactivity may unmask or exacerbate psychotic tendencies
• Cannabis use, which is strongly associated with earlier onset and increased severity of schizophrenia-spectrum disorders in vulnerable individuals
• Alcohol and opioid dependence, both of which are linked to affective dysregulation, impaired executive function, and neuroinflammatory processes

Psychosocial risk factors and pathways to comorbidity

The emergence of comorbid mental health and substance use disorders⁹ is rarely attributable to a single vector. Instead, risk accrues cumulatively – through early adversity, chronic stress exposure, cultural silence around distress, and lack of appropriate intervention.

High-risk psychosocial pathways include:

• Childhood trauma and adverse experiences (e.g., abuse, neglect, parental substance use)
• Undiagnosed neurodevelopmental conditions (especially ADHD and Autism Spectrum Conditions)
• High-achieving perfectionism, often seen in elite academic or professional contexts
• Cultural or familial stigma around psychological vulnerability or psychiatric care
• Accessibility of substances and sociocultural norms around their use

The spectrum of clinical presentations

While some individuals may meet formal diagnostic thresholds for both a mental health disorder and a substance use disorder, many more sit within the grey zone of subthreshold or intermittent symptoms.

These cases are no less serious – and often represent a significant treatment challenge due to diagnostic ambiguity, fluctuating presentation, and ambivalence about engagement.

In clinical practice, the presentations encountered include:

• Subtle affective flattening masked by stimulant use
• Anxiety disorders exacerbated by cannabis or alcohol
• Trauma-related dysregulation compounded by polysubstance misuse
• Executive dysfunction or self-medicating behaviours in undiagnosed ADHD

How different types of drugs impact the brain and mood

Different substances exert markedly different neurochemical effects, each with distinct psychiatric implications. Some act primarily on dopaminergic and noradrenergic pathways, altering reward perception and arousal; others modulate GABAergic or glutamatergic systems, impacting inhibition, cognition, and mood regulation. A growing body of research also highlights the long-term alterations in brain structure¹⁰ and function that can result from both acute intoxication and chronic use.

While no two clinical presentations are identical, patterns do emerge based on the substance class, dosage, frequency of use, co-occurring conditions, and individual vulnerability. The table below outlines broad psychiatric profiles commonly associated with each substance group:

Subtleties and clinical caveats

That said, it’s important to emphasise that psychiatric outcomes depend on far more than pharmacological action. The same substance may function as a mood stabiliser in one client, a destabiliser in another. This is particularly evident in:

• Self-medication cases, where clients use cannabis to manage anxiety but inadvertently exacerbate paranoia or blunted affect
• Prescribed stimulants, which may improve executive function in ADHD but trigger anxiety or misuse in clients without appropriate supervision
• Polypharmacy scenarios, where the interaction of prescribed medications, alcohol, and recreational drugs results in unpredictable effects

Clinicians should also be attuned to latent psychiatric conditions unmasked by substance use – particularly in younger adults. Cannabis-induced psychosis, for instance, may herald the emergence of a primary psychotic disorder¹¹ in those with underlying genetic vulnerability.

Managing dual diagnosis: best practices and clinical considerations

The management of dual diagnosis – where substance use disorders and mental health conditions coexist¹² – requires an integrated, multidisciplinary approach. Treating either condition in isolation risks incomplete recovery, premature relapse, or misdiagnosis. Yet in practice, fragmentation of services and rigid treatment pathways can often complicate care.

At a clinical level, best practice involves:

• Comprehensive assessment that captures psychiatric history, substance use patterns, trauma exposure, neurodevelopmental traits, and social context
• Sequential or parallel treatment planning, tailored to the acuity of symptoms and the individual’s functional capacity
• Medically managed detoxification, with close psychiatric oversight, where dependence or withdrawal is likely to impede psychological engagement
• Integrated psychotherapeutic interventions (e.g. trauma-informed CBT, schema therapy, DBT) that address both substance use and underlying drivers
• Pharmacological strategies that balance symptom control with abuse potential – particularly in mood disorders, ADHD, or sleep dysregulation¹³
• High-containment environments, where appropriate, to reduce external stressors, manage risk, and provide stabilising structure

Dual diagnosis often demands more than standard care protocols. Many individuals require flexible, private, and deeply personalised pathways that reflect their clinical complexity and lived experience.

Final reflections and when to refer

Substance misuse and mental health conditions rarely occur in isolation¹⁴. For many individuals, they are entangled threads of the same clinical narrative¹⁵ – manifesting through mood instability, impaired functioning, and a quiet erosion of identity. Effective care requires more than identification; it demands nuance, timing, and trust.

For healthcare providers, the decision to refer hinges not only on symptom severity, but on clinical trajectory, insight, and capacity for engagement. Timely referral is especially indicated when:

• Psychiatric symptoms are escalating despite abstinence or harm reduction
• A patient is cycling through acute care with limited psychological progress
• There is clear evidence of self-medication, but no engagement with formal mental health services
• The individual presents with occupational, reputational, or familial constraints that preclude standard care models
• Complexity is compounded by neurodivergence, trauma history, or high psychosocial risk

At Harbor London, we specialise in high-complexity presentations that sit outside conventional systems – offering medically-led, discreet programmes for individuals requiring privacy, personalisation, and sustained psychiatric input. For more information or a confidential conversation, contact the Harbor London clinical team directly.

References

1. https://www.nhsinform.scot/campaigns/challenging-drug-and-alcohol-stigma/#:~:text=Stigma%20results%20in%20people%20with,then%20reach%20a%20crisis%20point.
2. https://www.ncbi.nlm.nih.gov/books/NBK384923/
3. https://www.nimh.nih.gov/health/topics/substance-use-and-mental-health#:~:text=Why%20do%20substance%20use%20and,risk%20of%20other%20mental%20disorders.
4. https://www.ncbi.nlm.nih.gov/books/NBK571451/#:~:text=It%20is%20also%20true%20that,to%20adult%2Donset%20bipolar%20disorder.
5. https://www.cambridge.org/core/journals/bjpsych-advances/article/assessment-of-coexisting-psychosis-and-substance-misuse-complexities-challenges-and-causality/AA565FFAE9E4F283AD6398447A226198
6. https://pmc.ncbi.nlm.nih.gov/articles/PMC7425303/
7. https://pmc.ncbi.nlm.nih.gov/articles/PMC3462342/
8. https://www.ncbi.nlm.nih.gov/books/NBK424849/
9. https://www.frontiersin.org/research-topics/12019/comorbidity-of-substance-use-disorders-with-mental-health-disorders/magazine#:~:text=The%20high%20comorbidity%20of%20Substance,implies%20common%20or%20intersecting%20mechanisms.
10. https://www.niaaa.nih.gov/health-professionals-communities/core-resource-on-alcohol/neuroscience-brain-addiction-and-recovery
11. https://www.psychiatrictimes.com/view/cannabis-induced-psychosis-review
12. https://www.verywellmind.com/co-occurring-disorders-mental-health-and-addiction-4158280#:~:text=Comorbidity%20refers%20to%20the%20fact,mental%20health%20issue%20as%20well.
13. https://pubmed.ncbi.nlm.nih.gov/34396552/
14. https://newsroom.northumbria.ac.uk/pressreleases/researchers-urge-uk-governments-to-tackle-serious-mental-health-illness-and-substance-use-3348394

https://www.rethink.org/advice-and-information/living-with-mental-illness/physical-health-and-wellbeing/drugs-alcohol-and-mental-health/#:~:text=If%20you%20use%20alcohol%20or,illness%20for%20the%20first%20time