Addiction is not just about reward.

It reflects predictable dysfunction across brain systems governing behaviour, learning, and control.

Here are 5 core neurobiological processes underlying addiction and relapse: 🧵👇

(Click through to see all 5) 1/ Reward & Motivation

Chronic substance use floods the brain with dopamine, eventually downregulating D2 receptors.

This structurally shifts the brain from "liking" the drug (hedonic pleasure) to intensely "wanting" it (incentive salience).

The biological urge to use becomes overpowering, even when the substance ceases to provide actual pleasure.

Educating patients that the craving they feel is a structural reflex, not a reflection of character, relieves guilt and contextualises relapse.

More than 50% of patients with schizophrenia smoke tobacco. [Fond et al 2017]; [Dickerson et al 2018]; [Oluwoye et al 2019]

Despite heavily substantiated nicotine-induced metabolic and pharmacokinetic risks, this number refuses to drop.

This raises the question: “What does nicotine do that makes this specific patient population so uniquely dependent on it?”

Here’s a neurobiological breakdown of nicotine dependence in schizophrenic patients clinicians should know: 🧵👇 The Intrinsic Receptor Deficit

In the general population, chronic smoking leads to an upregulation of α4β2 nicotinic receptors.

In schizophrenia, this compensatory upregulation is impaired.

This suggests an intrinsic defect in the nicotinic receptor system. 

Theoretically, for schizophrenia patients, smoking is an attempt to achieve receptor saturation to overcome this deficit, though it rarely leads to sustained cognitive improvement.

Depression is not a single, uniform brain pattern.

It does not present the same way in every patient.

Sometimes it appears as rumination.
Sometimes as cognitive dysfunction.
Sometimes as emotional over-reactivity.

So how do we make sense of what’s happening beneath the surface? There is a structured way to approach this.

Here is a clinical breakdown of the Triple Network Model, a framework for understanding functional brain changes in depression 🧵👇 The Triple Network Model frames depression as dysregulation within and between three major functional brain systems.

Rather than locating the disorder in one isolated region, it conceptualises depression as a disturbance in large-scale network organisation.

This gives clinicians a more structured way to think about why depressive presentations can differ so markedly.

PTSD treatment is not just about reducing symptoms.

The other half of the clinical equation is about interrupting the mechanisms that make the brain increasingly reactive over time.

To do so, there are 2 clinical PTSD concepts clinicians must take into full consideration in treatment planning: 🧵👇 PTSD develops through a combination of psychological and biological mechanisms.

This dual foundation also means that effective treatment must address both sides of the disorder, often integrating psychotherapy with pharmacotherapy.

This is where the following concepts come in, illustrating exactly what is happening in the dysregulated brain, helping clinicians align their intervention strategies with the underlying pathology.

For decades, Major Depressive Disorder (MDD) has been clinically framed primarily through mood symptoms.

However, recent clinical studies have described a potential emerging biotype of MDD whose core pathology leans more towards cognition than just mood symptoms.

Here are 5 key clinical insights clinicians need to know about this emerging cognitive MDD biotype:🧵👇 Cognition has long been recognised as part of MDD, with impairments in areas such as attention, working memory, and processing speed already linked to poorer function and poorer treatment outcomes.

Even so, MDD remained primarily organised around mood symptoms, with cognitive dysfunction often treated as secondary rather than defining.

This emerging cognitive biotype shifts that framing by suggesting that, in some patients, cognition may be more central to the pathology itself.

Addiction vulnerability is heritable.

While often framed as a brain reward-system dysfunction, clinical studies suggest that genetic factors are estimated to account for around 40-60% of addiction risk, with inherited vulnerability contributing to susceptibility. [Volkow et al., 2019]

This raises the next question: How does inherited risk translate into biological vulnerability, and what does that mean in clinical practice?🧵👇 The Polygenic Architecture of Vulnerability

What is inherited is not addiction itself, but vulnerability.

This vulnerability is polygenic: multiple variants, especially in dopamine and glutamate systems, increase susceptibility.

In effect, what is inherited may be a reward-system profile prone to dysregulated reinforcement.

This may explain why some individuals show greater neurobiological vulnerability even before substance exposure.

Around 70% of adults globally experience at least one traumatic event, with a proportion of individuals subsequently developing PTSD. [Benjet et al., 2016]

However, standard clinical approaches to PTSD remain largely binary: patients either meet the symptom checklist, or they don't. 

But what if underlying pathological processes begin long before the DSM checklist is met? 

To bridge this gap, here’s a 5-stage clinical staging approach to PTSD clinicians can apply in practice:🧵👇 Stage 0: Trauma Exposed & Asymptomatic

Before clinical diagnosis, neurobiological changes associated with trauma exposure may begin to emerge. 

Trauma exposure has been associated with alterations in glucocorticoid receptor sensitivity, circadian regulation, and amygdala reactivity. 

Clinically, individuals may exhibit transient attention bias and deficits in extinction learning.

This is the "watch-and-wait" phase, where early resilience strategies may be highly beneficial.

Depression is often treated as a single disorder.

But clinically, not all depression is the same.

Different subtypes have distinct symptom profiles, biology, and treatment responses.

Here are 3 key depressive subtypes clinicians should recognise 👇🧵 In clinical practice, depressive presentations can show distinct subtype patterns that carry different treatment implications.

Recognising these patterns helps clinicians move beyond a generic diagnosis of major depressive disorder and toward a more targeted formulation.

Three commonly recognised depressive subtypes include:

ADHD is rarely “just ADHD.”

Up to 90% of adults with ADHD have at least 1 comorbid psychiatric condition.

These overlapping presentations can mimic ADHD, hide it, or distort the diagnosis entirely. 🧵👇 ADHD comorbidity is not the exception. It is the rule.

And without a structured assessment model, clinicians can easily:

 • misattribute symptoms
 • miss key differentials
 • overdiagnose ADHD
 • overlook the primary driver of impairment

If Fear of Crowds Points to Either SAD or Agoraphobia... How Can You Tell Which is Which?

Clinically, both Social Anxiety Disorder (SAD) and agoraphobia look nearly identical on the surface.

Patients avoid busy spaces, isolating themselves.

However, confusing one for the other means risking the implementation of the wrong clinical intervention.

Here’s how to map the SAD-Agoraphobia threat model in practice: 🧵👇 Fear of crowds can sit under either SAD or agoraphobia.

However, the core discriminator between the 2 is the threat model:

SAD → fear of scrutiny and negative evaluation (embarrassment, looking stupid, being judged).

Agoraphobia → fear of physical/mental harm in that setting (panic-like symptoms, losing control, being unable to escape/get help).

Same crowd, different feared outcome.

Is it really treatment-resistant depression?

Current pharmacological treatments for depression have largely been developed around the monoamine deficiency hypothesis.

But depression is a complex disorder with heterogeneous features and frequent mental and somatic comorbidity.

Here’s what clinicians should know about the limits of a largely monoaminergic approach. 🧵👇 Current antidepressant treatments largely focus on 'improving' monoaminergic transmission.

This led to the development of:

• MAOIs
• TCAs
• SSRIs
• SNRIs
• newer agents such as vortioxetine and agomelatine

Despite widespread use, existing treatments have important drawbacks including delayed onset of efficacy, treatment resistance, and tolerability issues.

Why Do Intrusive Memories in PTSD Feel So Real?

PTSD is not simply a psychological reaction to trauma; it is a stressor-induced alteration of one's neurocircuitry. 

Clinical data shows that in PTSD, there is an overactivation of "Fear-On" circuits and a suppression of "Fear-Off" circuits in the amygdala, rendering the intrusive memories patients experience to feel as real as how they first went through it.

Here is a neurobiological breakdown of why intrusive memories in PTSD feel so real:🧵👇 In PTSD, intrusive memories feel “real” because limbic threat circuits remain hyperactive even when no objective danger is present.

Amygdala overactivity continues to signal danger when trauma cues or internal reminders appear, and fear networks show persistent hyperexcitability.

This re-evokes full autonomic and affective responses as if the event were happening in real time, even in objectively safe environments, contributing to vivid re-experiencing and flashbacks.

How Do Antipsychotics Induce Metabolic Dysfunction?

Most assume that weight gain is the only side-effect of taking antipsychotics.

However, clinical data reveal that these agents also induce metabolic dysfunction, both directly and indirectly, by increasing blood glucose independent of adiposity and leading to uncontrolled lipolysis via adipose tissue dysregulation.

Here's a breakdown of how antipsychotics may induce metabolic dysfunction and what clinicians can do about it in practice:🧵👇 Antipsychotic-induced weight gain may lead to insulin resistance when adipose tissue reaches a point of decreased lipid storage capacity.

This loss of storage integrity may induce uncontrolled lipolysis and increased free fatty acids in the circulation (lipotoxicity).

These acids flood the liver, stimulating gluconeogenesis (making new sugar).

The liver becomes overwhelmed, and the muscles stop absorbing glucose efficiently, setting the stage for systemic insulin resistance.

Why Are Substance Use Disorders (SUDs) Common in Borderline Personality Disorder (BPD) Patients?

Most assume that substance use in BPD is merely a secondary coping mechanism for acute emotional distress.

However, with a reported lifetime prevalence of 78%, clinical data suggest that specific neurocognitive deficits like high trait impulsivity and altered reward processing, are associated with this high comorbidity frequency.

Here is a breakdown of the mechanisms linking BPD to SUDs: 🧵👇 BPD is fundamentally characterised by high trait impulsivity as a primary core diagnostic criterion in the DSM-5 clinical framework.

This specific trait makes rapid and unplanned engagement in psychoactive substance use behaviour significantly more likely for patients with BPD.

Then, this inherent deficit in impulse control reduces the patient's capacity to inhibit or moderate use, significantly increasing the likelihood of progressing to an established SUD over time.

Can Prolonged Lithium Therapy Contribute to Chronic Kidney Disease (CKD)?

While lithium remains the gold standard for mood stabilisation, chronic exposure carries a cumulative risk of progressive renal dysfunction.

Existing clinical data indicate that prolonged lithium exposure can disrupt distal tubular homeostasis, leading to a specific tubulointerstitial pathology that may progress to irreversible CKD.

Here’s what clinicians need to know about the lithium-CKD link:🧵👇 Lithium-induced CKD begins when lithium enters the principal cells of the collecting duct via ENaC channels.

Once intracellular, it inhibits Glycogen Synthase Kinase-3 beta (GSK-3β).

This enzymatic blockade disrupts the regulation of water transport, initiating the cellular stress response that underpins chronic renal impairment.

Can Low Iron Levels Exacerbate ADHD?

Most view ADHD primarily as a neurodevelopmental deficit in dopaminergic transmission.

However, clinical data suggests that for a subset of patients, the pathology is aggravated by an often overlooked metabolic variable: systemic iron deficiency.

Low peripheral iron levels do not just cause anaemia; it also alters the brain’s ability to synthesise the neurotransmitters required for focus.

Here’s a breakdown of how low iron levels can exacerbate ADHD: 🧵👇 The primary mechanism linking low iron to ADHD involves the enzymatic production of dopamine.

Iron acts as a critical cofactor for tyrosine hydroxylase, the rate-limiting enzyme in the catecholamine synthesis pathway.

When ferritin levels are insufficient, the brain cannot maintain adequate dopamine synthesis.

This creates a functional dopamine deficit that mirrors or intensifies the core executive dysfunction seen in ADHD.

Why Do Antidepressants Often Underperform in Borderline Personality Disorder (BPD)?

In real-world practice, BPD is frequently treated with antidepressants.

Yet major guidelines and evidence reviews consistently show that medication is not recommended for the core symptoms of BPD, and clinical response to antidepressants is often inconsistent.

So why do antidepressants so often fall short in BPD and what should clinicians do? 👇🧵 Antidepressants aren’t ‘designed’ for core BPD pathology

Borderline Personality Disorder is best managed with structured psychotherapy.

Pharmacotherapy is considered adjunctive, used cautiously, and primarily for:

- acute crises, or
- clearly defined comorbid disorders (e.g. major depression, anxiety disorders).

When antidepressants “don’t work” in BPD, this often reflects target mismatch, not illness severity.

Sleep isn’t just “off.”

The locus coeruleus (LC), the brain’s noradrenaline hub, stays active in a patterned way, shaping when we sleep deeply, dream, or wake too easily. (Osorio-Forero 2022)

Here’s why it matters clinically.

1/11🧵 Classic view: LC goes quiet at night.

Revised view: it’s state-dependent.

• NREM: activity is low but rhythmic.
• REM: LC neurons are almost completely silent.

2/11🧵

How Can Dissociation Exacerbate PTSD?

Most view dissociation as a secondary trauma symptom.

However, clinical data suggests it is a maladaptive state that actively increases PTSD severity by denying the brain the opportunity to process traumatic memories (Ozer et al. 2003)

Rather than a temporary homeostatic pause, dissociation is a state of emotional over-modulation linked to poorer prognoses and higher risks of self-harm or suicide.

Here’s a breakdown of how dissociation exacerbates PTSD👇🧵 Dissociation in PTSD is often associated with the emotional overmodulation subtype (PTSD+DS).

In this phenotype, neuroimaging models describe increased top-down regulation of limbic reactivity by medial prefrontal regions, sometimes referred to as the corticolimbic inhibition model (Lanius et al., 2010).

This means traumatic reminders may trigger not hyperarousal, but instead a detached shutdown state, reducing defensive emotional engagement.

Why Is Psychotherapy Often Limited During Active Addiction?

Psychotherapy is essential in addiction care, but during active substance use or acute withdrawal, the brain may be in a state where higher-order cognitive engagement is biologically constrained.

Addiction is not simply a disorder of 'insight'.

It is a disorder of neurocircuitry.

Here’s the neuroscience behind why treatment sequencing matters: 🧵👇 Addiction Impairs Prefrontal Control (“Hypofrontality”)

Chronic substance use is associated with structural and functional disruption in prefrontal regions responsible for:

 • executive function
 • inhibitory control
 • decision-making
 • salience regulation

Imaging studies show reduced metabolic activity in the OFC, ACC, and DLPFC in addiction.

This state is often described as hypofrontality, a compromised capacity for sustained top-down regulation.

Can Smoking Compromise Antipsychotic Efficacy in Schizophrenia?

The interaction between smoking and schizophrenia is complex and multifaceted, with patients consistently showing higher rates of tobacco smoking and heavy nicotine dependence.

One important consideration is the influence smoking has on the CYP450 system.

🧵👇 The isoenzyme CYP1A2 is highly induced by smoking tobacco.

CYP1A2 is the main enzyme involved in the metabolism of the antipsychotics clozapine and olanzapine.