What you'll learn

• What the interactionist approach means in schizophrenia.
• How the diathesis-stress model explains why some people develop schizophrenia and others do not.
• Key research evidence, especially Tienari et al. (2004).
• How interactionist thinking affects treatment, including combining antipsychotics with psychological therapies.

The starting point: one explanation is rarely enough

In schizophrenia, you have already met biological explanations such as genes and dopamine, and psychological explanations such as family dysfunction and cognitive explanations.

The interactionist approach says we should not treat these as rivals where only one can be right. Instead, schizophrenia is best understood as the result of biological, psychological and social factors working together.

This matters because schizophrenia is complex. For example, someone may inherit a genetic risk, but never develop schizophrenia. Another person may experience severe life stress, but also never develop it. The interactionist approach explains this by saying risk depends on the combination of vulnerability and stress.

Diathesis-stress model

The best-known interactionist explanation of schizophrenia is the diathesis-stress model.

A simple version is:

• Diathesis only: the person is vulnerable, but symptoms may not appear.
• Stress only: the person experiences pressure, but may not develop schizophrenia if they have low vulnerability.
• Diathesis plus stress: the combined risk may pass a threshold and trigger schizophrenia.

Meehl’s original version

One early version was proposed by Meehl (1962). He suggested that a single “schizogene” created a biological vulnerability to schizophrenia. This vulnerability produced a schizotypic personality, meaning the person might show unusual thinking, social withdrawal or odd beliefs.

According to Meehl, schizophrenia would only develop if this genetic vulnerability was combined with stress, such as a highly disturbed family environment.

Today, psychologists no longer accept the idea of one single “schizogene”. Modern genetic research suggests schizophrenia is polygenic, meaning many genes each contribute a small amount of risk.

The modern diathesis-stress model

The modern version is broader than Meehl’s original model.

A diathesis does not have to be purely genetic. It could include:

• Genetic vulnerability, such as having a close biological relative with schizophrenia.
• Neurodevelopmental vulnerability, such as abnormal early brain development.
• Psychological vulnerability, such as childhood trauma or insecure attachment.
• Cognitive vulnerability, such as poor coping strategies or dysfunctional thinking patterns.

Stress can also be biological, psychological or social. Examples include:

• Cannabis use, especially high-potency cannabis.
• Major life events, such as bereavement or relationship breakdown.
• High levels of family criticism or hostility.
• Urban stress, poverty, discrimination or social isolation.

Evidence for the interactionist approach

Twin and family evidence

Biological evidence supports the idea of vulnerability. Gottesman (1991) reviewed twin studies and found higher concordance rates for schizophrenia in identical twins than non-identical twins.

If schizophrenia were entirely genetic, identical twins would have a concordance rate of 100%. They do not. This supports an interactionist explanation: genes matter, but environment also matters.

Tienari et al. (2004)

A key piece of evidence comes from Tienari et al. (2004), a Finnish adoption study.

The researchers studied children whose biological mothers had schizophrenia. These children were adopted into different families, some healthier and some more disturbed in their communication patterns. The children were more likely to develop schizophrenia-related symptoms if they had both:

• a biological genetic risk, and
• an adoptive family environment with high levels of dysfunction or communication deviance.

This is strong support for the diathesis-stress model because it separates biological inheritance from the rearing environment.

There are ethical issues in this kind of research. Adoption and mental health data are highly sensitive, so researchers must protect confidentiality. Participants also need informed consent, careful debriefing, and protection from psychological harm, especially if findings imply family risk or family dysfunction.

Trauma and cannabis evidence

Research also supports the role of environmental stressors. For example, Varese et al. (2012) found that childhood trauma was associated with an increased risk of psychosis. Cannabis use has also been linked to increased risk, particularly when use begins young and involves high-potency forms.

However, these findings are not always simple. People who are already vulnerable may be more likely to use cannabis or experience social difficulties, so it can be hard to prove clear cause and effect.

Evaluation of the explanation

Strength: it is more holistic

The interactionist approach is a strength because it avoids being too reductionist. A purely biological explanation may ignore family stress, trauma and social context. A purely psychological explanation may ignore genetic and neurological vulnerability.

The interactionist model gives a more complete account by combining levels of explanation.

Strength: it explains individual differences

Not everyone with a family history develops schizophrenia. Not everyone who experiences trauma develops schizophrenia. The diathesis-stress model explains this by suggesting that people differ in vulnerability and in the amount of stress needed to cross the threshold.

This is especially useful for AO2 scenario questions, where you may be asked to explain why one person develops symptoms while another does not.

Strength: it has useful treatment implications

The model has real-world value because it suggests treatment should also be interactionist. If schizophrenia involves biological vulnerability and psychological stress, then treatment should target both.

This supports the use of:

• Antipsychotic medication to reduce symptoms such as hallucinations and delusions.
• Cognitive behavioural therapy for psychosis, often called CBTp, to help the person manage beliefs and distress.
• Family therapy to reduce relapse risk by lowering criticism, hostility and emotional over-involvement.

This fits with NICE guidance, which recommends antipsychotic medication alongside psychological interventions such as CBTp and family intervention.

Limitation: the model can be vague

A weakness is that “diathesis” and “stress” can mean many different things. If almost anything can count as a vulnerability and almost anything can count as a stressor, the model becomes difficult to test precisely.

For example, one researcher might define stress as family conflict, while another defines it as cannabis use or urban poverty. This makes it harder to produce one clear, measurable theory.

Limitation: measuring stress is difficult

Stress is often measured using interviews or self-report questionnaires. These can be affected by memory errors, social desirability or interpretation. For instance, someone may under-report cannabis use or may not remember early childhood adversity accurately.

This creates methodological problems because the model depends on accurately identifying both vulnerability and stress.

Limitation: risk of blaming families

The interactionist approach can accidentally lead to family blame, especially when discussing expressed emotion or dysfunctional communication. This is ethically sensitive. Families may already be under stress and may feel blamed for causing schizophrenia.

A balanced exam answer should make clear that family stress may contribute to relapse risk, but it is not a simple cause and does not mean families are responsible for the disorder.

Interactionist treatment

The interactionist approach is important not only for explaining schizophrenia, but also for treating it.

A biological approach alone might recommend antipsychotic drugs. A psychological approach alone might recommend CBTp or family therapy. An interactionist approach argues that combined treatment is often better because it targets multiple causes and maintaining factors.

Antipsychotic medication

Antipsychotics are drugs used to reduce psychotic symptoms, especially hallucinations and delusions. They are usually linked to dopamine activity in the brain.

Medication may reduce symptom intensity, making it easier for the person to engage with therapy. However, medication can have side effects, and some people discontinue treatment.

CBTp

CBTp helps people make sense of symptoms and reduce distress. It does not necessarily remove hallucinations, but it can help a person challenge unhelpful interpretations. For example, someone who hears a voice may learn to question whether the voice really has power over them.

Family therapy

Family therapy aims to reduce relapse by improving communication and lowering expressed emotion.

High expressed emotion is linked with relapse, so family therapy can help relatives respond in calmer and more supportive ways.

Evidence for combined treatment

Research generally supports combining biological and psychological treatments. Pharoah et al. (2010) reviewed family intervention studies and found that family therapy can reduce relapse and improve medication adherence, although results varied between studies.

Jauhar et al. (2014) found CBTp had only a modest effect on symptoms, which suggests psychological therapy is useful but not a complete replacement for medication.

This supports an interactionist treatment approach: medication and therapy may each help, but in different ways.

How to turn this into an essay

For AO1, describe the model clearly:

• Schizophrenia results from an interaction between vulnerability and stress.
• Vulnerability can be genetic, biological or psychological.
• Stress can include trauma, cannabis, family dysfunction or life events.
• Symptoms emerge when combined risk passes a threshold.
• Treatment should combine biological and psychological therapies.

For AO3, evaluate using evidence and implications:

• Twin research supports genetic vulnerability but not genetic determinism.
• Tienari et al. supports gene-environment interaction.
• The model is holistic and explains individual differences.
• The model can be vague and difficult to test.
• It has real-world treatment value but may risk blaming families.