Can a Psychologist Diagnose Mental Illness?

This is a common question. People often wonder if they need to see a psychiatrist (a medical doctor) for a diagnosis, or if a psychologist can provide one. In Australia, registered psychologists – particularly clinical psychologists – have the training and expertise to diagnose many mental illnesses.

Training and Qualifications Matter

All psychologists complete extensive education in mental health. At a minimum, a registered psychologist has six years of training (a four-year university psychology degree plus two years of supervised practice or equivalent postgraduate study). Clinical psychologists, like me, go even further – we complete additional specialist postgraduate training in clinical psychology (usually a Master’s or Doctorate, which is about two more years full-time) focused specifically on assessing, diagnosing, and treating mental disorders. This means a clinical psychologist has advanced skills in identifying a wide range of psychological difficulties. We are also well-versed in diagnostic manuals (like the DSM-5) and evidence-based assessment tools.

What Psychologists Can Diagnose

Psychologists use the same diagnostic criteria that psychiatrists and GPs use for mental health conditions. We can assess whether your symptoms meet the criteria for conditions such as:

• Anxiety Disorders: e.g. Generalised Anxiety Disorder, social anxiety, panic disorder, phobias.
• Depressive Disorders: e.g. Major Depressive Disorder, persistent depression (dysthymia).
• Trauma-Related Disorders: e.g. Post-Traumatic Stress Disorder (PTSD) or Complex PTSD.
• Obsessive-Compulsive and Related Disorders: e.g. OCD.
• Eating or Sleeping Disorders: such as anorexia, bulimia, insomnia (psychologists often work in conjunction with medical doctors on these).
• Personality Disorders: Clinical psychologists can diagnose conditions like Borderline Personality Disorder, etc., typically after thorough assessment.
• Substance Use Disorders: identifying problematic use of alcohol or drugs and any co-occurring mental health issues.

In fact, psychologists are often the first professionals to identify these issues during therapy sessions. We do so through in-depth interviews, questionnaires, and observation of your symptoms and history. For example, if you come in describing persistent worry, sleepless nights, and difficulty concentrating, a psychologist can determine if those symptoms add up to an anxiety disorder and tell you, “It looks like you have Generalised Anxiety Disorder,” or another relevant diagnosis.

What Psychologists Cannot Do

While psychologists can diagnose, there are a few important distinctions:

• Prescribing Medication: Psychologists are not medical doctors, so they cannot prescribe medications (like antidepressants, anti-anxiety meds, etc.). If during the course of therapy a psychologist believes you might benefit from medication, they will refer you to a GP or psychiatrist who can prescribe. Psychologists and psychiatrists often work together in such cases, where the psychiatrist manages the medical side (medication) and the psychologist provides the therapy side.
• Medical Tests: Psychologists do not perform medical examinations or blood tests/brain scans. If there’s a concern that physical health issues could be causing psychological symptoms (for example, a thyroid problem causing depression-like symptoms), a psychologist will suggest you also see a doctor. Psychiatrists, being doctors, can look into those medical aspects directly.
• Severe Mental Illness Management: Psychologists can definitely diagnose conditions like schizophrenia or bipolar disorder, but these conditions typically require medical intervention (medication, possible hospital care) in addition to therapy. A psychologist will usually ensure you are under the care of a psychiatrist or GP for the medical side if you have a major mental illness. They might hold off on providing therapy until the acute phase is managed medically (for instance, they may ask that a condition like bipolar is stabilised with medication before doing intensive therapy, for safety and effectiveness).
• Certain Assessments: Some specialised assessments are outside the scope of what many psychologists offer in private practice. For example, diagnosing ADHD or Autism often requires specific testing and observations (sometimes by neuropsychologists or clinical psychologists who specialise in that area). I note that I don’t offer ADHD or autism assessments in my practice because they require specialised tools and expertise found in certain clinics. So, while a general psychologist might suspect these conditions, they may refer you to a specialist for a formal diagnosis.

The Diagnostic Process in Therapy

If you’re seeing a psychologist, you might be curious if or when they’ll “diagnose” you. It’s important to know that many psychologists don’t rush to label what you’re experiencing, unless having a diagnosis is important for guiding treatment or accessing services. Early on, we’ll focus on understanding your symptoms and story. Over a few sessions, a picture usually emerges of what you’re dealing with.

When a psychologist does identify a likely diagnosis, we will typically discuss it with you. For example, we might say, “From what you’ve described, it sounds like you’re experiencing clinical depression,” and then explain what that means in plain language. You’ll have a chance to ask questions about it. A good psychologist will present a diagnosis as a way to help validate what you’re feeling (“Ah, there’s a name for this and many people experience it”) and to inform the therapy approach – not as a limiting label or a “life sentence.” You are always more than a diagnosis, and it’s just one piece of the puzzle.

In other cases, a psychologist might deliberately avoid focusing on diagnosis if they feel it’s not necessary. Some people come to therapy not fitting a clear category, or with a mix of issues. The psychologist might say, “Whether or not this meets criteria for X disorder, let’s focus on the specific problems you’re having and work on those.” That’s a common approach, because at the end of the day, improving your well-being is the goal – diagnosis is a tool toward that, not the goal itself.

Collaboration with Other Professionals

Psychologists often work hand-in-hand with GPs and psychiatrists. For instance:

• If you have a Mental Health Treatment Plan from a GP (which provides Medicare rebates for psychology sessions), your GP has likely given a preliminary diagnosis (e.g. “Anxiety” or “Depression”) when referring you. The psychologist will do their own assessment as therapy progresses, which might refine or expand on that initial diagnosis.
• If a psychologist feels you need a medication review or psychiatric evaluation, they’ll recommend seeing a GP or psychiatrist. We can even communicate (with your consent) with your doctor to share our observations.
• Conversely, if you were seeing a psychiatrist who diagnosed you and managed your medication, that psychiatrist might refer you to a psychologist for regular talking therapy. The psychologist in that case focuses on therapy, while the psychiatrist focuses on meds, and they might touch base occasionally about your progress (again, with your consent).

Bottom line: Yes, a psychologist can diagnose many mental health conditions and is qualified to do so. In Australia, clinical psychologists especially are recognised by Medicare as experts in assessment and diagnosis of mental disorders. However, a psychologist’s role doesn’t stop at giving a diagnosis – we work with you on treating and managing the issue through therapy. And if your needs go beyond our scope (like needing medication), we will guide you to the appropriate medical resources while continuing to support you in therapy.

If you’re worried you might have a certain condition, a psychologist is actually a great place to start. We can give you clarity on what’s going on mentally and emotionally, and set you on a path toward healing. You’ll get both understanding (the “why” and “what” of your struggles) and tools to cope (the “how” to get better) – which together can be very empowering.