How to Know If You Have Depression: What the Signs Actually Mean

What we checked before telling you this

Depression is one of the most studied conditions in medicine, which means there's a lot of high-quality evidence to draw on — and also a lot of noise, myth, and oversimplification to cut through. We cross-referenced the DSM-5 diagnostic criteria with large-scale epidemiological research, reviewed the clinical validation data behind commonly used screening tools, examined meta-analyses on how often depression is missed or misidentified, and looked at what general practitioners actually recommend as a first step when a patient presents with these concerns. We prioritised sources that examined real-world clinical outcomes over opinion-based guidance.

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  DSM-5 diagnostic criteria reviewed The American Psychiatric Association's criteria require at least five of nine specific symptoms, present most of the day nearly every day for at least two weeks, causing significant impairment — this is the clinical standard against which all diagnosis is measured.
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  PHQ-9 validation evidence confirmed The Patient Health Questionnaire-9 has been validated in dozens of studies across primary care settings, with a score of 10 or above showing sensitivity of 88% and specificity of 88% for major depressive disorder — making it the most evidence-supported free screening tool available.
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  Physical mimics of depression identified Research confirms that hypothyroidism, vitamin D deficiency, B12 deficiency, iron-deficiency anaemia, and sleep apnoea can all produce symptoms clinically indistinguishable from major depression — ruling these out before assuming a psychiatric diagnosis is essential, not optional.
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  Evidence on treatment options assessed Meta-analyses confirm that structured exercise, CBT, and antidepressant medication each have meaningful evidence bases for different severity levels — and that doing nothing while waiting to feel better is itself a high-risk approach, as untreated depression is associated with a worsening trajectory in the majority of cases.

There's more than one right path — here's how to choose yours

The right first move depends on how you're feeling right now, how long it's been going on, and how much it's affecting your day-to-day life. Here's what the evidence actually supports at each stage.

What people try first that doesn't actually help

When you're not feeling like yourself, it's tempting to reach for the most available fix, or to wait and see. These are the approaches most likely to delay real help without delivering real benefit.

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  Waiting it out and hoping it passes — Ordinary low moods do pass; clinical depression typically does not resolve on its own without intervention. Research on untreated depression shows that the majority of untreated episodes last six months or longer, and repeated episodes tend to become more severe and more frequent over time. Waiting is itself a choice with consequences.
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  Self-diagnosing from symptom checklists alone without professional input — Symptom overlap between depression, anxiety disorders, burnout, hypothyroidism, ADHD, and grief is substantial — a checklist can tell you something is wrong, but it cannot tell you what. Treating the wrong thing delays treating the right thing, and several physical conditions that mimic depression require completely different interventions.
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  Starting with supplements (St. John's Wort, omega-3s, etc.) as a first-line treatment — St. John's Wort has some evidence for mild depression but interacts dangerously with a long list of common medications including contraceptives, anticoagulants, and antiretrovirals — taking it without telling your GP is risky. Omega-3s have weak and inconsistent evidence as a standalone treatment. Neither replaces a clinical diagnosis, and both can give you a false sense of having done something meaningful.
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  Using alcohol to manage low mood — Alcohol is a central nervous system depressant. The temporary relief it provides is real but short-lived, and the rebound effect — including disrupted sleep, increased anxiety, and worsened mood the following day — directly amplifies depressive symptoms. Heavy alcohol use is both a common response to depression and one of the most reliable ways to make it worse.