Diagnosis
Five or more symptoms for two weeks, including at least one of depressed mood or anhedonia, causing functional impairment:
Sleep change, loss of Interest, Guilt or worthlessness, loss of Energy, poor Concentration, Appetite or weight change, Psychomotor change, Suicidal ideation.
Before settling on the diagnosis, exclude:
- Bipolar disorder — always ask about past manic or hypomanic episodes. Starting an antidepressant in undiagnosed bipolar disorder can precipitate mania, and this is a favourite stem
- Medical causes — hypothyroidism, anaemia, B12 deficiency, sleep apnoea, Parkinson's, malignancy
- Substances — alcohol, stimulant withdrawal; drugs such as interferon, isotretinoin, corticosteroids
- Grief, which is distinguished by preserved self-worth and waves of sadness tied to the loss
Treatment
- Mild to moderate: psychotherapy — CBT or interpersonal therapy — is as effective as medication
- Moderate to severe: an antidepressant plus psychotherapy beats either alone
- First-line drugs: SSRIs, SNRIs, bupropion, mirtazapine. Choose on side-effect profile and comorbidity rather than efficacy, which is broadly similar
Practical points that get examined:
- Allow 4–6 weeks at an adequate dose before judging response
- Continue for at least 6–12 months after remission; longer with recurrent episodes
- Taper on stopping — abrupt cessation causes a discontinuation syndrome, especially with paroxetine and venlafaxine
- Serotonin syndrome when combined with triptans, tramadol, linezolid or MAOIs: clonus, hyperreflexia, hyperthermia, agitation
- Hyponatraemia with SSRIs, particularly in older patients
- Sexual dysfunction is common and a major reason for non-adherence — ask about it
- ECT for severe depression with psychosis, catatonia, refusal to eat and drink, or high suicide risk. It is the most effective treatment available, not a last resort
Suicide risk assessment
Ask directly. Asking about suicide does not plant the idea — this is explicitly tested.
Work through: ideation → intent → plan → means → preparatory acts (giving away possessions, writing a note, putting affairs in order).
Static risk factors: previous attempt — the strongest single predictor — male sex, older age, Indigenous identity in the Canadian context, chronic pain or illness, family history.
Dynamic and modifiable: current psychiatric illness, substance use, hopelessness, recent loss, access to means, social isolation.
Protective: strong social support, dependent children, religious or cultural beliefs, engagement with care, future orientation.
Disposition
Voluntary admission where the patient agrees and risk is high. Where they do not, involuntary admission under the provincial Mental Health Act requires a mental disorder plus risk of harm to self or others, or inability to care for oneself — the exact criteria and form numbers vary by province, but the principle is the same.
Restricting access to means — firearms, stockpiled medication — is a concrete intervention with good evidence, and belongs in the answer.