Depression is a common mental illness characterised by low mood which falls outwith the normal and appropriate lowering of mood secondary to negative life events and challenges.


Signs and symptoms

For diagnosis to be made, an individual will have experienced symptoms nearly every day for at least 2 weeks.

The individual’s functioning is significantly impaired, or they are able to function only with significant effort.

Symptoms fall into three categories according to ICD 11 categorisation:

1. Affective symptoms - low mood/irritability (in children), anhedonia (markedly diminished interest or pleasure in activities)

2. Cognitive - impaired concentration/decision making, negative self-perception (low self-esteem or guilt), hopelessness for the future, thoughts of death/suicide 

3. Neuro-vegetative – disrupted sleep, change in appetite/weight, psychomotor agitation/retardation, reduced energy levels 



History taking and mental state examination should be completed alongside physical examination and investigations guided by the clinical picture.

Non-psychiatric causes should always be considered e.g. delirium often involves changes in mood, and there are a number of biochemical abnormalities which can result in low mood (TFTs, Calcium, B12/folate, anaemia, kidney disease etc.).  

Also think - is there another psychiatric diagnosis which fits better? 

  • Alcohol or substance use disorder / Anxiety disorder / Adjustment disorder 
  • Bipolar Affective Disorder (beware as antidepressants can cause mania in this case) 
  • Could there be a Personality disorder – is the picture of low mood chronic with maladaptive care-seeking behaviours 
  • Dementia – always a differential in the elderly 
  • Eating disorder  

Remember also to always consider risk!  

Asking about suicidal thoughts/plans does not increase the likelihood of patients completing suicide – and not asking means that a safe management plan cannot be achieved. See risk assessment section for more details.


  • Consider available/appropriate social supports
  • For mild/moderate depression – CBT has good evidence, as well as other psychological interventions (counselling, interpersonal therapy, behavioural activation) 
  • Antidepressants for moderate/severe depression, or persistent mild depression without improvement from social and psychological interventions alone
  • Part of treatment is managing risk, with appropriate safety-netting for how to contact services, especially out-of-hours if in crisis
  • Consider discussion with Psychiatry if there are concerns about risk, lack of clarity over diagnosis, or if not improving with treatment 

Last reviewed: 21/02/2024

Next review date: 21/08/2024

Author(s): Core Trainee in Psychiatry, NHS Lothian & Medical Education Fellow, NHS Lothian.

Author email(s):

Reviewer name(s): Medical Education Fellow, NHS Lothian.