Reasoning GP · Algorithm · 1-page summary
Low mood — new presentation in adults
For: adults presenting with low mood in primary care. Not for: under 18s (CAMHS, NICE NG134). Pregnant or within a year of birth: use the perinatal routes in blocks 0–2.
Core rule: ask about suicidal thoughts directly and screen for past mania before any antidepressant. Use the conversation, not a score or a low/medium/high label, to plan safety.
0Stop — call 999 now — before any history
- Overdose taken, serious self-injury or attempt in progress → 999 — do not wait for symptoms after an overdose
- Immediate danger to life from suicidal intent → 999
- Postpartum psychosis with risk to self or baby → 999 or crisis team
1Triage — what kind of low mood
| Picture | First move |
|---|---|
| Low mood 2+ weeks | Depression likely: grade severity (PHQ-9 under 16 less severe; 16 or over more severe) with judgement |
| Past highs | Possible bipolar depression — specialist advice; no antidepressant alone |
| After a loss | Grief or adjustment — support and review |
| Pregnancy to 1 year | Perinatal — check warning signs (block 2) |
| Older adult | Consider dementia, delirium and medicines |
2Screen — one row is enough
- Suicidal intent, a plan, or unable to stay safe → crisis team Same-day (NHS 111 option 2 out of hours)
- Psychotic symptoms or severe self-neglect, not eating or drinking → Same-day
- Possible mania: little need for sleep, pressured speech, grandiosity, risk-taking → Same-day if acute or at risk
- Perinatal warning signs: rapid change, violent self-harm thoughts, estrangement from the baby → perinatal team Same-day
- Safeguarding: children or dependants at risk, domestic abuse → Same-day local procedures
- Older adult with acute confusion → delirium Same-day
3Assess — targeted, not blanket
☐ Mood, anhedonia, associated symptoms, function ☐ Thoughts, intent, plan, means, previous self-harm, protective factors ☐ Mania screen, family history ☐ AUDIT-C, drugs, medicines review ☐ Mental state, weight, pulse, BP
Bloods by indication: TSH, FBC + ferritin, B12 + folate, HbA1c, U&E, LFTs, calcium. Sodium if older; ECG before citalopram or escitalopram with cardiac risk.
PHQ-9 measures severity — item 9 is not a risk assessment.
4Classify — only if the screen is negative
- Less severe depression — guided self-help or group CBT/behavioural activation via Talking Therapies.
- More severe depression — offer individual CBT plus an antidepressant.
- Grief or adjustment — support, bereavement services, review in 2–4 weeks.
- Alcohol or drug-related — brief intervention; mood often lifts within weeks of stopping.
- Organic or drug-induced — hypothyroidism, anaemia, B12, OSA, culprit medicines → treat the cause.
- Uncertain — say so, keep the safety plan, review in 2 weeks.
5Treat today — doses: NICE/SPC, BNF, local formulary
- Less severe: do not routinely offer an antidepressant first-line unless the person prefers it.
- If starting: an SSRI — sertraline usual adult dose 50 mg once daily. Warn: 2–4 weeks to work, early agitation, possible early suicidal thoughts (same-day contact), do not stop suddenly.
- Overdose risk: limited quantities (1–2 weeks); avoid tricyclics.
- Today: written safety plan, crisis numbers in the phone, Talking Therapies self-referral, fit note if needed.
6Refer routinely
- Suspected bipolar without acute risk → specialist assessment Urgent.
- Moderate or severe perinatal illness → perinatal mental health (CG192).
- Older adult with cognitive impairment → memory service. Under 18 → CAMHS.
- Alcohol or drug services; bereavement support; social prescribing; debt advice.
7Never reassure by
- A low score on a risk tool or "no plan".
- A PHQ-9 item 9 of zero.
- Starting an SSRI without asking about past highs.
- "It is just grief" when symptoms keep deepening.
- Calling it depression in an older adult before considering delirium and dementia.
- Assuming low mood in pregnancy or after birth is the baby blues after 2 weeks.
8Safety-net — say it, then document it
999 “Call 999 if you have taken an overdose, injured yourself seriously, or are in immediate danger.” Same-day “If the thoughts get stronger, you make a plan or you feel you can’t keep yourself safe, call the crisis line or NHS 111 option 2 today. Tell us the same day if you feel agitated after starting the tablet, or high with little need for sleep.”
Follow-up: 1 week after starting an antidepressant if aged 18–25 or at increased risk; otherwise 2 weeks; no drug started → 2–4 weeks with repeat PHQ-9.
✓Safe to leave primary care only if — all five, documented
No block 0–2 row applies
Suicide and mania asked about directly
Physical causes and medicines considered
Plan agreed: Talking Therapies ± SSRI
Safety plan given; review booked
Summary of the full Reasoning GP low mood algorithm, which holds the detail, examination, investigations and evidence. Sources: NICE NG222, NG225, CG192, CG185, NG134; MHRA; sertraline SPC. Clinical reference — follow local pathways and check doses in the current SPC, BNF and local formulary.