About This Page
This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- Mental Capacity Act 2005: 5 statutory principles — start from the PRESUMPTION of capacity
- Capacity is decision-specific and time-specific — a patient may lack capacity for one decision but have it for another
- Two-stage test: 1) Impairment of mind or brain? 2) Does it cause inability to make THIS decision? (understand, retain, weigh, communicate)
- If lacking capacity: decide in patient's BEST INTERESTS (not what the doctor thinks is best medically, but holistic — wishes, values, beliefs, feelings)
- Children: under 16 → Gillick competence (Fraser guidelines for contraception). 16–17 → presumed competent (Family Law Reform Act)
- Valid consent requires: capacity + voluntariness + sufficient information. Consent can be withdrawn at any time
Overview
The Mental Capacity Act 2005 (MCA) provides the legal framework for England and Wales for assessing capacity and making decisions for individuals who lack capacity. It applies to all people aged 16 and over. The Act enshrines five statutory principles, places a presumption of capacity on every adult, and establishes that any decision made on behalf of a person lacking capacity must be in their best interests. Valid consent is the cornerstone of ethical medical practice — treatment without valid consent constitutes battery (in criminal law) or trespass to the person (in civil law), regardless of clinical benefit.
Epidemiology
Capacity assessment is one of the most frequently performed medico-legal tasks in clinical practice. Studies suggest capacity is impaired in approximately 30–40% of medical inpatients and up to 60% of psychiatric inpatients. Conditions commonly affecting capacity include dementia, delirium, severe mental illness (psychosis, mania), learning disabilities, acquired brain injury, and acute intoxication. Importantly, a diagnosis alone does NOT determine capacity — assessment must be functional and decision-specific.
Clinical Features
Symptoms
Patient unable to understand relevant information about the proposed treatment
Patient unable to retain information long enough to make the decision
Patient unable to weigh information (risks vs benefits) as part of the decision-making process
Patient unable to communicate the decision by any means
Fluctuating capacity (e.g. delirium — capacity may vary hour to hour)
Signs
Evidence of an impairment of the mind or brain (diagnostic threshold — stage 1 of MCA test)
Functional inability linked to the impairment (causal nexus — stage 2)
The decision must be assessed at the time it needs to be made
Unwise decisions do NOT equate to lack of capacity — a capacitous adult may make decisions others disagree with
Investigations
First-line
Functional capacity assessmentTwo-stage MCA test: Stage 1 — does the patient have an impairment of mind or brain? Stage 2 — does this impairment mean they cannot understand, retain, weigh, or communicate the relevant information for THIS specific decision?
Clear documentationRecord the assessment in detail: what was explained, how the patient responded, specific areas of difficulty, and the conclusion with reasoning
Second-line
Cognitive screeningMMSE, AMT, MoCA — may support assessment but do NOT replace functional capacity testing
Review of previous documentationAdvance decisions (advance directives), lasting power of attorney (LPA), DNAR/ReSPECT forms
Specialist
Psychiatry or neuropsychology assessmentIf capacity assessment is complex, contested, or high-stakes (e.g. refusing life-saving treatment)
Court of ProtectionFor particularly complex or contested decisions — can appoint a deputy or make a specific decision
1
5 Statutory Principles of the MCA
- 1. Presumption of capacity — every adult (≥16) is presumed to have capacity unless demonstrated otherwise
- 2. Supported decision-making — all practicable steps must be taken to help someone make their own decision before concluding they lack capacity
- 3. Unwise decisions — a person is not to be treated as unable to make a decision merely because they make an unwise decision
- 4. Best interests — any act or decision made on behalf of someone lacking capacity must be in their best interests
- 5. Least restrictive option — any intervention must be the least restrictive of the person's rights and freedoms
2
If patient HAS capacity
- Respect their decision — even if it is unwise, self-harmful, or against medical advice
- A competent adult may refuse any treatment including life-saving treatment (e.g. blood transfusion)
- Document the discussion, ensure the patient has sufficient information, and that the decision is voluntary
- Exception: compulsory treatment under the Mental Health Act 1983 (for mental disorder only, not physical treatment)
3
If patient LACKS capacity
- Decide in their BEST INTERESTS — holistic assessment considering: past and present wishes, beliefs, values, feelings; views of family/carers; advance decisions; LPA
- Best interests is NOT simply "what is medically best" — it encompasses the patient's personal values and preferences
- Consult: family, carers, LPA holder, IMCA (Independent Mental Capacity Advocate) if no one else to consult
- Advance decision to refuse treatment: legally binding if valid and applicable (must be written + witnessed for life-sustaining treatment)
- LPA for health and welfare: the attorney can make health decisions if the patient lacks capacity
- Emergency treatment: may treat without consent if immediately necessary to save life (doctrine of necessity)
4
Children and young people
- Under 16: may consent if Gillick competent (understands what is proposed and its implications)
- Fraser guidelines: specific to contraception/sexual health — competence + best interests + failure to dissuade from activity
- 16–17: presumed competent to consent (Family Law Reform Act 1969). BUT refusal can be overridden by person with parental responsibility or the court
- Under 18: refusal of treatment can potentially be overridden (unlike adults) — court involvement may be needed
Complications
- Treating without valid consent: Battery (criminal) or trespass to the person (civil). Even well-intentioned treatment without consent is unlawful
- Failing to treat a patient who lacks capacity: Negligence if treatment is in best interests and omitted
- DoLS (Deprivation of Liberty Safeguards): If a person lacking capacity is deprived of liberty (e.g. in hospital or care home), authorisation must be obtained via the supervisory body. Being replaced by Liberty Protection Safeguards (LPS)
- Disputes: If family or clinical team disagree about best interests — escalate to clinical ethics committee, mediation, or Court of Protection
UKMLA Exam Tips
- 1A patient with capacity can refuse ANY treatment — even life-saving. You cannot override their decision. This is the single most important principle
- 2Capacity is DECISION-SPECIFIC and TIME-SPECIFIC. A patient with dementia may have capacity for simple decisions but not complex ones
- 3Making an UNWISE decision does NOT mean someone lacks capacity — this is MCA principle 3 and a classic exam trap
- 4The two-stage test: 1) impairment of mind/brain? 2) does it prevent understanding, retaining, weighing, or communicating? Must fail on BOTH stages
- 5Best interests: NOT just medical best interests — must consider wishes, values, beliefs, and feelings of the patient
- 6Gillick competence applies to under 16s. A child can CONSENT if competent, but REFUSAL can be overridden (unlike adults)
- 7Advance decision refusing life-sustaining treatment must be: written, signed, witnessed, and state "even if life is at risk"
- 8Mental Health Act allows compulsory treatment of MENTAL disorder only — you cannot use it to treat physical conditions without consent
practicetest your knowledge on capacity and consentApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — ethics & law and beyond.
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