Mental Health Act or Mental Capacity Act: Which Applies? A Guide for Doctors in England and Wales
A delirious patient refusing antibiotics or a man with psychosis walking off a medical ward: every doctor meets situations like these. This guide explains how to tell whether the Mental Capacity Act 2005 or the Mental Health Act 1983 applies, and where the law has recently changed.
Quick answer
The Mental Capacity Act 2005 (MCA) covers decisions, including any physical treatment, for people aged 16 or over who lack capacity to make a specific decision. The Mental Health Act 1983 (MHA) covers assessment and treatment of mental disorder, including detention, and capacity is not its test. The MHA cannot authorise treatment of an unrelated physical illness. If unsure, involve your senior and psychiatry early.
This guide covers England and Wales only and is not legal advice. Scotland and Northern Ireland have different laws. Always follow your trust's current policy.
What you will learn in our free Mental Health Act and Mental Capacity Act for Doctors course
Every doctor uses the Mental Capacity Act and meets the Mental Health Act — on the wards, in ED and in psychiatry. Know which law applies, and say it precisely at interview. Our free online Mental Health Act and Mental Capacity Act for Doctors course is written for NHS doctors and international medical graduates. You study at your own pace in 6 short modules, with worked examples, interactive exercises and a short quiz at the end. There is no sign-up, and your progress is saved so you can stop and come back.
The 6 modules
Foundations: two laws, two purposes: Why this matters — and what is expected of you, Two laws, two purposes, The five principles of the Mental Capacity Act
The Mental Capacity Act in practice: Assessing capacity — step by step, Recording a capacity assessment, Best interests, LPAs, deputies, advance decisions and IMCAs
Liberty, restraint and the patient who wants to leave: Restraint — when it is lawful, The patient who wants to leave, Deprivation of liberty after June 2026
The Mental Health Act: key sections: The Mental Health Act — who's who, Sections 2, 3 and 4, Holding powers: sections 5(2) and 5(4), Sections 135 and 136 — police powers, Leave, aftercare and community treatment orders
Treatment, rights and safeguards: Treatment under the Mental Health Act, Patients' rights and safeguards, Self-harm and refusal of treatment
Changes, cases and your career: What the Mental Health Act 2025 will change, Put it together — which law?, Your capacity template, CV and interviews
By the end of the course you will be able to
Explain the different purposes of the Mental Health Act 1983 and the Mental Capacity Act 2005, and choose the right one
Assess and document capacity for a specific decision using the current two-stage approach
Make best-interests decisions and use restraint lawfully and proportionately
Describe how the June 2026 Supreme Court judgment changed deprivation of liberty, and when DoLS applies
Explain sections 2, 3, 4, 5(2), 5(4), 135 and 136, leave, aftercare and CTOs — and who can use each
Describe consent-to-treatment rules, patients' rights and the role of the tribunal
Manage common situations: a patient leaving, self-harm and refusal, and a mental health crisis in ED
Summarise what the Mental Health Act 2025 will change
Why it helps your NHS application
Clear answers to everyday dilemmas: the patient who wants to leave, restraint, self-harm and refusal
Up to date with 2026: the Supreme Court's deprivation of liberty ruling and the Mental Health Act 2025
A capacity assessment template you can download and use on your next shift
How to write it on your NHS application
In your CV and on NHS Jobs or Trac: list it under "Courses and CPD" (or in the training and courses section of the form), for example:
Mental Health Act and Mental Capacity Act for Doctors, online CPD course, CareerPro UK. Certificate of completion, [month and year]; verifiable online, ID CP-XXXXXXXX.
In your supporting statement: show what you learned and how you use it. For example (adapt it so it is true for you):
"I studied the Mental Health Act and Mental Capacity Act through an online course, and I apply the two-stage capacity test and best-interests process in my clinical practice."
At interview: the course also prepares you for questions such as "A patient wants to leave the ward against medical advice. What do you do?"
Your certificate of completion
When you pass the quiz, you can download a certificate pack:
A verifiable PDF certificate of completion with your name, the course, your CPD time and a QR code that shortlisters and appraisers can scan
An appraisal-ready reflective note, pre-filled with the course learning outcomes
A ready-to-paste line for your NHS Jobs or Trac application and CV, and a one-click "Add to LinkedIn" button
Studying is free. The certificate pack is a one-off £5, and you pay only after you pass
Online course — not legal training and not approval under section 12 of the Mental Health Act.
Two laws, two different purposes
The MCA is about decisions. It applies to people aged 16 and over who cannot make a particular decision when it needs to be made, for any reason: dementia, delirium, head injury, intoxication or learning disability. It allows others to act in the person's best interests and covers almost any decision, including treatment for physical illness.
The MHA is about mental disorder. It allows a person with a mental disorder to be assessed and treated in hospital, and detained if necessary, for their own health or safety or to protect others. A person who has capacity can still be detained if the criteria are met. But the MHA only authorises treatment for the mental disorder and its direct consequences, never for an unrelated problem such as a fracture or appendicitis.
When you are unsure, ask in order:
Is the treatment for a physical problem or a mental disorder?
Does the person have capacity for this decision? If so, a decision about physical treatment stands, even if unwise.
If not, can you act in their best interests under the MCA, using the least restrictive option?
Is a mental disorder causing a risk that may need hospital assessment or treatment against their wishes? If so, involve psychiatry and consider the MHA.
The MCA: five principles and the two-stage test
Section 1 sets out five principles:
Assume a person has capacity unless it is established that they lack it.
Take all practicable steps to help them decide before concluding they cannot.
An unwise decision does not, by itself, mean a lack of capacity.
Anything done for a person who lacks capacity must be in their best interests.
Consider whether the purpose can be achieved in a less restrictive way.
Capacity is decision-specific and time-specific. Since the Supreme Court's judgment in A Local Authority v JB (2021), the test is usually approached in this order:
Functional stage: can the person understand the relevant information, retain it, use or weigh it, and communicate a decision by any means?
Causative stage: if not, is that inability because of an impairment of, or disturbance in, the functioning of the mind or brain?
A diagnosis such as dementia or schizophrenia does not, on its own, mean someone lacks capacity. Help the person decide first: choose a better time, use a professional interpreter or hearing aids, and treat pain, hypoxia or hypoglycaemia where you can.
"Lacks capacity" is not an adequate note. Record the decision, the support you gave, evidence for each ability, and how the impairment causes the inability.
Best interests, restraint and deprivation of liberty
Best interests (section 4) is not simply the medically best option, and it is not the family's decision. Consider the person's past and present wishes, feelings, beliefs and values, consult those close to them, and ask whether the decision can wait until they regain capacity. Check for a valid and applicable advance decision to refuse treatment, or a registered health and welfare lasting power of attorney covering the decision. If there is no appropriate family member or friend to consult, an Independent Mental Capacity Advocate must be instructed for serious medical treatment, except in an emergency.
Restraint (section 6) is lawful under the MCA only if you reasonably believe the person lacks capacity, that restraint is necessary to prevent harm to them, and that it is proportionate to the likelihood and seriousness of that harm. Try less restrictive options first and record what you did and why.
Deprivation of liberty changed in 2026. On 2 June 2026 the UK Supreme Court, in A Reference by the Attorney General for Northern Ireland [2026] UKSC 16, overruled the 2014 Cheshire West "acid test". Whether someone is deprived of liberty now depends on all the circumstances, including the type, duration, effects and manner of the restrictions, any objection, and their purpose. Interim Department of Health and Social Care guidance (15 June 2026) says that where there is any doubt, organisations should continue to use the Deprivation of Liberty Safeguards (DoLS) or apply to the court.
On the ward, this means:
DoLS still applies to adults aged 18 and over in hospitals and care homes. The hospital can grant itself an urgent authorisation while it applies for a standard one.
Other settings and under-18s need the Court of Protection instead.
The Liberty Protection Safeguards (LPS), legislated for in 2019, have not been brought into force, so do not describe them as current law.
Follow your trust's policy and ask your MCA lead if unsure.
MHA sections non-psychiatrists commonly meet
Section 5(2), the doctor's holding power. This allows an inpatient, including one on a medical or surgical ward, to be held for up to 72 hours while an MHA assessment is arranged. Only the doctor or approved clinician in charge of the patient's care, or their one nominated deputy, can use it, when they consider an application for detention ought to be made.
It cannot be used in the emergency department, because ED patients are not inpatients.
It is a holding power only and does not authorise treatment without consent.
Contact psychiatry straight away, give the completed statutory form to the hospital managers (usually through the MHA office), and arrange the assessment as soon as possible rather than waiting for the 72 hours to run out.
Section 5(4), the nurse's holding power. A registered mental health or learning disability nurse can hold an informal inpatient being treated for mental disorder for up to 6 hours, until a doctor who can use section 5(2) arrives.
Section 136. The police can take a person who appears to have a mental disorder and to need immediate care or control from a public place to a place of safety, for up to 24 hours, extendable by up to 12 hours in limited circumstances. If a patient arrives in ED on section 136, check their physical health first, including injuries, intoxication and overdose, and tell liaison psychiatry early.
Sections 2 and 3 at a general level
Both usually need an application by an Approved Mental Health Professional (AMHP) and two medical recommendations, one normally from a section 12 approved doctor.
Section 2 is for assessment (and treatment). It lasts up to 28 days, cannot be renewed, and is usually used when the person is not well known to services or the diagnosis is unclear.
Section 3 is for treatment when appropriate medical treatment is available. It lasts up to 6 months at first, can be renewed, and is usually used when the diagnosis and treatment are established.
For both, the person must have a mental disorder of a nature or degree warranting detention, and detention must be necessary for their health or safety or to protect others. Outside psychiatry, your role is usually to recognise the need, keep the patient safe, involve liaison psychiatry and document clearly.
The Mental Health Act 2025: what is in force
The Mental Health Act 2025 received Royal Assent on 18 December 2025 and amends the 1983 Act. Only a few limited provisions are in force: from 18 February 2026, these cover transfers of certain detained people to hospital and conditional discharge of some restricted patients. The main reforms will be brought in in phases over several years, with a new Code of Practice. They include:
stricter detention criteria based on risk of serious harm
limits on detaining people for treatment because of autism or a learning disability alone
a patient-chosen "nominated person" replacing the nearest relative
statutory care and treatment plans
ending the use of police cells as places of safety
Until each change is commenced, the 1983 Act as previously amended is the law you use.
Elsewhere in the UK, Scotland uses the Mental Health (Care and Treatment) (Scotland) Act 2003 and the Adults with Incapacity (Scotland) Act 2000, and Northern Ireland has its own legislation, including the Mental Capacity Act (Northern Ireland) 2016.
Using this at interview and in your application
"A patient wants to leave the ward against advice: what do you do?" is a common question for psychiatry, emergency medicine and medical posts. A strong answer:
Starts with safety and finds out why the patient wants to leave.
Assesses capacity for that decision.
If they have capacity, respects their choice, explains the risks, offers alternatives and safety-nets.
If they lack capacity, acts in their best interests using the least restrictive option.
If a mental disorder is driving the risk and they are an inpatient, involves psychiatry and considers section 5(2).
Escalates to a senior and documents throughout.
An anonymised reflection on a real case makes good portfolio evidence. Our guide to writing an NHS supporting statement shows how to use it, and our overview of the NHS recruitment process for international doctors explains where interviews fit.
Our free Mental Health Act and Mental Capacity Act for Doctors course works through these situations with real cases and a capacity assessment template. It is not legal training and does not lead to section 12 approval.
Start the free course
The free Mental Health Act and Mental Capacity Act for Doctors course has short modules on capacity assessment, best interests and restraint, deprivation of liberty after the 2026 Supreme Court judgment, key MHA sections, patients' rights and the Mental Health Act 2025. It is free to study, ends with a quiz, and offers an optional verifiable certificate and a reflective note for appraisal. If you would like your NHS application reviewed and rewritten (£35), email cvreviewexperts@gmail.com.
Frequently asked questions
Can the Mental Health Act be used to treat a physical illness?
No. The Mental Health Act only authorises treatment for mental disorder and its direct consequences. Treatment for an unrelated physical illness needs the patient's consent or, if they lack capacity for that decision, a best-interests decision under the Mental Capacity Act.
Can section 5(2) be used in the emergency department?
No. Section 5(2) applies only to hospital inpatients, and patients in the emergency department are not inpatients. In ED, doctors rely on the Mental Capacity Act if the patient lacks capacity, and request an urgent Mental Health Act assessment where needed.
What is the two-stage test for capacity?
First, ask whether the person can understand, retain, use or weigh the relevant information, and communicate a decision. If they cannot, ask whether that inability is because of an impairment of, or disturbance in, the functioning of the mind or brain.
Have the Liberty Protection Safeguards replaced DoLS?
No. The Liberty Protection Safeguards have not been brought into force, so the Deprivation of Liberty Safeguards still apply in hospitals and care homes in England and Wales. Since the Supreme Court's June 2026 judgment, whether someone is deprived of liberty is decided on all the circumstances.
Is the Mental Health Act 2025 in force?
Only in part. It became law in December 2025, and a few limited provisions came into force in February 2026. The main reforms will be introduced in phases, so the 1983 Act as previously amended still governs day-to-day practice.
Comments