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Distinguishing mental disorder from mental incapacity: a brief guide

Distinguishing mental disorder from mental incapacity poses a problem for clinicians. Not least because the two most relevant Parliamentary Acts are not named intuitively.

The Mental Capacity Act 2005 (MCA) provides guidance dealing only with mental incapacity, and the Mental Health Act 1983 (MHA) provides guidance only on mental disorder.

Many patients in an acute tertiary hospital suffer from a combination of both physical illness and a disturbance of their mind or their brain. In the most general terms, the MCA can give clinicians the authority to treat patients who lack capacity in their best interests. Comprehensive guidance is set out in the Mental Capacity Act 2005 code of practice.

Equally, the MHA enables clinicians to provide necessary compulsory care for a patient’s mental disorder when he or she is unable or unwilling to provide consent for that care.

It is of great importance to realise that many patients treated under the MHA retain capacity to make decisions, despite possible non-compliance with treatment for their mental disorder. The finding that a patient has a mental disorder is never by itself sufficient grounds for any compulsory measure to be taken under the MHA; the Mental Health Act 1983 code of practice chapters 14-18 sets out the circumstances when compulsion may be appropriate in an acute hospital setting:

  • Age
    The MHA is applicable to a citizen of any age. The MCA applies to citizens lacking capacity of 16 years or over; some of its provisions (of which advance decision-making is an important example for clinicians) are only applicable to adults (18 years and above). In addition, the Children Act 1989 provides parents (and others) with parental responsibility: an authority in some circumstances for adults to give consent on behalf of children (0-15) and young people (16-17) that evaporates at 18 when the person becomes an adult. But beware - parental consent may not be applicable in all situations relating to treatment under MHA (see below).
  • Threshold
    The MHA is engaged by a person’s status - that he or she is currently suffering from a mental disorder defined by the Act: ‘Any disorder or disability of mind’ and (broadly speaking, in an acute general hospital) a necessity compulsorily to care for and treat such a person’s mental disorder to protect him or others from harm when he is unable or unwilling to provide consent for this treatment.

    The MCA, by contrast, is triggered by establishing that a person lacks capacity to make a particular decision, for instance, with respect to health and welfare. The legal difficulty is that no person can give consent to treatment on behalf of an adult who lacks capacity. It is for this reason that the MCA allows treatment decisions to be made ‘in best interests’ despite the absence of consent, but taking into account evidence relating to the patient’s wishes, feelings and beliefs if known. Thus in all cases, decisions made under the MCA must be made in the patient’s best interests; if needs be, compulsion may be required to implement the decision that has been made and is authorised by the same Act.
  • Clinical application
    For healthcare decisions, the MCA in theory provides authority for the treatment of any physical or mental disorder in a patient who lacks capacity, but when compulsion is needed to provide treatment for mental disorder, the MHA in some circumstances becomes a preferable authority on which to rely. As our healthcare system has evolved, the practicalities of the division of clinical work between experts of different speciality has led increasingly to liaison psychiatrists treating mental disorder in acute hospitals such as UHS, although that distinction is by no means absolute. The MHA is inextricably linked with psychiatric training and practice in England and needs to be, since patients with a mental disorder, with or without capacity, may need to be treated on either an informal or compulsory basis under that Act. The MHA thus acts in parallel with the MCA on acute hospital wards. The choice of legal authority used being made partly on the basis of whether the patient in question has capacity, whether compulsion is required, and what illness requires treatment. 

    In some circumstances, both Acts are employed in the same patient. In a man with both dementia and diabetes, his mental disorder may be associated with longstanding behaviour from which he or others requires protection. In that case, compulsory treatment of his dementia under the MHA may be required. However, compulsory treatment for physical illness cannot be authorised by the MHA. If the patient with dementia lacks capacity, his diabetes must be treated in his best interests, and this can be provided under the authority of the MCA, together with restraint if that is proved to be necessary and proportionate to the risks he would face from non-treatment.
  • Best interests

    The principle of acting in a patient’s best interests lies at the core of the MCA; plainly, a person who has capacity (and therefore cannot fall under the MCA) makes up his or her own mind as to where their interests lie. No clinician can prescribe the interests of a person with capacity, although they can do their best to persuade, e.g. 'Do not smoke!'

    The MHA does not employ the phrase ‘best interest’ in the same way; the phrase is not indexed in the code.

  • Parental responsibility
    The MCA operates to ensure that when decisions must be made on physical treatment for an incapacitated young person, these need to be considered on the basis of his or her best interests. The parental responsibility that parents retain for this age group will usually be sufficient to allow them to consent or refuse treatment on the young person’s behalf. But in the unusual circumstances that the parents are not contactable, or appear to be in conflict with the clinicians' view of the young person’s best interests, the MCA may be engaged. 

    By contrast, the MHA has particular rules concerning the ability of those with parental responsibility to provide consent for their children. The code advises us not to rely on parental consent that overrides the refusal of a competent child or young person to an informal admission to or treatment in hospital. However, for children who are incompetent or young people who lack capacity, parental consent may be sufficient. Nevertheless, as the concept of the ‘scope of parental responsibility’ gains traction in English law, we must wait and see to what extent the decision being made falls within that scope. Please seek advice on this.
  • Depriving patients of their liberty
    Deprivation of liberty for patients with capacity and incapacity who need to be cared for under the MHA is authorised by the legal process necessary to make compulsory assessment and treatment lawful, in circumstances where the patient is unwilling or unable to provide consent. In a patient lacking capacity admitted informally for psychiatric treatment, not under the compulsion of the MHA, then if deprivation of liberty is likely, this should be authorised by the DoLS procedure. The informal patient with capacity will be free to leave, unless circumstances necessitate that compulsory detention under the MHA is arranged. 

    Many incapacitated adult patients are in an acute hospital for the purpose of receiving life sustaining treatment, under the authority of the MCA. If as a consequence of their admission they are being deprived of their liberty to allow administration of this treatment, no DoLS authorisation is necessary. However, when they reach the stage that they no longer require life sustaining treatment but still lack capacity and could be discharged, detaining them further in the hospital will require a DoLS application to make their detention lawful.

Robert Wheeler

Department of clinical law, May 2018