Mental Capacity in Prader-Willi Syndrome

The Mental Capacity Act (MCA) protects adults’ rights to make decisions.  However, in the case of people with PWS, the application of the MCA, particularly around decisions about food or the use of money, can be a challenge. 


People with PWS, if allowed to, would eat excessively and develop life-threatening levels of obesity.  They also have difficulties with impulse control and risk awareness. 


These difficulties are of biological origin and although they may have some understanding of risk, they are often unable to regulate their responses and behaviours, thereby putting their health and safety at risk. 


There have been multiple examples of people with PWS being judged to have the mental capacity to make decisions about their diet and the use of money to buy food, where they have stated that they understood the issues but have subsequently gone on to overeat and to die from the consequences.


In the case of people with PWS, focussing just on cognitive understanding will not fully address the complexity of their behaviour and any impairments in their decision-making capacity. 


It is often the context that matters and their ability to apply their understanding, weighing it up, and arriving at a decision that is a challenge. Professionals must balance all of this respecting autonomy where appropriate but also seeking to safeguard the person's wellbeing being aware of the potential serious risks to health and quality of life.


As well as dying from obesity-related complications, people with PWS can and do die from gastric rupture following a single binge eating episode, even if they do not have obesity.

Research and real world case studies have clearly evidenced that:



  • To allow someone with PWS to have free access to food and/or money that can be used to buy food is highly likely to lead to serious safeguarding risks.
  • In an environment where there is free access to food, the constant thought of food will impact their capacity to make decisions about their diet and the use of their money to buy food.
  • When access to food and money is well managed by others, adults with PWS can thrive, can have a full and meaningful life, and have a much improved life-expectancy.


The Mental Capacity Act:

Guidance for Supporting People with PWS


PWS affects decision-making, particularly regarding eating behaviour and diet.

While individuals with PWS can make decisions, their capacity may fluctuate, necessitating supervision and environmental controls.


The following recommendations are taken from "The Mental Capacity Act: Supporting People with PWS"

  • Making Decisions About Food and PWS

    Research highlights the risks associated with uncontrolled access to food for individuals with PWS, emphasizing the need for a food-managed environment to prevent significant weight gain and associated health issues.

  • Legal and Ethical Considerations

    Interventions in a person's autonomy must be justified by law, necessary, and proportionate. This aligns with Article 8 of the Human Rights Act, ensuring respect for private life while addressing the risks posed by unmanaged overeating in PWS.

  • Managing Eating Disorders in Children with PWS

    For children, parents or guardians have a duty under the Children Act (1989) to act in their best interests, including managing the eating environment. If a child is 'Gillick competent,' they may consent to aspects of their care and treatment.

  • Care and Treatment Options for Adults with PWS

    Adults with PWS need a food-managed environment. Support can be provided through:

    1. Consent to Restrictions: Adults who understand the risks and voluntarily agree to supervision or environmental controls.

    2. Mental Capacity Assessments:The MCA starts with the presumption of capacity and is decision-specific.  If an adult cannot consent due to a 'disability of the brain or mind,' the MCA allows others to make decisions in their best interests, ensuring any restrictions are necessary and proportionate.

    3.Other Legislation: The Mental Health Act is less relevant unless severe mental health issues are involved.


  • Assessing Capacity

    Capacity must be assessed for specific decisions at specific times. Individuals with PWS may need detailed capacity assessments, especially if their decision-making ability is inconsistent or if they refuse support.

  • Decision-Making Capacity

    Information on PWS, the risks of unmanaged eating, and available support should be provided to help individuals make informed decisions. Capacity assessments must distinguish between understanding information in theory (decisional capacity) and applying it in practice (executive capacity).

  • DoLs

    DoLS are legal protections put in place to keep someone safe, when they need a high level of care and supervision.

    Many people with Prader-Willi syndrome in residential settings have DoLs in place to provide the extra support they need to stay safe — for example around food, money routines, or making certain decisions.

  • Environmental Restrictions

    In PWS, restrictions to limit unsupervised eating are usually required. Such interventions must comply with Section 6 of the MCA, ensuring they are justified and necessary to prevent harm.


    For those with PWS, restrictions around food such as fridge and cupboard locks are considered to be the least restrictive option and need to remain in place to safeguard people from serious harm.


    PWS-Specific Challenges

    • High anxiety and emotional distress.
    • Impulsivity, particularly around food seeking.
    • Increased risk of harm without appropriate boundaries.
    • An intense drive to eat, putting them at serious risk.

    What good professional practice looks like:

    • Working collaboratively with health and social care teams.
    • Keeping decisions well-documented, including risk assessments and capacity assessments.
    • Seeking advice from MCA specialists or legal teams when needed.
    • Ensuring all measures are regularly reviewed to reduce restriction wherever possible.

  • Risks of Physical Restraint in PWS

    People with PWS typically present with low muscle tone, which can impact cardiovascular and respiratory function. As a result, the use of physical restraint carries a significantly increased risk of harm and has, in the past, led to serious, life-altering injuries.


    It is therefore essential that all professionals are fully aware of these risks and understand the need for alternative strategies.

Sarah Brindle, PWSA Mental Capacity Lead

Sarah Brindle: PWSA Mental Capacity Lead

Sarah is our resident expert in mental capacity, and can provide advice and support  to professionals and families caring for those with PWS.

Sarah can support you by:  

  • Attending care reviews & meetings
  • Advising on mental capacity assessments
  • Writing letters of support 
  • Advising on LPAs
  • Helping with Continuing Health Care Assessments

About Sarah

  • Sarah is a highly experienced professional with over 20 years of practice in mental capacity, health, and advocacy. 
  • Her expertise includes the Mental Capacity Act 2005, Mental Health Act 1983, associated Codes of Practice, the Human Rights Act 1998,  complex case management including serious medical treatment, DNACPRs, and advance care planning. 
  • Sarah has worked extensively in direct advocacy under IMCA, IMHA, DoLS, and Care Act frameworks, legal literacy in Court of Protection proceedings (e.g., s21A, s16, COP1–COP24) and holds the IMHA and IMCA Level 4 Qualifications.

Contact Sarah