Mental Health vs Mental Capacity

One of the first things I teach people when providing mental capacity training, is that whilst mental health and mental capacity sound the same, they are very different and don’t necessarily always co-exist. 

 Understanding the difference between the two is vital.  

What Is Mental Health? 

Mental health refers to a person’s emotional and psychological well-being. I love the explanation on the Mental Health Foundation website:

“We all have mental health, just as we all have physical health. Our mental health is how we’re feeling inside, or how we are emotionally. It’s a bit like internal weather.” 

It’s essentially how we feel and function mentally in our day-to-day lives. Good mental health helps us cope with stress, work productively, and contribute to our community. Poor mental health – as often seen in conditions like depression or anxiety – can make daily life a struggle.  

It is important that we think of mental health as existing on a spectrum: it can range from good (feeling content and able to handle life’s challenges) to bad (feeling distressed or unable to cope).  

The term “mental illness” (or “mental disorder”) is generally used when a certain set of criteria have been met (as per the Diagnostic and Statistical Manual of Mental Disorders [DSM] or the International Classification of Diseases [ICD] ) and includes disorders like depression, bipolar disorder, or schizophrenia.  

But everyone’s mental health can fluctuate over time due to stress, life events, or illness. It’s not a static label, and it’s more than just the absence of illness. 

What Is Mental Capacity? 

Mental capacity on the other hand is the ability to make decisions. In simple terms, if you have mental capacity, you can understand relevant information, remember it, weigh it up, and communicate it as part of your decision-making process. 

Mental capacity is decision specific – it’s not an all-or-nothing judgment about a person’s entire life.

A person might be capable of making some decisions but not others - this is due to something called the threshold of understanding (i.e. what a person needs to understand to make the decision). What a person needs to understand to decide what to eat for breakfast is very different to deciding where to live. 

Key Differences Between Mental Health and Mental Capacity 

Definition and Scope: 

Mental health describes our overall mental well-being and the presence or absence of mental health conditions.

Mental capacity refers specifically to the ability to make a particular decision at a particular time. Mental health is something everyone has, whereas mental capacity only becomes an issue if there’s concern someone cannot make a certain decision. 

Not Automatically Linked: 

Having a mental health problem does not automatically mean losing mental capacity.

• Many people with mental health conditions (even serious ones) can still understand information and make their own choices. Conversely, a person might lack capacity due to reasons other than mental illness – for example, a brain injury, dementia, severe learning disability, or even the effects of drugs or medication. 

  
  

• Continuum vs. Threshold: Mental health exists on a continuum from good to poor, and many people have mild or moderate mental health issues that they manage. Mental capacity, on the other hand, is more binary – for each decision, a person either has the capacity or is deemed to lack it. There is no “halfway” lacking capacity: if someone cannot meet the required threshold for a decision, the law considers them unable to make that decision. 

  
  

• Legal Treatment: There are separate legal frameworks for mental health and mental capacity. In short, mental health law is about treating illness, and capacity law is about empowering and protecting decision-makers. 

How They Can Interact  

Whilst mental health and mental capacity are different, they can influence each other. Here are a few examples to illustrate the interplay: 

• Mental Health Condition, Intact Capacity: 

 Jane has depression, she feels very low, but she still understands the choices she needs to make in life.

She can still understand, retain, weigh up and use and communicate the relevant information relating to things such as her medical treatment and the management of her finances.

Jane’s mental health is poor, but her mental capacity remains intact. Being unwell mentally doesn’t automatically equate to inability to think clearly about specific matters. 

• No Mental Illness, Diminished Capacity: 

Robert does not have a diagnosed mental health disorder, but he suffered a severe stroke that impaired his memory and understanding.

He often forgets what day it is and cannot grasp complex information. When asked to sign legal papers for selling his house, Robert cannot comprehend what the document means or remember it long enough to decide.

He lacks the mental capacity to handle this financial decision, even though he doesn’t have a “mental illness”. 

• Mental Illness Temporarily Affecting Capacity:  

Sarah has bipolar disorder. Most of the time, she manages her finances and healthcare without issues.

However, during a severe manic episode, her judgment becomes impaired – she starts spending money recklessly and cannot understand or weigh the risks and consequences of her actions. During that phase Sarah lacks capacity for capacity to manage her finances. 

However, when Sarah’s episode passes and her mental state stabilizes, her ability to understand and weigh the risks returns as does her capacity to manage her property and financial affairs. 

In Summary 

Mental health and mental capacity are related to the mind but are not the same thing. Mental health is about how we feel and function psychologically, whereas mental capacity is about the ability to make decisions.  

In all these scenarios above, the key point is that mental health and capacity must be considered separately. A person with a mental illness shouldn’t be assumed incapable of making decisions, and someone who lacks capacity isn’t necessarily mentally ill.  

The interaction is case-by-case: some mental illnesses (especially if well-managed) have little or no effect on decision-making, while some episodes or conditions can heavily impair it. 

Always look for that causative nexus – what is the impact of the mental ill-health and does it really affect the person’s ability to understand, retain, weigh and communicate the relevant information?