What is an addiction?

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Page last updated Monday 29th Jun 2026
Page written by Victoria McCann at Castle Craig, Scotland

Searching for the definition of an addiction is almost always for a deep and personal reason. Perhaps you’re feeling an invisible pull towards something you’d rather avoid, or you’ve been watching someone close to you change, and the question doesn’t go away.

Knowing is half the battle, so getting a better understanding of the way addictions form and operate can help us in overcoming them.

We’re broadly exploring the premise of what addiction is, what causes it, the many forms it takes and how it’s treated. Addiction has multi-faceted and powerful drivers that lead to confusion and despair, so let this page serve as your starting point. We hope to guide you towards positive change, and a healthier, brighter future.

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The definition of addiction

Addiction is a recognised medical condition that changes how the brain processes reward, motivation, and self-control. It leads to compulsive use of a substance, or compulsive engagement in a behaviour, even when it’s clearly causing harm. The NHS defines addiction as not having control over doing, taking, or using something to the point where it could be harmful to you.

It is classed as a chronic, relapsing condition. It can return after periods of recovery, and it tends to need ongoing management rather than a one-off fix. It’s not a moral failing, and it’s not the same as a casual habit, or even a very strong preference for something.

in a corridor, a therapist is explaining to her patient what an addiction is
What addiction isn't

So what does addiction actually mean? The word gets used loosely. People say they are addicted to coffee, to their phone, to a TV series, and most of the time, nobody means it clinically. While we might all be guilty of using the word, overly casual use can make the clinical condition harder to recognise, when it shows up.

According to peer-reviewed neuroscience research, the brain’s reward circuit becomes less able to respond to non-drug rewards. Compulsive use follows, and continues despite serious harm, even when the person genuinely wants to stop.

Clinical addiction stands separately from a habit or preference. It involves changes to how the brain works, and we can broadly say that willpower isn’t the lever. Addiction is a health condition that responds to treatment, in the same way other chronic conditions do. It is not something a person can simply decide their way out of.

What causes addiction?

There is no single cause, and that itself is part of what makes addiction difficult to source, even among experts. Start with the brain.

The American National Institute on Drug Abuse describes the difference between a normal reward and a drug-driven reward as the difference between someone whispering and someone shouting through a microphone. Drugs and addictive behaviours produce surges of dopamine far larger than anything from everyday life. Over time, the brain adjusts by producing less dopamine on its own, or by reducing the number of receptors that can pick it up. Everyday pleasures can start to feel flat, and a person ends up needing more of the substance or behaviour to get the same effect.

Man with implied bipolar disorder and addiction looking wistfully out of a window

Brain chemistry is only part of the picture. According to the same body of peer-reviewed research, addiction develops in people who are vulnerable because of a combination of genetics and developmental or adverse social exposures. Mental health, environment, and earlier life experience all play a part. 

We can broadly surmise that no single factor explains addiction on its own, and research into drivers of addiction continues to paint a complex and fascinating picture.

I’m 5 years sober now and I know I wouldn’t have survived another month before I joined the treatment programme. Castle Craig is an amazingly special place where miracles really do happen, I’m blessed to have found you.

Jackie

What are the different types of addiction?

Addiction takes many forms, and the form matters. Some involve a substance, where the body and brain adapt to the presence of alcohol, a drug, or a medication. Others are behavioural, where the same reward pathways are activated by an activity rather than a chemical.

The core mechanism is shared. What differs is how the addiction shows up day to day, and what the right treatment approach looks like. For that reason, more clinicians and experts in addiction distinguish between substance and behavioural addictions.

Below are listed some of the most common behaviours and drugs found in recovery:

a man with a concerned family behind him showing signs of heroin addiction
Substance addictions

Substance addictions involve compulsive use of a chemical that changes how the brain and body function. The most common forms we treat include:

Behavioural addictions

Behavioural addictions activate the same reward pathways as substances, without a chemical being taken into the body. They are sometimes harder to recognise for that reason, both in yourself and in someone in your life. The most common forms include:

Signs you or someone in your life may have an addiction

The signs of addiction are better understood as potential patterns, rather than as a checklist. We can also broadly say that they show up gradually. They involve a loss of control over use, and continued use even when the harm becomes visible.

Common signs include:

  • Using more, or for longer, than intended
  • Finding it difficult to cut down or stop, even when wanting to
  • Spending more time and money on the substance or behaviour
  • Secrecy around the extent of use
  • Physical or emotional withdrawal symptoms when stopping
  • Continuing despite clear harm to health, work, finances, or relationships
  • Losing interest in things that previously mattered
a family benefiting from a family support programme provided by their therapist
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How addiction is treated

Addiction is treatable, and treatment usually involves a combination of medical and therapeutic support. The right approach depends on both the form of addiction and the broad scope of a person’s physical and mental health.

For most people, treatment begins with a clinical assessment and, where needed, a medically assisted detox. From there, the work moves into therapy, group support, and longer-term aftercare. Recovery is not often a single event. We plan for it as a process, with continuing care after the inpatient stage, because that is what the evidence supports.

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Addiction and Mental Health

Addiction also frequently overlaps with other mental health conditions, and the two can feed into each other. We have a separate page on how addiction and mental health often appear together.

More on dual-diagnosis
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Frequently asked questions about addiction

Is addiction classed as a mental health condition?

Yes. Addiction is recognised as a mental health condition, and it is one of the most common to appear alongside others. The clinical term for that overlap is dual diagnosis, and it changes how treatment is planned.

Can you become addicted to something that isn’t a drug?

Yes. Behavioural addictions activate the same reward pathways in the brain as substance addictions, even though no chemical is taken into the body. Gambling, gaming, pornography, sex, shopping, and compulsive use of certain online platforms are all recognised forms. The clinical mechanism is similar between substance-related and non-substance-related addictions.

How long does it take to develop an addiction?

There’s no fixed timeline, and it varies between people and substances. Opioids and some stimulants can produce dependence within weeks. Others build over months or years, and behavioural addictions often develop slowly enough that the start is hard to pin down. Genetics, mental health, and circumstances all affect how quickly it takes hold.

Is addiction hereditary?

Partly. Family history of addiction raises risk, but it isn’t deterministic. Plenty of people with a family history never develop an addiction, and plenty without one do. Genetics shapes the ground that environment and experience build on.

What’s the difference between dependence and addiction?

Dependence describes the body’s physical adaptation to a substance, so that stopping produces withdrawal. Addiction is broader. It includes a loss of control and continued use despite clear harm. Someone can be physically dependent on a prescribed medication without being addicted. And someone can be addicted to a behaviour that produces no physical dependence at all.

Can someone recover from an addiction without professional support?

Some people do. But the evidence is clear that recovery rates are significantly higher with structured treatment, particularly for moderate to severe addiction. Professional support also reduces the risk of relapse, addresses any co-occurring mental health conditions, and provides the medical oversight that detox sometimes requires. Recovery without support is possible. Recovery with support is more likely, and usually more sustainable.