Are We Criminalizing Biology? Half of London’s Detainees May Have Undiagnosed ADHD

A startling new study reveals that up to 50% of suspects may have undiagnosed ADHD.

A startling new study from the UK raises an uncomfortable question: if a suspect’s brain works differently, is the justice system punishing their intent or their biology?

Research led by the University of Cambridge suggests that one in two individuals arrested and detained in London may have undiagnosed attention-deficit/hyperactivity disorder (ADHD). Furthermore, up to one in 10 may have undiagnosed autism.

If 50% of detainees are struggling with a condition that affects impulse control and decision-making, simply locking them up might not just be unfair — it might be ineffective.

Screening Suspects

The study, led by Dr. Tanya Procyshyn of Cambridge’s Autism Research Centre and Senior Detective Dion Brown, took a snapshot of life in six London custody centers over eight weeks in 2024. The team offered voluntary screenings for neurodivergence to 303 detainees.

The uptake was surprisingly high — 71% agreed to be screened. This suggests that the people in these cells are often looking for answers about their own minds.

The results were stark. While autism affects about 3% of the general adult population, nearly 10% of the detainees either had a diagnosis or screened positive for likely undiagnosed autism.

But the real kicker came for ADHD. Around 8% of the arrested subjects had an ADHD diagnosis. This is slightly higher than the 5% prevalence in the usual population. But an additional 1 in 2 people scored at or above the threshold for possible undiagnosed ADHD. Of them, 17% had a very high number of ADHD traits.

“Screening for ADHD and autism at the first point of contact with law enforcement benefits both the criminal justice system and the individuals involved,” says Dion Brown, a senior Detective from the Metropolitan Police Service.

The Self-Medication Trap

Perhaps the most telling finding relates to why these individuals were arrested in the first place. The researchers found a strong link between neurodivergence and drug offenses.

Six in ten individuals arrested for drug-related crimes had either a diagnosis or a positive screening result for ADHD. This makes physiological sense: ADHD is fundamentally a disorder of dopamine regulation, the brain’s reward and pleasure chemical. People with untreated ADHD often suffer from chronically low levels of dopamine, leading to a restless search for stimulation.

In this context, illegal substances can become a crude, dangerous form of self-medication.

By arresting these individuals without screening them, the system often creates a revolving door. We confiscate the drugs they use to cope, lock them in a cell that exacerbates their symptoms, and release them without addressing the underlying physiological deficit.

“To ensure fair treatment in the criminal justice system, we need to understand how neurodivergence affects interactions with the law. This can help avoid unnecessary criminalisation of misunderstood behaviour and ensure that potentially vulnerable individuals are able to access appropriate support,” says Dr. Tanya Procyshyn a research associate at the Autism Research Centre at the University of Cambridge.

Preventing Crime

This research argues for a pivot from punishment to diversion. If a crime is driven by a treatable medical condition, treating the condition protects the public far better than a prison sentence does.

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But this isn’t about letting people off the hook.

“Early identification helps officers interpret behaviours that might otherwise be misunderstood and ensures appropriate support is provided. This approach creates opportunities to divert vulnerable individuals away from the criminal justice process and towards the help they may need.”

Currently, the justice system assumes a ‘standard’ brain when determining intent and culpability. This study suggests that, at least in London holding cells, that assumption is biologically flawed. If we want a system that is truly fair, we have to start looking at who we are arresting — and why.

Journal Reference: Brown, D & Procyshyn, TL et al. Neurodiversity in custody: Screening results for ADHD and autistic traits in individuals arrested by the London Metropolitan Police. Criminal Behaviour and Mental Health; 10 Dec 2025; 10.1002/cbm.70018