Drug policy: where the evidence is strong, and where it is not

Drug policy is often argued as if there are only two choices: keep drugs illegal and punish people who use them, or make drugs legal. That is too simple. There are several different choices about what happens to a person caught with drugs, who is allowed to supply them, how any legal market is controlled, and how much police effort should be used against different parts of the drug market. The evidence is also uneven. We know much more about some drug treatments than we do about the effect of changing drug laws.

The clearest finding in this article is therefore not “legalise drugs” or “get tougher on drugs”. It is more basic. Treatment for dependence on heroin and similar drugs has a strong evidence base. The evidence that tougher possession laws make fewer people use drugs is much weaker. Portugal gives useful evidence about decriminalisation, but it cannot tell us what the legal change achieved on its own. Oregon is still disputed. Cannabis — commonly called weed — is a different question again.

For the police, this leads to a simple point. Arrests, drug seizures and possession offences can all be counted. They tell us what police did. They do not automatically tell us whether violence, exploitation, addiction, overdose or neighbourhood harm went down.

Start with the basics: changing what happens to a person caught with drugs is not the same as changing who is allowed to sell them.

First, what do the words mean?

Before looking at Portugal, treatment or cannabis, it helps to separate the terms that are often mixed together.

A controlled drug is simply a drug covered by the UK’s drug-control laws. Under the Misuse of Drugs Act 1971, drugs are placed into legal classes and different activities involving them can be offences.

Possession means having a controlled drug for yourself. Supply means providing it to somebody else. Supply can include selling it, but the law can also treat giving or sharing a drug as supply. The distinction matters because a policy can change the law on possession without changing the law on supply.

Prohibition or criminalisation means an activity remains against the criminal law. In the UK, possessing controlled drugs without a lawful reason is generally a criminal offence under section 5 of the Misuse of Drugs Act 1971. Producing and supplying controlled drugs are dealt with separately under the Act.

Decriminalisation usually means a person is no longer dealt with through the criminal courts for having a small amount of a drug for their own use. The drug has not necessarily become legal to make or sell. Portugal is the main example in this article: personal possession was moved out of the criminal system, while illegal supply remained a crime.

Legalisation means making something lawful that was previously unlawful. But the word is incomplete unless we say what is being legalised. A country might make possession lawful while keeping unlicensed sale illegal. Or it might also allow legal production and sale.

Full legalisation is the closest to the everyday phrase “all drugs are legal”. In its broadest form, possession, production and supply of the drugs covered by the policy would all become lawful. That still does not mean anybody could sell anything to anybody. Alcohol is legal, for example, but there are still rules about age, licensing and where it can be sold.

Legal regulation means allowing a drug legally but controlling the market. Government can decide who may make it, who may sell it, the minimum buying age, how strong products can be, packaging, advertising, price and where it can be sold. Canada’s cannabis system is an example. Cannabis is legal for adults there, but it is regulated rather than simply left to an unrestricted market.

An unrestricted or free-market model would go further and place relatively few special controls on a legal drug market. This is sometimes what people picture when they hear “legalise drugs”, but legalisation does not have to mean that.

Police diversion is different from all of these. The offence can stay in law, but an eligible person is dealt with outside the normal prosecution route. They might be sent to education, treatment or another service instead. The College of Policing explains police-led drug diversion here.

There are also a few drug names worth clearing up now. Opioids are a family of drugs that includes heroin, fentanyl and medicines such as morphine, methadone and buprenorphine. Fentanyl is an extremely powerful synthetic opioid. Diamorphine is the medical name for heroin. Naloxone is an emergency medicine that can temporarily reverse an opioid overdose. I use the familiar name first wherever possible in the rest of the article.

A Home Office paper submitted to Parliament used broadly the same distinction between prohibition, decriminalisation and different forms of legalisation. There is no perfect international dictionary, so the important thing is to describe exactly what a policy changes rather than rely on a label.

How serious is the drug problem in the UK?

Drug deaths are one useful measure of harm, but even the official figures need some explanation.

The Office for National Statistics recorded 5,565 deaths from drug poisoning in England and Wales that were registered in 2024. That was the highest number in this dataset since records began in 1993. Of those deaths, 2,621 involved an opiate or opioid — a group that includes heroin and other similar drugs. The newest arrivals in that group are nitazenes, potent synthetic opioids covered separately in Nitazenes in the UK: What Police Leaders Need to Know.

“Registered in 2024” does not necessarily mean the person died in 2024. Coroners’ investigations can take a long time. The ONS says 62.8% of the drug-poisoning deaths registered in 2024 actually happened in earlier years. The figures are therefore good for understanding the long-term problem, but less useful for saying exactly what changed during one recent year.

Scotland publishes a different set of figures. National Records of Scotland recorded 1,017 drug-misuse deaths in 2024, 13% fewer than in 2023 and the lowest number since 2017. The Scottish and England-and-Wales figures use different definitions. It would be misleading simply to add the two headline numbers together and call that a single UK total.

The law is broadly UK-wide, but the systems around it are not identical. Health services, prosecution decisions and some operational approaches differ between England and Wales, Scotland and Northern Ireland. That is why this article names the jurisdiction when it matters.

One more warning is important. A high number of deaths does not prove that prohibition caused those deaths. A fall in deaths after a law change would not prove that the law change caused the improvement either. Street drugs change, treatment changes, new drugs appear and the people using them change. Good evidence has to do more than show that two things happened at roughly the same time.

Portugal: what actually changed?

Portugal is probably the best-known example of decriminalisation, but it is often described too loosely.

In 2001 Portugal stopped treating possession of small amounts for personal use as a criminal matter. Someone caught with a personal amount could instead be dealt with through an administrative process and directed towards health or social support where needed. Selling and trafficking drugs remained criminal offences. Portugal did not make the illegal drug trade legal.

A widely cited study by Caitlin Hughes and Alex Stevens, published in the British Journal of Criminology, found that Portugal did not experience the large increase in drug use that critics had predicted. It also reported improvements in some measures of harmful drug use, health and pressure on the criminal justice system.

The difficult question is what caused those improvements. Portugal did not change only one thing. Treatment and harm-reduction services also changed. The Home Office’s 2014 international comparison therefore warned against claiming that decriminalisation alone produced the results.

So Portugal supports a modest but important conclusion: removing criminal punishment for small amounts held for personal use did not automatically lead to a large rise in drug use. It does not prove that simply changing the possession law will reduce deaths, addiction or crime in another country.

That distinction matters if England and Wales ever consider a similar change. Leaders would still have to decide what counts as a personal amount, what happens after someone is stopped, what treatment exists, what police do about public drug use, and how supply and organised crime are dealt with.

The strongest evidence is not about the law. It is about treatment

The debate about legalisation gets more attention than drug treatment. The treatment evidence is stronger.

Two medicines, methadone and buprenorphine, are commonly used to treat dependence on heroin and other opioids. They reduce withdrawal symptoms and cravings without forcing a person to keep buying unpredictable street heroin.

A 2017 BMJ review brought together 19 eligible cohorts. For people receiving methadone, the pooled all-cause death rate was 11.3 deaths for every 1,000 person-years while they were in treatment, compared with 36.1 for every 1,000 person-years while they were out of treatment. Death rates were also lower during buprenorphine treatment, although that estimate came from only three cohorts.

These were not experiments where people were randomly assigned to receive treatment or no treatment. That means other differences between periods in and out of treatment may explain part of the gap. Even with that limitation, the evidence base is strong enough that the World Health Organization strongly recommends ongoing treatment with methadone or oral buprenorphine for opioid dependence.

Then there is naloxone. Naloxone is the emergency medicine that can reverse the effects of heroin, fentanyl and other opioid overdoses when given in time. WHO recommends that people likely to witness an opioid overdose should have access to naloxone and know how to use it.

For a much smaller group, ordinary treatment does not work well enough. Some programmes provide medical heroin, called diamorphine, under close supervision. A 2023 review of randomised trials found that this approach generally kept more people in treatment and, in most studies, reduced their use of illegal street heroin compared with other opioid treatment. It is a specialist option for people with severe long-term dependence, not a general prescription of heroin to anyone who asks for it.

Dame Carol Black’s review of drug treatment in England also reached a clear practical conclusion. Her 2021 report described a treatment system that needed major rebuilding and cited an estimated return of around £4 for every £1 spent on treatment through lower costs to health services, prisons, police and other services. That £4 figure is an estimate, not a guaranteed return in every area, but it illustrates the scale of the potential benefit.

The most secure conclusion in this debate is not about whether drugs should be legal. It is that opioid-dependence treatment is associated with substantially lower mortality, and WHO strongly recommends it.

What is a drug consumption room?

A drug consumption room is a supervised place where people take drugs they already have. Staff provide clean equipment, can respond to an overdose and can connect people with treatment, housing or healthcare. The drug itself is not normally supplied by the facility.

The idea can sound shocking if it is described simply as a place where people are allowed to take illegal drugs. The purpose is more specific: reach people who are already using drugs in very dangerous circumstances and reduce some of the immediate risks.

The evidence is promising, but weaker than the evidence for methadone or buprenorphine treatment. The European Union Drugs Agency reviewed the evidence in 2026. It found signs that these facilities can reduce injecting risk behaviours, public drug use and nuisance, improve access to healthcare and possibly reduce drug deaths. But it rated the quality of evidence for these outcomes as low.

Why low? Most studies compare what happens before and after a facility opens, or compare one area with another. The facilities are usually opened in places that already have severe drug problems, making it difficult to know what would have happened without them.

Glasgow now has a real UK example. The Thistle opened on 13 January 2025. It did not make drug possession legal. Under the Lord Advocate’s prosecution policy, possession remains an offence, but prosecutors will generally not prosecute simple possession detected inside the defined facility during the pilot. That protection does not apply to drug dealing, other crimes, the surrounding area or the journey to and from the facility.

This gives Scotland an opportunity to produce better evidence. Counting how many people use the facility is useful, but it is not enough. The important questions are whether deaths, ambulance calls, public injecting, neighbourhood problems and crime change compared with what would otherwise have happened.

Oregon: a warning, but not a settled answer

Oregon in the United States is often described as proof that decriminalisation failed. The evidence is more complicated.

In 2021 Oregon stopped treating possession of small amounts of drugs as a criminal offence and planned to put money into treatment, recovery, housing and other services. Treatment capacity did not expand quickly enough to meet the state’s needs. At the same time fentanyl, an extremely powerful synthetic opioid, spread rapidly through the illegal drug supply. Overdose deaths rose sharply. Public concern grew and in 2024 Oregon brought criminal penalties for possession back, alongside new diversion routes.

The political result is clear: the policy lost public and political support. The cause of the rise in deaths is less clear.

A 2024 study in JAMA Network Open found that the apparent link between the law change and overdose deaths disappeared after researchers adjusted for the spread of fentanyl. They could not detect an increase in deaths associated with decriminalisation during the first two years.

A July 2026 working paper from the US National Bureau of Economic Research reached a different answer. Its authors used different statistical comparisons and estimated that decriminalisation was followed by a substantial increase in overdose deaths in Oregon and Washington. The paper has not yet completed the peer-review process used by academic journals, so its estimates should be weighed accordingly, but the conflicting result means the mortality question is not settled.

The fairest conclusion in August 2026 is therefore that the effect of Oregon’s decriminalisation on overdose deaths is disputed. The reform was implemented at the same time as treatment-capacity problems and a rapid fentanyl shock, and the state later reversed course. Those concurrent changes make simple before-and-after claims particularly weak.

That is a useful lesson for the UK. A law does not operate in a laboratory. Treatment has to exist in the real world. Drug markets change. Police and health services react. Public spaces matter. Copying one part of another country’s policy does not mean copying its results.

Cannabis, or weed, is a different question

Cannabis is often put into the same drug-policy debate as heroin, but the risks and policy choices are different.

One fear before legal cannabis sales began in parts of North America was that teenagers would start using much more cannabis. A 2024 JAMA Pediatrics study looking at US school survey data up to 2021 found no net increase in adolescent cannabis use associated with recreational legalisation or retail sales. Recreational legalisation was associated with modest decreases in some measures, while retail sales were associated with a lower likelihood of use but greater frequency among those who did use, producing no overall increase.

That does not mean the design of a legal market is unimportant. A 2025 Canadian study compared provinces that allowed more youth-appealing cannabis products, such as cannabis sweets and extracts, with Quebec, which had tighter rules. The researchers found higher past-year teenage cannabis use in the more permissive provinces. Because this was an observational study, it cannot prove that those product rules caused the whole difference, but it suggests that the details of regulation matter.

Legal suppliers can capture a large share of purchases, although that is not the same as proving how much illegal supply they displaced. Statistics Canada’s 2023 survey found that 71.7% of people who had used cannabis in the previous year said they bought exclusively from legal sources. That demonstrates substantial legal-market penetration. It does not mean illegal cannabis disappeared, and the survey alone does not establish the counterfactual size of the illegal market.

Strength matters too. A large study published in The Lancet Psychiatry found that daily cannabis use was associated with increased odds of a first psychotic disorder, rising to an adjusted odds ratio of 4.8 for daily use of high-potency cannabis compared with never use. Psychosis is a serious condition in which a person can lose contact with reality, for example through hallucinations or strongly held false beliefs. The study does not prove that legalising cannabis itself causes psychosis, but it supports close attention to product strength, age limits, marketing and frequency of use in any regulated market.

So the cannabis evidence does not support either extreme. Legalisation has not produced the simple explosion in teenage use that some predicted. Nor is a legal cannabis market harmless. The rules around the market matter.

What should the police take from this?

Police do not decide national drug law or run most drug-treatment services. They do decide how to use police time and what to count as success.

The College of Policing’s drug evidence briefing says the evidence for familiar tactics such as arresting suppliers and seizing drugs is limited and mixed. It suggests that enforcement is more promising when it is focused on particular places or problems and combined with problem solving.

A newer Home Office review published in 2025 looked specifically at whether drug-law enforcement reduces serious violence and homicide. Across the international studies it examined, it found limited success overall. It identified no UK-based evidence, so the international findings cannot be treated as a direct estimate of what these tactics do in the UK.

That does not mean police should stop enforcing drug laws. It means a seizure or arrest should not automatically be described as a lasting success without asking what happened next.

If police arrest a violent dealer who is exploiting children, removing that person may have an obvious purpose. If a street dealer is arrested and replaced the next day by another seller, the long-term effect is less clear. The same number — one arrest — can describe two very different outcomes.

Police diversion needs the same honesty. The College of Policing’s review of police-initiated diversion for adults rates the evidence on crime and reoffending as mixed and low quality. Its wider drug-diversion briefing describes limited but promising evidence for some drug-involved offenders. That is a reason to test diversion properly, not a reason to declare it proven.

For a police force, four practical choices follow.

Focus enforcement on harm. Give priority to violent drug markets, organised crime, exploitation of children and vulnerable adults, coercive drug debt, prison supply and places where open dealing repeatedly harms communities.

Do not confuse activity with results. Arrests, warrants, searches and seizures are useful information. Add measures that ask whether violence, exploitation, repeat offending and neighbourhood harm actually fell.

If people are diverted, find out what happens next. Record whether they reach the service, complete it, return to police attention or reoffend. A referral is not an outcome.

Make police contact a route into effective treatment where possible. Custody, overdose incidents and other repeated contacts put police in front of people at high risk. Local systems should make it easier for those people to reach or stay in treatment and obtain naloxone.

The simplest way to read the evidence

There is no single scientific answer called “the correct drug policy”. Different policies change different things.

We can be fairly confident that methadone and buprenorphine treatment are associated with substantially lower mortality among people dependent on heroin and other opioids, and WHO strongly recommends these treatments. Naloxone can reverse an opioid overdose when administered in time. Medical heroin has a smaller specialist role for some people who have not responded to ordinary treatment.

We can be reasonably confident that Portugal did not experience the predicted explosion in drug use after decriminalising personal possession, but we cannot separate that law change neatly from improvements in treatment and support.

We have weaker evidence on drug consumption rooms, even though the results so far are promising. We have genuinely disputed evidence from Oregon. And cannabis regulation has to be judged on its own rules, including age, strength, products, marketing and price.

For the public and for policing, the useful question is therefore not simply whether a policy sounds tough or liberal. It is much simpler: what exactly is being changed, what problem is it meant to solve, and did that problem actually get smaller?

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Sources and further reading

• Office for National Statistics, Deaths related to drug poisoning in England and Wales: 2024 registrations.
• National Records of Scotland, Drug-related deaths in Scotland, 2024.
• Misuse of Drugs Act 1971 and section 5: possession.
• Home Office memorandum to Parliament, Drug policy terminology and options.
• Home Office, Drugs: international comparators, 2014.
• Home Office, The impact of drug-related law enforcement activity on serious violence and homicide: a systematic review, 2025.
• Hughes, C. E. and Stevens, A., What Can We Learn From The Portuguese Decriminalization of Illicit Drugs?, British Journal of Criminology, 2010.
• Sordo, L. et al., Mortality risk during and after opioid substitution treatment, BMJ, 2017.
• World Health Organization, updated recommendations on opioid dependence treatment, 2026, and opioid overdose guidance.
• McNair, R., Monaghan, M. and Montgomery, P., Heroin assisted treatment for key health outcomes in people with chronic heroin addictions, Drug and Alcohol Dependence, 2023.
• Dame Carol Black, Review of drugs part two: prevention, treatment, and recovery, 2021. Applies to England.
• European Union Drugs Agency, Health and social responses: drug consumption rooms, updated June 2026.
• Crown Office and Procurator Fiscal Service, Drug consumption room statement of prosecution policy, 2025.
• Zoorob, M. J. et al., Drug Decriminalization, Fentanyl, and Fatal Overdoses in Oregon, JAMA Network Open, 2024.
• Hall, D., Hansen, B. and Matsuzawa, K., Did Drug Decriminalization Increase Overdoses?, NBER Working Paper 35427, 2026.
• Coley, R. L. et al., Recreational Cannabis Legalization, Retail Sales, and Adolescent Substance Use Through 2021, JAMA Pediatrics, 2024.
• Mital, S. and Nguyen, H. V., Legalizing Youth-Friendly Cannabis Edibles and Extracts and Adolescent Cannabis Use, JAMA Network Open, 2025.
• Statistics Canada, National Cannabis Survey, 2023.
• Di Forti, M. et al., The contribution of cannabis use to variation in the incidence of psychotic disorder across Europe, The Lancet Psychiatry, 2019.
• College of Policing, Drug crimes evidence briefing: key findings, police-led diversion, and Police-initiated diversion for adults.