Many of us hear the word “drug” and immediately associate it with something only available by illegal means. Yet some of the most addictive drugs aren’t illegal at all. We can buy some of them in a pharmacy or a supermarket, or we can get them with a doctor’s prescription.
With so many drugs available legally, it’s hard to know which ones carry greater risks of addiction, or even which category they fall into. We are giving support for you or someone you know to make safer decisions, even when the drug itself is legal.
What are legal drugs?
Legal drugs are substances that can be bought, prescribed, or consumed without breaking the law. In the UK, this covers a wider range of substances than most people realise. Alcohol, nicotine, prescription painkillers, anti-anxiety medications, sleep aids, and certain stimulant medications are all, by this definition, legal drugs.
The word ‘legal’ describes how a substance is classified and regulated. It says nothing about how safe it is, or whether it can cause dependence.
Why some legal drugs can be addictive
We become dependent on a substance when repeated use changes the way our brain functions. The brain adapts to the presence of the drug over time, reducing its natural response, so that more is needed to achieve the same effect. This is called tolerance. When the substance is then reduced or stopped, the brain takes time to readjust, producing withdrawal symptoms that can range from mild discomfort to serious medical problems.
Legal status doesn’t change biological responses to a drug. According to guidance published in the British Journal of General Practice, benzodiazepines should only be prescribed at the lowest effective dose for a maximum of two to four weeks This is specifically because physical dependence can develop quickly, even at mild doses.
For people taking prescribed medications, dependence can develop even when a drug is taken exactly as directed. NHS England data shows that over one million people in England were prescribed opioids continuously for more than three months, as of January 2021. Developing a dependence on a prescribed medication is not unusual. It’s one of the most common routes into treatment that we see at Castle Health.
The three categories of legal drugs in the UK
Legal drugs in the UK fall into three distinct groups. Each carries a different addiction profile and a different route to dependence. Becoming dependent on a prescribed opioid is quite different from developing dependence with alcohol, even if the underlying drivers share common ground.
Prescription medications
Some of the most widely prescribed drugs in the UK carry a genuine risk of physical dependence. They were developed to treat real conditions, but extended use is a different matter.
According to a 2019 report from Public Health England (now the Office for Health Improvement and Disparities), 11.5 million adults in England, 26% of the adult population, received at least one prescription for opioids, benzodiazepines, gabapentinoids, antidepressants, or ‘Z’ drugs in 2017/18. Of those, 5.6 million people (13% of the adult population) were prescribed an opioid pain medicine.
The key prescription drugs in this category include:
- Opioids (codeine, tramadol, oxycodone, morphine): opioids bind to receptors in the brain and nervous system to reduce pain. With continued use, the brain adapts and tolerance develops. Understanding how opioid dependence develops can help anyone taking pain-relieving medications long-term.
- Benzodiazepines (diazepam, lorazepam, temazepam): prescribed for severe anxiety, panic disorder, and insomnia, these drugs enhance the effect of GABA (gamma-aminobutyric acid), a brain chemical that slows the nervous system. Becoming dependent on benzodiazepines carries serious withdrawal risks including seizures, and typically requires a medically supervised reduction.
- ADHD stimulants (methylphenidate, lisdexamfetamine): used to treat ADHD, these medications increase dopamine and noradrenaline activity. Extended use without oversight can produce tolerance, and stopping suddenly may cause significant lows in mood and energy.
- Sleep medications – ‘Z’ drugs (zolpidem, zopiclone): like benzodiazepines, these act on the GABA system. With regular use, natural sleep becomes harder to achieve without them. Stopping can trigger rebound insomnia, sometimes more severe than the original sleep difficulty.
Legally available substances – alcohol, nicotine, and codeine products
Some of the highest dependence-forming drugs in the UK require no prescription. They’re sold freely and rarely described as drugs, but pharmacologically, that’s what they are.
Alcohol
Alcohol is embedded in British social life in a way that obscures its risk for dependence. According to the Office for National Statistics, there were over 10,000 deaths from alcohol-specific causes in the UK in 2023. Estimates from the Office for Health Improvement and Disparities place the number of alcohol-dependent adults in England at around 608,000 as of 2019/20. Both figures paint a bleak picture of alcohol’s wide-reaching effects across the country.
Alcohol produces dependence through its effects on GABA receptors and glutamate activity in the brain. With regular heavy drinking, brain chemistry adjusts to compensate. When drinking is reduced or stopped, that adjustment reverses, producing withdrawal symptoms that range from anxiety and tremors to, in severe cases, seizures or delirium tremens (DT). Alcohol withdrawal is medically serious and requires clinical supervision.
If you’re concerned about alcohol addiction, learning about specialist treatment is often the best first-step.
Nicotine
Nicotine is among the most rapidly addictive substances known. Research published in Tobacco Control found that the first symptoms of dependence can develop within days of starting to smoke. Almost two-thirds of people studied reported at least one symptom of nicotine dependence, often before they were smoking daily.
NHS Stop Smoking Services data from Q3 2025/26 recorded 187,923 quit attempts in that period alone. Of those who set a quit date and successfully stopped, 11.8% had their results confirmed by carbon monoxide testing. The scale of uptake shows how seriously clinical services treat nicotine dependence.
Codeine-containing products
Some over-the-counter medicines contain codeine, an opioid. Co-codamol is the most common example, but certain cough syrups also qualify. Used short-term at recommended doses, the dependence risk is low. Regular use over time triggers the same tolerance and withdrawal processes as prescription opioids. Because these products sit on pharmacy shelves, we might not even associate them with dependence, yet their addictive properties can be serious.
Synthetic legal highs and new psychoactive substances
The phrase ‘legal high’ is misleading and, in the UK, now largely inaccurate. Substances previously sold under that label were developed to mimic the effects of controlled drugs while technically avoiding legal classification. But the Psychoactive Substances Act 2016 made the supply of most of these substances illegal in the UK.
What continues to develop is a constant stream of new synthetic substances. The European Union Drugs Agency (EUDA) reported that 50 new psychoactive substances were identified for the first time in 2025, and approximately 400 previously reported substances were detected on the market in 2024. At the end of 2025, EUDA was monitoring 1,050 new psychoactive substances in total.
Their unpredictability is what makes them dangerous. What they’re made from can vary between batches, and the effects, which can include acute psychosis and cardiovascular crisis, are often more intense than the substances they mimic. Since 2009, 95 new opioids have been identified on the European drug market. Seven were notified in 2025 alone, including nitazene and orphine compounds that can be hundreds of times more potent than heroin.
‘I contacted Castle Health seeking guidance and options to support a relative who was having a difficult time both with addiction and other mental health concerns. The team were incredibly kind and informed, they took the time to go through all the options with me and helped us plan how to approach the matter. Fortunately, the person has now been receiving care from Castle Health for several months and is doing really well. A big thank you to the wonderful team. I would highly recommend this service.’
When to seek help with legal drug dependence
There’s no threshold you need to reach before it makes sense to ask for support. Many people wait because the substance was prescribed, or because they’re not sure what they’re experiencing counts. Both are worth questioning.
Signs that dependence may be developing
- Needing more of the substance to get the same effect as before
- Symptoms returning between doses: anxiety, pain, or low mood
- Finding it harder to reduce or stop than expected
- Taking a medication outside the prescribed dose or schedule
- Not being entirely honest with your GP about how much you’re taking
- Drinking every day, or feeling unsettled when you cannot
- Someone in your life has raised a concern about your use
Seeking support is appropriate at any stage, including when the substance was prescribed, and including when you aren’t certain whether what you’re experiencing is serious enough.
How to get help with addiction to legal drugs
If you’re concerned about your use of a prescribed medication, your GP is a good first step. They can review your prescription and discuss a supervised reduction. Being honest and specific about dosage and duration means you’ll be given the safest option.
For people who have tried to reduce without success, or whose dependence has developed to a point where more specialist support is needed, treatment options for prescription drug dependence are available. Castle Health provides residential treatment through Castle Craig in Scotland and Smarmore Castle in Ireland, as well as outpatient services for those who need clinical support but cannot commit to a residential stay.
Medical detox means that withdrawal is managed under clinical supervision, at a pace and with medications that reduce any risk. Knowing what opioid withdrawal involves can help break down the barrier to asking for help.
Talk to our team
If you’re concerned about dependence on a legal drug, prescribed or not, our clinical team is here to help. There’s no obligation and no minimum threshold before getting in touch.
