What the Data Actually Says About Psychoactive Substances

Let’s get one thing straight from the beginning. This is not a how‑to guide. This is not a recommendation. The use of any psychoactive substance outside of a medical context carries serious risks, and chronic or irresponsible use of any drug – including legal ones – is foolish at best and deadly at worst. You will not find me glamorising anything here.

But the data on drug harms are fascinating – and often completely misaligned with the legal status of the substances in question. A 2010 Lancet study using multi‑criteria decision analysis (MCDA) ranked 20 drugs on 16 measures of harm to both the user and society. The findings were striking: alcohol was the most harmful drug overall, with a harm score of 72 out of 100, ahead of heroin (55) and crack cocaine (54). And the same study, updated in 2016, placed alcohol as the fifth most harmful drug overall, still far ahead of many illegal substances.

The researchers considered nine harm criteria to the user and seven to others, including physical harm, dependence, economic costs, and community harm. The result is a hierarchical ladder that separates pharmacological toxicity from legal classification. Two substances stand out as having genuine medical value with comparatively low harm profiles in controlled, ethical contexts: cannabis and psilocybin. But let me be equally clear: their therapeutic potential does not justify unsupervised or illegal use. This is not a door to recreational excess – it is a call for honest, data‑driven policy and personal responsibility.

Let me walk you through the ladder.

The Overall Harm Ranking – The Data

Before we dive into each substance individually, here is a quick‑reference table based on the 2010 Nutt MCDA study (overall harm score, 0‑100):

Substance	Overall Harm Score
Alcohol	72
Heroin	55
Crack cocaine	54
Methamphetamine (crystal meth)	33
Cocaine	27
Tobacco	26
Amphetamines	23
Cannabis	20
Benzodiazepines	15
Ketamine	15
LSD	12
Psilocybin (magic mushrooms)	6
Ecstasy (MDMA)	9

Source: Nutt et al., The Lancet, 2010; additional data from various harm indices.

The Heavy Hitters – High Harm, High Risk

Alcohol

Alcohol is the undisputed heavyweight champion of drug harm. The 2010 MCDA study gave it an overall harm score of 72 out of 100 – significantly higher than heroin (55) or crack cocaine (54). Why? Because alcohol damages both the user and everyone around them. It is a leading cause of liver cirrhosis, pancreatitis, cardiomyopathy, multiple cancers, and dementia. It is involved in road traffic accidents, domestic violence, public disorder, lost workplace productivity, and family breakdown.

In 2019, alcohol consumption was associated with 2.6 million deaths globally (4.7% of all deaths) and 116 million disability‑adjusted life years (DALYs) lost (4.6% of the total). Of those deaths, an estimated 1.6 million were from non‑communicable diseases, including 474,000 from cardiovascular diseases and 401,000 from cancer. Alcohol use affected younger people than tobacco, both in terms of disability and mortality. The social harms of alcohol are enormous, and unlike many illegal drugs, alcohol is culturally embedded, widely available, and heavily marketed.

This is not an argument for prohibition – it is an observation that the legal status of a substance has little to do with its actual harm. As the study authors concluded, a new classification system that more accurately reflects drug harms is urgently needed.

Tobacco

Tobacco is the global leader in preventable deaths, causing cancer, heart disease, stroke, lung disease, diabetes, and chronic obstructive pulmonary disease (COPD). In the 2010 Nutt MCDA study, tobacco scored 26 – lower than alcohol, but still considerably more harmful than many illegal substances. Tobacco smoking causes about one in five deaths annually, and the harm is almost exclusively to the user (passive smoking aside). However, unlike many illegal drugs, tobacco has relatively low acute intoxication risk – the damage accumulates over decades.

Heroin, Crack Cocaine and Methamphetamine

These three substances are the most harmful to the individual user, scoring high on personal harm metrics. Heroin was most harmful to users, followed by crack and then methamphetamine. But overall, heroin came second and crack third, mainly because alcohol inflicted more harm on others. On a personal harm scale (0‑100), crack and heroin were rated 37 and 34, respectively, for harm to the individual, while alcohol scored lower on personal harm but far higher on social harm. The 2024 Drug Harm Index study confirmed that heroin has the highest harm index at 71.2, driven by high addiction potential, fatal toxicity, and health deterioration. Heroin is highly addictive, and long‑term use leads to profound health deterioration, infectious diseases from needle sharing, and high overdose mortality. Withdrawal is extremely unpleasant but rarely life‑threatening.

Crack cocaine is similarly addictive and destructive. Methamphetamine (crystal meth) causes severe dental problems (“meth mouth”), psychosis, violent behaviour, hyperthermia, cardiac arrest, and profound long‑term cognitive impairment. The drug is neurotoxic in ways that many other stimulants are not.

The Middle Tier – Significant Harm, Variable Risk

Cocaine (powder)

Cocaine scored 27 in the 2010 MCDA study. It is less addictive than crack but still carries high risk of cardiovascular events (heart attack, stroke, aortic dissection), nasal septal perforation, and acute psychosis. Chronic use leads to severe financial and social consequences.

Amphetamines (excluding methamphetamine)

Amphetamines (speed) scored 23. They are less potent than methamphetamine but still carry risk of psychosis, cardiac stress, and addiction. Oral use is less harmful than injection.

Benzodiazepines

Benzodiazepines (Valium, Xanax, Ativan, etc.) scored 15. They are prescribed for anxiety, insomnia, and seizures. However, they are highly addictive, and long‑term use is associated with tolerance, dependence, cognitive impairment, falls in the elderly, and severe withdrawal that can be life‑threatening. Overdose of benzodiazepines alone rarely causes death, but when combined with alcohol or opioids, the risk multiplies dramatically. Some benzodiazepines (temazepam, zopiclone, zolpidem) are more toxic than others – overdoses of these are considerably more likely to result in death than overdoses of diazepam. Paradoxically, benzodiazepines can increase the risk of suicide, anxiety, panic attacks, aggression, and violent behaviour. Withdrawal is a medical emergency.

The Low‑Harm Tier – Psychedelics and Cannabis

LSD (Lysergic Acid Diethylamide)

LSD scored 12. From a physiological perspective, LSD is known to be non‑toxic and medically safe when taken at standard dosages (50‑200μg). No deaths have been attributed to LSD’s direct effects. The primary risk is psychological – “bad trips” can lead to anxiety, panic, and in rare instances, prolonged psychotic reactions or persistent perceptual disorders (hallucinogen persisting perception disorder, HPPD). In clinical trials, adverse events such as anxiety, headache, and nausea have almost always been mild and transient. Serious adverse events, such as intense panic, suicidal ideation, and psychosis, were reported in either none or very few participants.

In uncontrolled recreational contexts, behavioural toxicity – the user failing to appreciate environmental dangers due to altered perceptions – can lead to accidents or self‑harm. However, the direct pharmacological harm is minimal.

Psilocybin (Magic Mushrooms)

Psilocybin scored 6 in the 2010 MCDA study – the lowest among all substances assessed. Psilocybin has a large therapeutic index (1:1000) and a typically unattainable lethal dose, giving it a favourable safety profile. Contemporary research has demonstrated that psilocybin is generally safe.

Emerging evidence supports its efficacy in major depressive disorder (MDD), treatment‑resistant depression (TRD), anxiety, alcohol use disorders (AUD), and cancer‑related distress. Psilocybin therapy is being studied in controlled clinical settings with promising results.

The key is control. Recreational use – especially in unsupervised settings – carries the same risks as LSD: panic, psychosis, and behavioural toxicity. But the substance itself, in pure form, is one of the least physiologically harmful drugs known. Its structure allows it to function as a serotonin receptor agonist, affecting brain wiring and leading to possible anti‑inflammatory effects. Despite initial concerns that psilocybin could cause psychosis, contemporary research has demonstrated that psilocybin is generally safe.

Cannabis

Cannabis scored 20 in the 2010 MCDA study – less harmful than alcohol (72), tobacco (26), and cocaine (27). In the 2010 ranking, cannabis placed 11th overall. A more recent Canadian comparative harm assessment published in the Journal of Psychopharmacology found that alcohol and tobacco cause significantly greater harm to individual users and society than marijuana, with alcohol receiving a cumulative weighted harm score of 79 compared to lower scores for cannabis and other substances. In that assessment, experts ranked alcohol as the substance associated with the greatest overall harm, followed by tobacco, non‑prescription opioids, cocaine, and methamphetamine.

However, cannabis is not risk‑free. Daily use of inhaled or high‑potency cannabis products is linked to elevated cardiovascular risks, including coronary heart disease, myocardial infarction, and stroke. Regular use is associated with chronic bronchitis, decreased neurocognitive function (particularly in adolescent users), cannabinoid hyperemesis syndrome (severe cyclic vomiting), psychosis (especially in those with genetic predisposition), perinatal complications, and physical injury risks (motor vehicle accidents, falls). Addiction (cannabis use disorder) affects about 9% of regular users, rising to 17% among adolescent users.

But crucially, cannabis also has established medical uses. It is used for chronic pain, spasticity in multiple sclerosis, nausea and vomiting from chemotherapy, and stimulation of appetite in HIV/AIDS. Research is exploring its role in epilepsy (CBD for Dravet and Lennox‑Gastaut syndromes), post‑traumatic stress disorder (PTSD), and other conditions.

The key distinction is method of use. Smoking cannabis is harmful to the lungs. Vaping or oral administration reduces pulmonary risk but introduces other unknowns. And as with all psychoactives, chronic or irresponsible use is ill‑advised. But compared to alcohol – which kills millions annually – cannabis is, on a population level, considerably less harmful.

Ayahuasca and Mescaline

Ayahuasca

Ayahuasca is a hallucinogenic brew made from Amazonian plants, primarily Banisteriopsis caapi (containing monoamine oxidase inhibitors, MAOIs) and Psychotria viridis (containing DMT). The DMT is orally inactive unless protected by the MAOIs. The resulting effect is a profound, hours‑long psychedelic experience.

Physiologically, ayahuasca poses real risks. Vomiting and diarrhoea are nearly universal (up to 100% of users). Nausea, headache, and abdominal pain are reported by nearly 70% of users. About 55% of users report adverse mental health effects, including hallucinations, paranoia, confusion, perceptual changes, and feeling disconnected. Cardiac complications include increased heart rate and blood pressure, and in rare cases, more serious events. Deaths have been reported, including cases of serotonin syndrome (potentially fatal) and hyponatraemia (low blood sodium, which can cause seizures and brain swelling).

Ayahuasca should never be used outside of a controlled, medically supervised setting – and even then, its safety profile is far less favourable than psilocybin or LSD. It is not a “recreational” substance by any reasonable definition.

Mescaline (Peyote)

Mescaline is a phenethylamine psychedelic found in peyote cactus and other cacti (San Pedro, Peruvian torch). Effects include hallucinations, euphoria, anxiety, increased body temperature, heart rate and blood pressure, sweating, headaches, nausea, vomiting, and impaired motor coordination.

Mescaline is regarded as relatively safe – most intoxications are mild and easily treatable. However, like all psychedelics, set and setting are critical. In traditional Native American ceremonies, the vomiting is considered a cleansing ritual. Some studies suggest potential therapeutic uses, including treatment of alcoholism and improving mental wellbeing in depression, anxiety, and substance misuse. But mescaline is not approved for any medical use, and there are no FDA‑approved medications for mescaline addiction.

Opiates and Opioids

Opiates (heroin, morphine, codeine) and synthetic opioids (fentanyl, oxycodone, methadone) are among the most addictive and lethal substances known. In the 2024 Drug Harm Index study, heroin had the highest harm index at 71.2. The 2010 Nutt MCDA study gave heroin an overall harm score of 55 (second only to alcohol). A 2024 US multi‑criteria decision analysis found that fentanyl, methamphetamine, crack, and heroin were the most harmful drugs, scoring 90, 84, 83, and 82 respectively.

Opioids cause respiratory depression, constipation, nausea, sedation, tolerance, physical dependence, and severe withdrawal. Overdose causes respiratory arrest – death from not breathing. Fentanyl is 50‑100 times more potent than morphine, and illicitly manufactured fentanyl has driven the overdose crisis. Prescription opioids (oxycodone, hydrocodone, codeine) are less harmful than street heroin when used as prescribed, but non‑medical use carries high risks of addiction, overdose, and death.

The key point: opioids have legitimate medical uses (pain relief, cough suppression, anaesthesia). But their potential for harm is immense, and chronic, irresponsible use is a direct path to disaster.

The Bottom Line

Here is the uncomfortable truth that the data make clear:

Alcohol and tobacco cause more harm than most illegal drugs – by a wide margin. Alcohol kills millions annually, destroys families, and fuels violence. Tobacco causes a fifth of all deaths. Yet both are legal, socially sanctioned, and heavily marketed.
Heroin, crack cocaine, methamphetamine, and fentanyl are the most harmful to the individual user and, in the case of heroin, to society. They are highly addictive, frequently lethal, and properly controlled. But their harm is not an argument for making alcohol or tobacco illegal – it is an argument for honest, data‑based policy.
Cannabis is considerably less harmful than alcohol, tobacco, and most illicit stimulants and opioids. It has established medical uses and a relatively low fatal toxicity. However, chronic use carries real risks, especially for adolescents, pregnant women, and those with psychiatric vulnerability. It is not “safe” – it is simply safer than many legal alternatives.
Psilocybin and LSD are among the least physiologically harmful psychoactive substances known, with exceptionally low toxicity and no established lethal dose. Their risks are primarily psychological (bad trips, panic, and, rarely, psychosis) and behavioural (accidents due to altered perception). Both have emerging therapeutic potential in controlled, supervised settings.
Ayahuasca and mescaline are less well studied, but available data suggest higher physical risks than psilocybin or LSD. Ayahuasca, in particular, carries significant medical hazards, including serotonin syndrome, cardiac complications, and death.

You have probably noticed that the old certainties are crumbling. Smoking is already on its way out – culturally marginalised, legally restricted, increasingly seen as a relic. In Finland, the official goal is a tobacco‑ and nicotine‑free nation by 2030. The National Coalition Party has proposed a generational tobacco ban to prohibit sales to anyone born in or after 2015. The minimum purchase age is being raised, taxes are climbing, and daily smoking among secondary school boys has already dropped to one percent. The message is unmistakable: a society that once tolerated smoking as normal has decided to phase it out.

Alcohol is following the same arc, though more slowly. The Finnish government raised alcohol excise duties by nearly ten percent in 2026, making heavy drinking more expensive. More importantly, the culture beneath the law is shifting. Among young adults, regular alcohol consumption has been falling for years. A 2025 European analysis found that in Finland and elsewhere, drinking among those under 35 has dropped from 72 percent two decades ago to 50 percent today. Overall alcohol sales fell by nearly three percent in 2025, with red wine dropping almost ten percent. The market itself acknowledges a “cultural pivot toward wellness, sobriety and moderation” among younger consumers. Globally, only 54 percent of Americans now drink – a ninety‑year low, and a Gallup poll found that 52 percent of adults under 35 believe moderate drinking is bad for their health, up from 34 percent a decade earlier.

These are not random fluctuations. They are the early stages of a long‑term delegitimisation. Just as tobacco moved from social essential to pariah over the course of a generation, alcohol is now beginning the same journey. The cohort‑specific policies that finished smoking – raising ages, restricting sales, steadily increasing prices – are already being discussed for alcohol.

This is also where it is worth noting, without any moral judgment, that the halal tradition has long considered alcohol and certain other substances off‑limits. What was once seen by some as a purely religious restriction is increasingly recognisable as a deeply health‑conscious stance. A person who avoids alcohol for faith‑based reasons is also, objectively, avoiding one of the most harmful psychoactive substances known – with clear benefits for liver health, heart health, cancer risk, and mental clarity. Similarly, the avoidance of pork or improperly slaughtered meat aligns with modern concerns about food safety, parasites, and processing standards. Whether you follow halal for spiritual reasons or simply because the data point the same way, the outcome is the same: a cleaner, lower‑risk lifestyle.

The aim of this post is not to encourage or normalise drug use – illegal or otherwise. The use of any psychoactive substance outside of a medical context carries serious risks. Chronic or irresponsible use of any drug is ill‑advised. The data are a tool for understanding, not a licence for experimentation. Know the numbers

The Harm Hierarchy