Physical & Neurological Effects
When comparing how cannabis and alcohol affect the body and brain, we are looking at the difference between a systemic cellular toxin and a targeted neuro-modulator. While both alter human consciousness, their chemical paths through our organs lead to entirely different health outcomes.
Acute Toxicity
High overdose risk. Alcohol poisoning causes fatal respiratory depression. BAC >0.40% routinely fatal.
Zero acute toxicity. No CB1 receptors in brainstem — fatal overdose is biologically impossible.
Carcinogenicity
WHO Group 1 Carcinogen (same class as asbestos). Directly damages DNA via acetaldehyde. Linked to 7 cancers.
Not classified as a carcinogen. No epidemiological link to lung cancer when controlled for tobacco.
Cardiovascular
High risk. Chronic use causes hypertension, strokes, arrhythmias, cardiomyopathy.
Low-moderate risk. Minor transient cardiovascular stress during acute use only.
Liver Damage
Severe. Causes fatty liver, alcoholic hepatitis, cirrhosis, and liver failure. 75.6% of alcohol-specific deaths.
None. Cannabinoids do not cause hepatotoxicity or liver tissue damage.
Withdrawal Safety
Life-threatening. Delirium tremens has 5% mortality rate — fatal seizures and cardiac arrest.
Physically safe. Causes insomnia, irritability, and vivid dreams but zero physical danger.
Driving Impairment
4x crash risk at 0.08% BAC. Increases risk-taking — drivers speed, cut closer, underestimate impairment.
1.2-1.3x crash risk. Drivers overestimate impairment — drive slower, leave more space, take fewer risks.
UK Driving Limits: Alcohol vs Medical Cannabis
Alcohol
As a rough guide: ~2 pints of beer (men) or ~1 pint (women) can push you to the limit. In Scotland, even a half-pint can exceed it.
Medical Cannabis
This is effectively a zero-tolerance limit. A single dose can spike blood levels past 100 μg within minutes. Regular patients will almost always exceed it.
Statutory Medical Defence
You can legally drive above 2 μg/L if: (1) the cannabis was prescribed by a specialist, (2) you take it as directed, and (3) your driving is not impaired. Carry your prescription or clinic letter at all times.
Sources: GOV.UK / CPS; Section 5A, Road Traffic Act 1988; MEDCANN Pharmacy; Drug Driving Solicitors
The Bottom Line
Alcohol is a broad-spectrum cellular toxin that systematically destroys organs, causes cancer, and rewires the brain in damaging ways. Cannabis creates functional changes that are largely reversible upon cessation. The only significant physical risk of cannabis comes from smoking it — a delivery method entirely avoidable through vaping, edibles, or oils.
Sources: Lachenmeier & Rehm (2015, Scientific Reports); Hirvonen et al. (Archives of General Psychiatry);Oxford Population Health (2024); IARC / WHO