Intended for healthcare professionals

Head To Head Head to Head

Should the supply of cannabis be legalised now?

BMJ 2019; 366 doi: (Published 03 July 2019) Cite this as: BMJ 2019;366:l4473
  1. Molly Meacher, cross bench peer and co-chair of the All-Party Parliamentary Group for Drug Policy Reform1,
  2. David Nutt, director, Neuropsychopharmacology Unit2,
  3. Jonathan Liebling, director, Cannabis Patient Advocacy and Support Services3,
  4. Robin M Murray, professor of psychiatric research4,
  5. Adam Gridley, mental health writer and recovered cannabis user5
  1. 1House of Lords, London
  2. 2Imperial College London
  3. 3Reading
  4. 4Institute of Psychiatry, King’s College, London
  5. 5London
  1. Correspondence to: Molly Meacher meachermc{at}, R M Murray robin.murray{at}

Strict regulation would allow for healthier cannabis consumption than the criminally controlled current supply can offer, say Molly Meacher, David Nutt, and Jonathan Liebling. But Robin Murray and Adam Gridley worry that legalisation could increase cannabis use and associated psychiatric disorders

Yes—Molly Meacher, David Nutt, Jonathan Liebling

Opponents of legalisation and regulation of the supply of cannabis raise legitimate fears that it could lead to more use and therefore increased mental health harms. However, recent research in the US, where some states have legalised cannabis supply for adult social use, suggests that cannabis consumption has increased irrespective of its legal status in each state.1

Legalising and regulating cannabis confers many benefits over the current illegal and unregulated supply. Here we focus on benefits that directly affect mental and physical health.

Making consumption safer

The priority for drug policy must be to protect the mental and physical health of teenagers by discouraging cannabis use among this group and, in particular, consumption of cannabis with high concentrations of tetrahydrocannabinol (THC)—“skunk”—or contaminated products. We can expect that a proportion of teenagers who currently use skunk will access the regulated product, just as they access alcohol at present. A strong educational campaign will be important to warn of the risks associated with use. In US states with legal, regulated cannabis sales the number of teenagers taking cannabis has not risen, and in Colorado it has fallen.2

States that legalise cannabis supply can provide a safer environment for young people, but this will depend on the regulatory environment. For example, smoking cannabis with tobacco should be discouraged, and vaping of cannabis should be encouraged to reduce lung damage.

A key health issue is the composition of cannabis products. The drug may contain as many as 140 different cannabinoids in varying proportions. The two main ones are THC—often called the …

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