Letter is actually talking about Spice not weed !
Re: Cannabis consumption by UK teens is a ticking time bomb, warns president elect
I concur with all the points made by Shubulade Smith, based in part on the whole spectrum of psychotic illness observed over decades by Robin Murray. Particularly for some adolescent males, cannabis use precipitates psychosis – not all users, not in all groups, but in a way that relates to an early onset of use, frequency of use, and THC content. Synthetic cannabinoids can give the biggest and most consistent hit  and the devastating impact of designer “Spice” on socially excluded young people gives me special concern for Public Health.
 Caan W. Deeply designed drugs. European Journal of Neuroscience 1991;3 Suppl 4: 322.
Competing interests: Early in my career, I published research on psychoses related to substance use, e.g. Mathers DC, Ghodse AH, Caan AW, Scott SA. Cannabis use in a large sample of acute psychiatric admissions. British Journal of Addiction 1991; 86: 779-784.