TY - JOUR
T1 - Changes in delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) concentrations in cannabis over time
T2 - systematic review and meta-analysis
AU - Freeman, Tom P.
AU - Craft, Sam
AU - Wilson, Jack
AU - Stylianou, Stephan
AU - ElSohly, Mahmoud
AU - Di Forti, Marta
AU - Lynskey, Michael T.
N1 - Funding Information:
No authors report any declarations of interest. This study was funded by a Senior Academic Fellowship from the Society for the Study of Addiction awarded to TF. The funder had no role in the study design, data analysis, interpretation, writing of the report or the decision to submit for publication. We thank Beau Kilmer, Fabrice Besacier, Helen Poulsen, Luca Zamengo, Sander Rigter, Pieter Oomen and Margriet van Laar for providing additional data from their studies.
Funding Information:
No authors report any declarations of interest. This study was funded by a Senior Academic Fellowship from the Society for the Study of Addiction awarded to TF. The funder had no role in the study design, data analysis, interpretation, writing of the report or the decision to submit for publication.
Publisher Copyright:
© 2020 The Authors. Addiction published by John Wiley & Sons Ltd on behalf of Society for the Study of Addiction
Copyright:
Copyright 2020 Elsevier B.V., All rights reserved.
PY - 2021/4/12
Y1 - 2021/4/12
N2 - Background and aims: Cannabis products with high delta-9-tetrahydrocannabinol (THC) concentrations carry an increased risk of addiction and mental health disorders, while it has been suggested that cannabidiol (CBD) may moderate the effects of THC. This study aimed to systematically review and meta-analyse changes in THC and CBD concentrations in cannabis over time (PROSPERO registration: CRD42019130055). Design: Embase, MEDLINE® and Epub Ahead of Print, In-Process and Other Non-Indexed Citations and Daily, Global Health, PsycINFO and Scopus were searched from inception to 27/03/2019 for observational studies reporting changes in mean THC and/or CBD concentration in cannabis over at least three annual time points. Searches and extraction were conducted by two independent reviewers. Random effects meta-regression models estimated annual changes in THC and CBD for each product within each study; these estimates were pooled across studies in random effects models. Results: We identified 12 eligible studies from the USA, UK, Netherlands, France, Denmark, Italy and New Zealand. For all herbal cannabis, THC concentrations increased by 0.29% each year (95% CI: 0.11, 0.47), P < 0.001 based on 66 747 cannabis samples from eight studies, 1970–2017. For cannabis resin, THC concentrations increased by 0.57% each year (95% CI: 0.10, 1.03), P = 0.017 based on 17 371 samples from eight studies, 1975–2017. There was no evidence for changes in CBD in herbal cannabis [−0.01% (95% CI: −0.02, 0.01), P = 0.280; 49 434 samples from five studies, 1995–2017] or cannabis resin [0.03% (95% CI: −0.11, 0.18), P = 0.651; 11 382 samples from six studies, 1992–2017]. Risk of bias was low apart from non-random sampling in most studies. There was evidence of moderate to substantial heterogeneity. Conclusions: Concentrations of delta-9-tetrahydrocannabinol (THC) in international cannabis markets increased from 1970 to 2017 while cannabidiol (CBD) remained stable. Increases in THC were greater in cannabis resin than herbal cannabis. Rising THC in herbal cannabis was attributable to an increased market share of high-THC sinsemilla relative to low-THC traditional herbal cannabis.
AB - Background and aims: Cannabis products with high delta-9-tetrahydrocannabinol (THC) concentrations carry an increased risk of addiction and mental health disorders, while it has been suggested that cannabidiol (CBD) may moderate the effects of THC. This study aimed to systematically review and meta-analyse changes in THC and CBD concentrations in cannabis over time (PROSPERO registration: CRD42019130055). Design: Embase, MEDLINE® and Epub Ahead of Print, In-Process and Other Non-Indexed Citations and Daily, Global Health, PsycINFO and Scopus were searched from inception to 27/03/2019 for observational studies reporting changes in mean THC and/or CBD concentration in cannabis over at least three annual time points. Searches and extraction were conducted by two independent reviewers. Random effects meta-regression models estimated annual changes in THC and CBD for each product within each study; these estimates were pooled across studies in random effects models. Results: We identified 12 eligible studies from the USA, UK, Netherlands, France, Denmark, Italy and New Zealand. For all herbal cannabis, THC concentrations increased by 0.29% each year (95% CI: 0.11, 0.47), P < 0.001 based on 66 747 cannabis samples from eight studies, 1970–2017. For cannabis resin, THC concentrations increased by 0.57% each year (95% CI: 0.10, 1.03), P = 0.017 based on 17 371 samples from eight studies, 1975–2017. There was no evidence for changes in CBD in herbal cannabis [−0.01% (95% CI: −0.02, 0.01), P = 0.280; 49 434 samples from five studies, 1995–2017] or cannabis resin [0.03% (95% CI: −0.11, 0.18), P = 0.651; 11 382 samples from six studies, 1992–2017]. Risk of bias was low apart from non-random sampling in most studies. There was evidence of moderate to substantial heterogeneity. Conclusions: Concentrations of delta-9-tetrahydrocannabinol (THC) in international cannabis markets increased from 1970 to 2017 while cannabidiol (CBD) remained stable. Increases in THC were greater in cannabis resin than herbal cannabis. Rising THC in herbal cannabis was attributable to an increased market share of high-THC sinsemilla relative to low-THC traditional herbal cannabis.
KW - Cannabis
KW - Cannabis resin
KW - CBD
KW - potency
KW - Sinsemilla
KW - THC
UR - http://www.scopus.com/inward/record.url?scp=85096693570&partnerID=8YFLogxK
U2 - 10.1111/add.15253
DO - 10.1111/add.15253
M3 - Review article
AN - SCOPUS:85096693570
SN - 0965-2140
VL - 116
SP - 1000
EP - 1010
JO - Addiction
JF - Addiction
IS - 5
ER -
