Addiction and Mental Health Group (AIM), Department of Psychology, University of Bath, UK.
National Addiction Centre, Institute of Psychiatry, Psychology and Neuroscience, King's College London, UK.
Addiction. 2021 May;116(5):1000-1010. doi: 10.1111/add.15253. Epub 2020 Nov 7.
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).
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.
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.
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.
高 δ-9-四氢大麻酚（THC）浓度的大麻制品会增加成瘾和精神健康障碍的风险，而大麻二酚（CBD）可能会减轻 THC 的影响。本研究旨在系统地综述和荟萃分析大麻中 THC 和 CBD 浓度随时间的变化（PROSPERO 注册：CRD42019130055）。
从 1970 年 1 月 1 日至 2019 年 3 月 27 日，通过 Embase、MEDLINE®和 Epub 提前印刷、处理中和其他非索引引文以及每日、全球健康、PsycINFO 和 Scopus 数据库，检索报告至少三个年度时间点大麻中 THC 和/或 CBD 浓度变化的观察性研究。两名独立评审员进行了搜索和提取。随机效应荟萃回归模型估计了每个研究中每种产品中 THC 和 CBD 的年度变化；这些估计值在随机效应模型中在多个研究中进行了汇总。
我们从美国、英国、荷兰、法国、丹麦、意大利和新西兰确定了 12 项符合条件的研究。对于所有草药大麻，基于八项研究中的 66747 个大麻样本（1970-2017 年），THC 浓度每年增加 0.29%（95%CI：0.11，0.47），P<0.001。对于大麻树脂，基于八项研究中的 17371 个样本（1975-2017 年），THC 浓度每年增加 0.57%（95%CI：0.10，1.03），P=0.017。草药大麻中 CBD 没有变化的证据[-0.01%（95%CI：-0.02，0.01），P=0.280；五项研究中的 49434 个样本，1995-2017 年]或大麻树脂[0.03%（95%CI：-0.11，0.18），P=0.651；六项研究中的 11382 个样本，1992-2017 年]。除了大多数研究中的非随机抽样外，偏倚风险较低。存在中度至高度异质性的证据。
1970 年至 2017 年期间，国际大麻市场上 δ-9-四氢大麻酚（THC）的浓度增加，而大麻二酚（CBD）保持稳定。大麻树脂中的 THC 增加大于草药大麻。草药大麻中 THC 的增加归因于高 THC 精麻相对于低 THC 传统草药大麻的市场份额增加。
