{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,30]],"date-time":"2026-10-30T00:53:47Z","timestamp":1793321627439,"version":"4.5.0"},"reference-count":59,"publisher":"Wiley","issue":"5","license":[{"start":{"date-parts":[[2020,11,7]],"date-time":"2020-11-07T00:00:00Z","timestamp":1604707200000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/creativecommons.org\/licenses\/by-nc\/4.0\/"}],"content-domain":{"domain":["onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["Addiction"],"published-print":{"date-parts":[[2021,5]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:sec>\n                    <jats:title>Background and aims<\/jats:title>\n                    <jats:p>Cannabis products with high delta\u20109\u2010tetrahydrocannabinol (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\u2010analyse changes in THC and CBD concentrations in cannabis over time (PROSPERO registration: CRD42019130055).<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Design<\/jats:title>\n                    <jats:p>Embase, MEDLINE\u00ae and Epub Ahead of Print, In\u2010Process and Other Non\u2010Indexed 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\u2010regression models estimated annual changes in THC and CBD for each product within each study; these estimates were pooled across studies in random effects models.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>\n                      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),\n                      <jats:italic>P<\/jats:italic>\n                      \u00a0&lt;\u00a00.001 based on 66\u2009747 cannabis samples from eight studies, 1970\u20132017. For cannabis resin, THC concentrations increased by 0.57% each year (95% CI: 0.10, 1.03),\n                      <jats:italic>P<\/jats:italic>\n                      \u00a0=\u00a00.017 based on 17\u2009371 samples from eight studies, 1975\u20132017. There was no evidence for changes in CBD in herbal cannabis [\u22120.01% (95% CI: \u22120.02, 0.01),\n                      <jats:italic>P<\/jats:italic>\n                      \u00a0=\u00a00.280; 49\u2009434 samples from five studies, 1995\u20132017] or cannabis resin [0.03% (95% CI: \u22120.11, 0.18),\n                      <jats:italic>P<\/jats:italic>\n                      \u00a0=\u00a00.651; 11\u2009382 samples from six studies, 1992\u20132017]. Risk of bias was low apart from non\u2010random sampling in most studies. There was evidence of moderate to substantial heterogeneity.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusions<\/jats:title>\n                    <jats:p>Concentrations of delta\u20109\u2010tetrahydrocannabinol (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\u2010THC sinsemilla relative to low\u2010THC traditional herbal cannabis.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.1111\/add.15253","type":"journal-article","created":{"date-parts":[[2020,11,7]],"date-time":"2020-11-07T19:01:10Z","timestamp":1604775670000},"page":"1000-1010","update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":249,"title":["Changes in delta\u20109\u2010tetrahydrocannabinol (THC) and cannabidiol (CBD) concentrations in cannabis over time: systematic review and meta\u2010analysis"],"prefix":"10.1111","volume":"116","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-5667-507X","authenticated-orcid":false,"given":"Tom P.","family":"Freeman","sequence":"first","affiliation":[{"name":"Addiction and Mental Health Group (AIM), Department of Psychology University of Bath  UK"},{"name":"National Addiction Centre, Institute of Psychiatry, Psychology and Neuroscience King's College London  UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5663-2731","authenticated-orcid":false,"given":"Sam","family":"Craft","sequence":"additional","affiliation":[{"name":"Addiction and Mental Health Group (AIM), Department of Psychology University of Bath  UK"},{"name":"National Addiction Centre, Institute of Psychiatry, Psychology and Neuroscience King's College London  UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jack","family":"Wilson","sequence":"additional","affiliation":[{"name":"The Matilda Centre for Research in Mental Health and Substance Use The University of Sydney  Australia"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Stephan","family":"Stylianou","sequence":"additional","affiliation":[{"name":"National Addiction Centre, Institute of Psychiatry, Psychology and Neuroscience King's College London  UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Mahmoud","family":"ElSohly","sequence":"additional","affiliation":[{"name":"National Center for Natural Products Research, School of Pharmacy University of Mississippi  USA"},{"name":"Department Pharmaceutics and Drug Delivery, School of Pharmacy University of Mississippi  USA"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Marta","family":"Di Forti","sequence":"additional","affiliation":[{"name":"Social, Genetic and Developmental Psychiatry Centre King's College London  UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9989-737X","authenticated-orcid":false,"given":"Michael T.","family":"Lynskey","sequence":"additional","affiliation":[{"name":"National Addiction Centre, Institute of Psychiatry, Psychology and Neuroscience King's College London  UK"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2020,11,7]]},"reference":[{"key":"e_1_2_8_2_1","doi-asserted-by":"publisher","DOI":"10.1038\/nrn.2016.28"},{"key":"e_1_2_8_3_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.pharmthera.2018.10.006"},{"key":"e_1_2_8_4_1","doi-asserted-by":"publisher","DOI":"10.1111\/bph.13250"},{"key":"e_1_2_8_5_1","doi-asserted-by":"publisher","DOI":"10.1038\/sj.bjp.0704327"},{"key":"e_1_2_8_6_1","doi-asserted-by":"publisher","DOI":"10.1038\/sj.bjp.0707442"},{"key":"e_1_2_8_7_1","doi-asserted-by":"publisher","DOI":"10.1007\/s00213-002-1169-0"},{"key":"e_1_2_8_8_1","doi-asserted-by":"publisher","DOI":"10.1038\/sj.npp.1300496"},{"key":"e_1_2_8_9_1","doi-asserted-by":"publisher","DOI":"10.1111\/add.12634"},{"key":"e_1_2_8_10_1","doi-asserted-by":"publisher","DOI":"10.1111\/add.12508"},{"key":"e_1_2_8_11_1","doi-asserted-by":"publisher","DOI":"10.1017\/S0033291715001178"},{"key":"e_1_2_8_12_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.drugalcdep.2017.06.015"},{"key":"e_1_2_8_13_1","first-page":"1","article-title":"Characterising heterogeneity in the use of different cannabis products: latent class analysis with 55 000 people who use cannabis and associations with severity of cannabis dependence","author":"Craft S.","year":"2019","journal-title":"Psychol Med"},{"key":"e_1_2_8_14_1","doi-asserted-by":"publisher","DOI":"10.1001\/jamapsychiatry.2020.1035"},{"key":"e_1_2_8_15_1","doi-asserted-by":"publisher","DOI":"10.1016\/S2215-0366(14)00117-5"},{"key":"e_1_2_8_16_1","doi-asserted-by":"publisher","DOI":"10.1016\/S2215-0366(19)30048-3"},{"key":"e_1_2_8_17_1","doi-asserted-by":"publisher","DOI":"10.1016\/S2215-0366(16)30188-2"},{"key":"e_1_2_8_18_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.drugalcdep.2018.11.012"},{"key":"e_1_2_8_19_1","first-page":"1","article-title":"Changes in cannabis potency and first\u2010time admissions to drug treatment: a 16\u2010year study in the Netherlands","author":"Freeman T. 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