Marijuana
Cannabis is an illicit substance commonly used recreationally as the psychoactive drug marijuana.
Below are some of the health effects of marijuana use.
http://m.pnas.org/content/113/5/E500.abstract
(2015) Jackson et. al., show that, "Marijuana users had lower test scores relative to nonusers and showed a significant decline in crystallized intelligence between preadolescence and late adolescence," and further show that twins did have IQ declines, but they were less stark than other more broadly-grouped results purported.
http://www.pnas.org/content/109/40/E2657.abstract
(2012) Meier et. al., show that, "Persistent cannabis use was associated with neuropsychological decline broadly across domains of functioning, even after controlling for years of education. Informants also reported noticing more cognitive problems for persistent cannabis users. Impairment was concentrated among adolescent-onset cannabis users, with more persistent use associated with greater decline."
They also state that, "Further, cessation of cannabis use did not fully restore neuropsychological functioning among adolescent-onset cannabis users. Findings are suggestive of a neurotoxic effect of cannabis on the adolescent brain."
http://jop.sagepub.com/content/early/2016/01/06/0269881115622241.abstract
(2016) Mokrysz et. al., analyze IQ and educational outcomes in teenagers in relation to their cannabis use.
They show that IQ loss due to smoking cannabis is slightly attenuated by cigarette use and other negative habits and that cognitive impacts in non-weighted (non-g) measures of IQ may be less than previously found. Their tests did not account for loss to memory.
https://www.ncbi.nlm.nih.gov/pubmed/23836598
(2014) Hall & Degenhardt discuss the adverse health effects of chronic cannabis use.
They reveal that, "These most probable adverse effects of regular use include a dependence syndrome, impaired respiratory function, cardiovascular disease, adverse effects on adolescent psychosocial development and mental health, and residual cognitive impairment."
https://www.ncbi.nlm.nih.gov/m/pubmed/12901774/
(2003) Grant et. al., analyze the non-acute or residual neurocognitive effects of cannabis use.
There was little effect on IQ in six of the eight cognitive domains they analyzed, but two domains - learning and forgetting - that is, memory and understanding - were significantly impaired.
https://www.researchgate.net/profile/Jean_Lud_Cadet/publication/11039020_Dose-Related_Neurocognitive_Effects_of_Marijuana_Abuse/links/559964c808ae793d138050d7.pdf
(2002) Bolla et. al., analyze the dose-related neurocognitive effects of marijuana abuse.
In their own words, "Very heavy use of marijuana is associated with persistent decrements in neurocognitive performance even after 28 days of abstinence. It is unclear if these decrements will resolve with continued abstinence or become progressively worse with continued heavy marijuana use."
All groups using marijuana showed cognitive declines and higher doses were associated with greater declines.
http://cannabis.free.fr/medias/cannabis_et_QI.pdf
(2002) Fried et. al., analyze the spatial domains of IQ in order to ascertain marijuana's effects on them.
In their own words, "Current marijuana use was significantly correlated (p < 0.05) in a doserelated
fashion with a decline in IQ over the ages studied."
Abstinence from the drug brought back most function, but it is important to note that they did not analyze memory or attention which show significant continuous deficits in other studies.
https://sci-hub.ac/10.1016/0376-8716(91)90072-7
(1991) Nakamura et. al., analyze the effects of relatively light THC use on memory in the rat.
Their analysis reveals significant declines on working memory as a result of THC administration. Chronic effects on this section of memory were largely reversed after prolonged abstinence.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4428682/
(2014) Pedersen et. al., analyze how expectancies play into symptoms of marijuana use.
Their analysis reveals that strong positive expectancies and weak negative expectancies usually led to greater marijuana use. Both groups saw depression, anxiety, and other mental health aberrations occur.
http://pubmedcentralcanada.ca/articlerender.cgi?accid=PMC2797098
(2007) Budney et. al., show that marijuana can cause dependency. That is, contrary to non-expert opinions on marijuana and the THC and CBD compounds, they are in-fact addictive.
They analyze many problems associated with use, as well.
https://jamanetwork.com/journals/jamapsychiatry/fullarticle/481834
(2001) Pope, Gruber & Hudson analyze the neuropsychological performance of long-term cannabis users.
Their analysis shows that, "At days 0, 1, and 7, current heavy users scored significantly below control subjects on recall of word lists, and this deficit was associated with users' urinary 11-nor-9-carboxy-Δ9-tetrahydrocannabinol concentrations at study entry."
Non-memory IQ domains seemed to recover after abstinence from use of the drug.
http://europepmc.org/abstract/med/1313532
(1992) Nahas & Latour investigate the human toxicity of marijuana.
In their own words, "Marijuana smoke is mutagenic in the Ames test and in tissue culture and cannabinoids inhibit biosynthesis of macromolecules. In animals, marijuana or delta 9-tetrahydrocannabinol (THC), the intoxicating material it contains, produces symptoms of neurobehavioural toxicity, disrupts all phases of gonadal or reproductive function, and is fetotoxic."
They go on to say that, " Clinical manifestations of pathophysiology due to marijuana smoking are now being reported. These include: long-term impairment of memory in adolescents; prolonged impairment of psychomotor performance; a sixfold increase in the incidence of schizophrenia; cancer of mouth, jaw, tongue and lung in 19-30 year olds; fetotoxicity; and non-lymphoblastic leukemia in children of marijuana-smoking mothers."
Marijuana and its metabolites are toxic to the brain, reproductive systems, liver, and the lungs at least. (Larson et. al., 2008) confirms the presence of neurotoxic metabolites from THC.
https://www.ncbi.nlm.nih.gov/pubmed/19630708
(2008) Solowij & Battisti analyze the chronic effects of cannabis on memory in humans. They state, " the evidence suggests impaired encoding, storage, manipulation and retrieval mechanisms in long-term [of] heavy cannabis users."
https://www.ncbi.nlm.nih.gov/pubmed/24483000
(2013) Sagie et. al., analyze the short-and long-term effects of cannabinoids on memory, cognition and mental illness.
They find a number of adverse cognitive and physical effects of marijuana use including an elevation of schizophrenia symptoms.
They state that the positive uses of marijauna are, "reducing pain, anxiety and nausea, increasing appetite and an anti-inflammatory activity." They then warn that medicalization of marijuana increases use which increases depression as a result of use of the drug.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3930618/
(2015) Jacobus & Tapert analyze the effects of cannabis on the adolescent brain. Their analysis shows current research does show negative cognitive and developmental side-effects of marijuana use. They recommend greater and more rigorous research.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3931635/
(2013) Schoeler & Bhattacharyya analyze the effect of cannabis use on memory function.
They conclude that, "[...] evidence regarding the acute impairments in memory function induced by cannabis is generally robust, particularly for those using cannabis with a lower proportion of CBD and higher proportion of Δ9-THC. In other words, the effects are likely to depend on the type of cannabis used (ie, the greater the dose of Δ9-THC, the greater the memory impairment)."
They likewise state that youth marijuana use could see adverse developmental side-effects.
https://www.ncbi.nlm.nih.gov/pubmed/19837255
(2009) Hall & Degenhardt analyze the adverse health effects of non-medical cannabis use.
They show a variety of psychosocial and physical side-effects arise from use.
https://pdfs.semanticscholar.org/85ee/204cd4a55b90d92dcd844538f0784067af82.pdf
(2016) Sullivan analyzes the cellular and molecular mechanisms underlying learning and memory impairments produced by cannabinoids.
He shows that cannabinoids have a variety of effects on parts of the brain. They alter hippocampal responsiveness, they're found at high density in the hippocampus and tend to compete there, they inhibit hippocampal long-term potentiation and long-term depression of synaptic transmission, they decrease release of acetylcholine and GABA from the hippocampus, they decrease glutamate release, they reduce neurotransmitter release, they inhibit the activation of pre-synaptic calcium channels, their receptor ligands reduce learning and memory on their own, and many more austere effects.
(Hall, Degenhardt & Teesson, 2004; Parolaro, 2010; Vadhan, Serper & Haney, 2009; Hall & Degenhardt, 2008; D'Souza, Sewell & Ranganathan, 2009; Shrivastava et. al., 2014; Radhakrishnan, 2014; and many more) all confirm that THC and CBD are related to the development of mental illnesses, especially schizophrenia, and the revelation of them in susceptible individuals and populations.