Long-term effects of cannabis
[1] In 2017, the U.S. National Academies of Sciences, Engineering, and Medicine issued a report summarizing much of the published literature on health effects of cannabis, into categories regarded as conclusive, substantial, moderate, limited and of no or insufficient evidence to support an association with a particular outcome.
[9] Cannabis dependence develops in 9% of users, significantly less than that of heroin, cocaine, alcohol, and prescribed anxiolytics,[10] but slightly higher than that for psilocybin, mescaline, or LSD.
[11] A 2018 academic review, published in partnership with Canopy Growth, discussed the limitations of current studies of therapeutic and non-therapeutic cannabis use, and further stated that the nature of dependence formation among regular marijuana consumers has declined since 2002.
[13] Acute cannabis intoxication has been shown to negatively affect attention, psychomotor task ability, and short-term memory.
[16][17] Chronic use of cannabis during adolescence, a time when the brain is still developing, is correlated in the long term with lower IQ and cognitive deficits.
The authors concluded that: Cannabis intoxication was not only found to affect attention, psychomotor task ability, and short-term memory.
[25] According to the National Academies of Sciences, Engineering and Medicine, there is substantial evidence of a statistical association between cannabis use and the development of schizophrenia or other chronic psychoses, with the highest risk potentially among the most frequent users.
[26] Medical evidence strongly suggests that the long-term use of cannabis by people who begin use at an early age display a higher tendency towards mental health problems and other physical and development disorders, although a causal link could not be proven by the available data.
[26] Another review that same year concluded that cannabis use may cause permanent psychological disorders in some users such as cognitive impairment, anxiety, paranoia, and increased risks of psychosis.
[33] An opposing view was expressed by Suzanne Gage and coauthors reviewing the literature available in 2016, who regarded the epidemiologic evidence on cannabis use and psychosis strong enough "to warrant a public health message that cannabis use can increase the risk of psychotic disorders," but also cautioning that additional studies are needed to determine the size of the effect.
[37] For some locations, this translates into a substantial population attributable risk, such that "assuming causality, if high-potency cannabis types were no longer available, then 12% of cases of first-episode psychosis could be prevented across Europe, rising to 30% in London and 50% in Amsterdam.
Even in those with no family history of psychosis, the administration of pure THC in clinical settings has been demonstrated to elicit transient psychotic symptoms.
Chronic users who use for anxiolytic purposes will even develop dependencies on cannabis, making it difficult to cope with anxiety when the drug is absent.
A recent study assessing changes in neuropsychological functioning resulting from long-term cannabis use followed a group of adolescents (ages 12 –15 at baseline) over a 14-year period.
It is important to know that studies looking at associations between cannabis use and poor neurocognitive functioning have found that extended abstinence from marijuana leads to improvements in cognitive deficits.
A February 2019 systematic review and meta-analysis found that cannabis consumption during adolescence was associated with an increased risk of developing depression and suicidal behavior later in life, while finding no effect on anxiety.
[58] This is common in cannabis users when they hit a point of their high that could lead to paranoia, anxiety, increased heart rate.
The authors cautioned that "evidence is needed, and further research should be considered, to prove causal associations of marijuana with many physical health conditions".
[71][72] Long term cannabis users are at risk for developing cannabinoid hyperemesis syndrome (CHS), characterized by recurrent bouts of intense vomiting.
[3] A 2013 review which specifically examined the effects of cannabis on the lung concluded "[f]indings from a limited number of well-designed epidemiological studies do not suggest an increased risk for the development of either lung or upper airway cancer from light or moderate use, although evidence is mixed concerning possible carcinogenic risks of heavy, long-term use.
They concluded that "[o]ur pooled results showed no significant association between the intensity, duration, or cumulative consumption of cannabis smoke and the risk of lung cancer overall or in never smokers."
They cautioned that "[o]ur results cannot preclude the possibility that cannabis may exhibit an association with lung cancer risk at extremely high dosage."
The same authors supported further study, and called attention to evolving means of cannabis consumption: "Specifically, respiratory risks may differ with the use of water pipes and vaporizers or with consuming oral preparations.
[79] Smoking cannabis has been linked to adverse respiratory effects including: chronic coughing, wheezing, sputum production, and acute bronchitis.
In a few case reports involving immunocompromised patients, pulmonary infections such as aspergillosis have been attributed to smoking cannabis contaminated with fungi.
Isoprenes help to modulate and slow down reaction rates, contributing to the significantly differing qualities of partial combustion products from various sources.
[91] A study released by the National Academies of Sciences, Engineering, and Medicine cited significant evidence for a statistical link between mothers who smoke cannabis during pregnancy and lower birth weights of their babies.
[93] A report prepared for the Australian National Council on Drugs concluded cannabis and other cannabinoids are contraindicated in pregnancy as it may interact with the endocannabinoid system.
[62] Due to the small number of studies that have been conducted, the evidence is insufficient to show a long-term elevated risk of mortality from any cause.
Motor vehicle accidents, suicide, and possible respiratory and brain cancers are all of interest to many researchers, but no studies have been able to show a consistent increase in mortality from these causes.
