Summary of research findings on marijuana Review of literature ...

marijuana comes from plant cannabis sativapsychoactive ingredient is delta-9-tetrahydrocannabinol (THC)Historical Information:• hemp is made from fibre <strong>of</strong> the stem - has beenmade into rope, cloth, towels, paperInteresting fact: Until 1880, much <strong>of</strong> world’s papermade from hemp. Even today, many bank notesprinted on cannabis paper - tough and durable-evidence <strong>of</strong> hemp use (as fibre) as far back as10,000 yrs ago in China-evidence <strong>of</strong> use as intoxicant/perhaps inreligious/shamanistic practices in N-E Asia inNeolithic times (Stone Age); written records inIndia as far back as 1000 yrs ago

Interesting statistic: In both U.S. and Britain, although usagerates vary, the ratio <strong>of</strong> TLO (Tried atLeast Once) to ULM (have Used in theLast Month) to is quite similar at 4:1;in other words, it appears that only about25% <strong>of</strong> those who try marijuanacontinue to use it, and the rates <strong>of</strong>continued use vary widely from a fewtimes a year to several joints per day

• Reasons For Use:• (1977 survey <strong>of</strong> 522 British users, mainly 15-25yrs, predominantly students or recent grads) • Social uplift (pleasure, relaxation, increasedsociability) 58% • Alternative to alcohol (less harmful) 32% • Increased awareness & understanding 25% • “Simply like it” 24%

• Patterns <strong>of</strong> use (Independent DrugMonitoring Unit, Britain, 1997, survey <strong>of</strong>2469 “regular” users)• Wide range: median = 14 gm resin/month; substantial majority did notexceed this; about 5% were “heavyusers”, more or less “permanentlystoned”, > 3.5 gm/resin day

How THC worksIn ‘80s and ‘90s, experiments revealedthat THC (and its synthetic analogues)bound to unique neuron receptor siteswhich were named CB-1• The discovery <strong>of</strong> the receptors led tosearch for a naturally occurring brainchemical that bound to it• >>> discovered in the Israeli lab thathad first established that THC wasactive component <strong>of</strong> marijuana.• * Named it anandamide (after Sanskrit“ananda” = “bliss”)

Effects• • Note: subjective experience dependson dose, setting, mood (e.g., depressedvs elated), expectations, prior familiarity• alters way sensory inputs are processed andinfluences thought processes• Tends to be a euphoriant (mood enhancer)• Quickening <strong>of</strong> mental associations-- maypartially account for quickened sense <strong>of</strong>humour (p. 82)• At higher levels <strong>of</strong> intoxication (“stoned”)<strong>of</strong>ten relaxed, peaceful, reportedly pr<strong>of</strong>oundthoughts

• at very high levels, fleetinghallucinations may occur;• also, P may become introspective,dwelling on metaphysical topics >transcendental insights• appetite increases (the “stonedmunchies”!)• enhanced appreciation, enjoyment <strong>of</strong>food

Negative effects (subjective)• initial lightheadedness and dizziness,sometimes nausea, headache (morepronounced in in inexperienced users)• fear and anxiety (esp. if dose higher thannormal); can resemble panic attack• Laboratory studies: Problems in standardizingdose; and based on fact that experiencedusers can experience very different effectsthan naive Ss;• In addition: Interesting point (made in Ch. 1)that experienced users have learned to selfregulatethe high by controlling intake almoston puff-by-puff basis

• Effect on psychomotor function: neg. effect onbalance, fine motor control, reaction times (thelatter effect is relatively small)• Tests <strong>of</strong> driving impairment: early studiesshowed relatively little or no impairment; morerecent, sophisticated tests: impairment in morecomplex tasks, such as lane control;• interesting: unlike alcohol intoxication,experienced stoned drivers recognizeimpairment and usually take steps tocompensate (e.g., keep greater followingdistance)

• Findings that as many as 10% (in var.studies) <strong>of</strong> drivers involved in driving fatalitiestested positive for THC should take intoaccount that in 70-90% <strong>of</strong> these cases,alcohol also found: Problem may beinteraction effect.• Tests on pilots: tasks more complex; manyrequire divided attention; in simulators,performance consistently found to beimpaired, even 24 hours after ******• Conclusion: risks increase with taskcomplexity, lack <strong>of</strong> familiarity

Learning, Memory and other higher functions• sensory sensitivity in lab tests not heightened;reported effects presumably at perceptual level• lab tests confirm overestimation <strong>of</strong> elapsed time• Most Ss show little effect on tests requiring shorttermvigilance / attention; but performance falls <strong>of</strong>f ifconcentration required longer• Impairment is most obvious in short-term memory:dose-dependent impairment in digit-span tests,word list tests• predominant error is <strong>of</strong> “intrusion”: reportingitems that weren’t given• deficits become more pronounced if distractingstimuli presented during delay interval

• Hypothesis: Impairments in short-termmemory may underlie difficulty in maintainingcoherent train <strong>of</strong> thought - “...cannotremember where the train <strong>of</strong> thoughtbegan...” (p.94)• Acute effects on STM wear <strong>of</strong>f after 3-4hours, although some impairment may befound up to 12-24 hours.

Persistent effects <strong>of</strong> Marijuana on intellectualfunctioning?:• • recent review <strong>of</strong> literature by vanAmsterdam (1996) points outmethodological flaws in many studies(poorly matched or no control groups;testing done too soon after recent use[no washout])• Data: persistent effects from long-termuse have been reported but data areequivocal and inconsistent

• • Study (Fletcher et al. 1996) <strong>of</strong>frequent long-term users in Costa Ricafound no differences on battery <strong>of</strong>neuropsychological tests;• more recent follow-up on small group <strong>of</strong>subjects (N=17, age > 45, average use= 34 years, 5 joints per day) foundimpairment :~ 10% poorer than controls on smallproportion <strong>of</strong> the tasks (the morecomplex verbal memory tasks)

• • However: Nadia Solowij has studiedcognitive impairments in long-term users usingmore sensitive measures (ERP):• Found (1998) deficits in tests <strong>of</strong> ability toorganize and integrate complex cognitive info;• on responses to auditory stimuli requiring S to make decision and take action; one component <strong>of</strong>the ERP is delayeddeficit in selective attention ( reduced ability to rejectcomplex irrelevant stimuli)• Conclusion: There may be mild deficits inexecutive functions, but these deficitsmay not have much impact on normalday-to-day functioning.

Does marijuana use increase risk <strong>of</strong> psychosis?• [information to be added]