Nýlegar rannsóknir mínar hafa sýnt að munur önnur en notkun kannabis gæti verið að valda mikill-rætt misræmi í vitræna starfsemi
Hvort eða ekki nota kannabis getur leitt til vitglapa er heitt umræðuefni rannsókna og almannahagsmuna. í ljósi þess að Miklar athygli fjölmiðla veitt niðurstöðum sem benda skaðleg áhrif kannabis á skilvitlegri, heilastarfsemi og andleg heilsa, þú vildi vera fyrirgefið fyrir að hugsa reykja spliff var í ætt við ítrekað roknahögg sjálfur yfir höfði með risastór Bong. Hins, þar sem mikið af vinnu til þessa er kross-sectional (sem er, mælingar eru gerðar aðeins á einu í lífi einstaklingsins), we cannot know whether cannabis users would have performed any differently before they started using cannabis. Í stuttu máli, we’re faced with a classic “chicken or egg” problem.
Cannabis use does not occur in a vacuum. And teenagers who start using cannabis from a young age will almost certainly differ from those who will never try, it or who delay until they are older. The evidence suggests that those who start using cannabis from a young age often have less stable backgrounds og more behavioural problems than their non-using peers. Teenage cannabis use also typically goes hand in hand with other drug use and risky lifestyle choices in general. The poorer cognitive performance of cannabis users may therefore result from other factors associated with cannabis use, rather than cannabis use itself. Hins vegar er það að sjálfsögðu mjög erfitt að stjórna öllum þessum annarra þátta.
Að reyna að takast á þessum málum, ásamt öðrum vísindamönnum frá University College London og University of Bristol (þ.mt Suzi Gage sem hýsir þetta blogg), Ég hef tekið þátt í nýrri rannsókn, með hugsanlega óvart niðurstöður. Nota gögn um 2235 Unglingar safnað sem hluta af "Börn 90" árgangi frá Suður-Vestur Englandi, Við leit á sambandið á milli hversu oft einhver tilkynnt hafa notað kannabis eftir aldri 15, og árangur þeirra á IQ próf lokið á sama aldri. Vert unglingar höfðu einnig tekið IQ próf þegar þeir voru 8 ára (áður en einhver þeirra höfðu notað kannabis), svo við gætum takast á "kjúklingur eða egg" vandamál.
Í fyrstu lítur Niðurstöður okkar til kynna að þeir unglingar sem notuðu kannabis flutt verri á unglingsárunum prófunum IQ þeirra, eftir grein fyrir þeirra "grunngildi" IQ á 8 ára. Jafnvel þeir sem höfðu aðeins notað kannabis handfylli af sinnum skoraði u.þ.b. 2 IQ stigum lægri en þeir sem höfðu aldrei prófað hass. Hins, Við benti einnig á að unglingar sem notuðu kannabis voru miklu líklegri til að hafa notað sígarettur, áfengi og önnur fíkniefni- og allir þessir þættir einnig spáð lægri táninga IQ skorar. Flestir sláandi við sáum að kannabis notendur voru einnig mun líklegri til að vera tóbak sígarettu reykja- 84% þeirra sem eru í þyngsta kannabis hópnum okkar (sem tilkynnt hafa notað kannabis að minnsta kosti 50 sinnum eftir aldri 15) hafði reykt sígarettur meira en 20 sinnum í lífi sínu, samanborið við bara 5% of those who had never used cannabis.
When we statistically adjusted for these differences in rates of other substance use, along with other factors including childhood behavioural problems and mental health symptoms, cannabis use no longer predicted lower IQ scores. After this adjustment even our heaviest group of cannabis users had predicted IQ scores no different to those who had never tried cannabis. We also ran a similar analysis to look at the same teenager’s school GCSE grades, which they sat at age 15/16. The findings were similar to our IQ findings- while cannabis users achieved lower grades at GCSE (the equivalent of 2 grades lower on one subject), once we took account of these other related factors cannabis use no longer predicted worse school performance.
It seems therefore that there is something else about these two groups of teenagers (those who had used cannabis by age 15 and those who had not) that is responsible for the differences in IQ and school grades, rather than their cannabis use, though it’s not clear what from our study. Although cigarette smoking was identified as a potentially important factor, we clearly can’t know from this type of study whether it actually causes lower IQ and school performance, and there is little evidence elsewhere to suggest this is the case.
While this may sound like great news for those 15% af 15-24 year old Europeans who have used cannabis in the past year, the take home message is sadly not so clear cut. This is just one study from one cohort in one area of England, and as authors of the paper we are the first to acknowledge the limitations of this work, including the young age of the participants when we measured IQ, and the relatively moderate levels of cannabis use.
A well-publicised study from 2012 suggested that cannabis use starting in adolescence and persisting into mid-life “is” related to IQ decline. So how do these potentially opposing findings fit together? The key difference between að 2012 rannsókn and ours is the type of cannabis users included in the study. Our heaviest using teenagers had been using cannabis for approximately 2 ár, and had used cannabis at least 50 times each (þó 57% of this group reported having used cannabis at least 100 sinnum). Í 2012 study those who showed the most dramatic IQ decline had been persistent cannabis users from adolescence until their late 30’s, and had been diagnosed with cannabis addiction at numerous points in their life. So it’s possible that cannabis addiction, rather than cannabis use per se, is related to lower IQ, or that persistent heavy cannabis use throughout your lifetime can to have these negative effects.
Our study is by no means definitive, but it does highlight that we should all be more cautious when jumping to conclusions about the harms of a drug before we have strong evidence either way. Overly forceful conclusions about the potential negative effects of cannabis are unscientific and based on an incomplete evidence base. This can lead to the unfair marginalisation of teenagers who use cannabis, which is the last thing we would want, given that this group is likely to include some of the most vulnerable in society.
Claire Mokrysz is a PhD student at University College London investigating whether teenagers are particularly susceptible to harm from cannabis and alcohol use.
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