The dope on weed

There are good ar­gu­ments for and against al­low­ing medic­i­nal use of cannabis.

New Zealand Listener - - THIS LIFE - by Marc Wil­son

In 2016, af­ter a US con­fer­ence, I stopped off in Santa Mon­ica and stayed near Venice Beach. This fa­mous strip of Cal­i­for­nia sand is de­fined by the com­bined smells of cannabis and urine, ac­cord­ing to a re­viewer on Google Maps.

The place has a sig­nif­i­cant home­less com­mu­nity and no small num­ber of not-home­less semi-drunk uri­na­tors. There are also sev­eral “Green Doc­tors” prac­tices – green-coated peo­ple who dole out cannabis. For medic­i­nal use, of course.

Ki­wis are hav­ing a dis­cus­sion about that very ques­tion: whether and how to al­low cannabis for medic­i­nal use. One part of the de­bate might be said to be shaped by the Reefer Mad­ness stereo­type – the 1930s anti-weed pro­pa­ganda film. An­other is de­fined by ac­counts of first-hand ex­pe­ri­ence that some­times looks a lot like the film’s stereo­type. Then there are the equally poignant sto­ries of peo­ple who might be helped, per­haps dra­mat­i­cally, by eas­ier ac­cess to medic­i­nal cannabis.

So, what do we know? I did what I usu­ally ad­vise my stu­dents em­bark­ing on a re­search project to do – find the most re­cent, high-qual­ity re­view of the re­search. In this case, the first one that Google found for me was “The Health Ef­fects of Cannabis and Cannabi­noids”, a com­pre­hen­sive 2017 re­view of re­search (tak­ing into ac­count the qual­ity of that re­search) pre­pared by a com­mit­tee of the Amer­i­can Na­tional Academies of Sciences, Engi­neer­ing and Medicine. That’s a lot of words. Must be good.

Cannabis, the re­search has iden­ti­fied, con­tains more than 100 chem­i­cal con­stituents, or cannabi­noids, that act on a fam­ily of brain re­cep­tors to pro­duce the ef­fects so­ci­ety has come to know and feel am­biva­lent about. Pri­mary among cannabi­noids is tetrahy­dro­cannabi­nol, or THC, which ap­pears to be the main cul­prit for weed-in­duced in­tox­i­ca­tion. Not only are our cannabi­noid brain re­cep­tors in­volved in this process, but also things like mem­ory, mo­tor con­trol and ap­petite. Hence the munchies.

The re­searchers say there is “con­clu­sive” ev­i­dence that cannabi­noids are ef­fec­tive for treat­ing adult chronic pain, nau­sea and vom­it­ing caused by chemo­ther­apy, and lessen some of the phys­i­cal symp­toms self-re­ported by peo­ple with mul­ti­ple scle­ro­sis. There’s “sub­stan­tial” ev­i­dence for im­prov­ing sleep among peo­ple with a va­ri­ety of med­i­cal com­plaints, no­tably those in­volv­ing var­i­ous kinds of pain. On the men­tal-health front, there is “lim­ited” ev­i­dence of im­prove­ment for peo­ple ex­pe­ri­enc­ing Tourette’s, anx­i­ety, de­men­tia and post-trau­matic stress dis­or­der.

For these peo­ple, there ap­pears to be a good ar­gu­ment for tak­ing the medic­i­nal-use de­bate se­ri­ously. The re­view, how­ever, doesn’t just look at pos­i­tive out­comes.

If you’ve ever seen a US-style phar­ma­ceu­ti­cal ad­vert, you’ll know that the list of side ef­fects can be longer than the list of ben­e­fits, and the same ap­plies here. “Sub­stan­tial” ev­i­dence sup­ports con­cern over res­pi­ra­tory symp­toms among chronic users, mo­tor ve­hi­cle crash risk and lower birth­weight of off­spring. There’s also “mod­er­ate” ev­i­dence for “im­pair­ment in the cog­ni­tive do­mains of learn­ing, mem­ory, and at­ten­tion” among acute users. Or to put it an­other way – be­hav­ing like a stoner.

One of the great­est con­cerns is the sub­stan­tial ev­i­dence for de­vel­op­ment of schizophre­nia and other psy­chotic dis­or­ders. There’s also a dosere­sponse ef­fect – greater fre­quency of cannabis use tracks greater risk. For ob­vi­ous rea­sons, the re­searchers note that we have rel­a­tively fewer stud­ies look­ing at preg­nant women and ado­les­cents, but the risks are greater for both.

As a fan of ev­i­dence-based prac­tice, I’m pleased that there’s an in­creas­ing amount of ev­i­dence on cannabis ef­fects. But I don’t see this as be­ing a straight­for­ward dis­cus­sion.

There’s also “mod­er­ate” ev­i­dence for “im­pair­ment in the cog­ni­tive do­mains” – in other words, be­hav­ing like a stoner.

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