How Bad Is Marijuana for Your Health?

May 3, 2014

The Jour­nal of Neu­ro­science recently pub­lished a study link­ing recre­ational mar­i­juana use to sub­tle changes in brain struc­ture. The researchers, led by Jodi Gilman of Mass­a­chu­setts Gen­eral Hos­pi­tal, iden­ti­fied increased gray mat­ter den­sity in the left nucleus accum­bens and some bor­der­ing areas. The study was fine, but the media cov­er­age was abysmal. Reporters over­stated the find­ings, mis­char­ac­ter­ized the study, and failed to men­tion pre­vi­ous research done on pot smok­ing and health. Gold­fish may not have a three-second mem­ory, but some jour­nal­ists seem to. When a new paper comes out, it’s often treated as the first ever and final word on the topic. There is a sig­nif­i­cant body of lit­er­a­ture on the neu­ro­log­i­cal and wider health effects of mar­i­juana, and to ignore it when cov­er­ing new stud­ies seems to me a form of jour­nal­is­tic mal­prac­tice. A press release from the Soci­ety for Neu­ro­science trum­peted the Gilman study’s impor­tance because it looked at casual users rather than reg­u­lar pot smok­ers, who form the basis of most mar­i­juana stud­ies. That claim is dubi­ous in the extreme. The sub­jects aver­aged 3.83 days of smok­ing and 11.2 total joints per week. Char­ac­ter­iz­ing these peo­ple as casual pot smok­ers was a great media hook, but it defied com­mon sense. Occa­sional users won­dered if they’d done per­ma­nent dam­age, and par­ents were con­cerned that their teenagers might face pro­found neu­ro­log­i­cal changes from exper­i­ment­ing with pot. Any reporter who read the study, how­ever, should have known not to take that bait. Even by the stan­dards of past med­ical stud­ies, it’s a stretch to call these sub­jects casual pot smok­ers. Just two years ago, for exam­ple, Janna Cousijn and col­leagues pub­lished a study on a group that she called “heavy” mar­i­juana users. In the aver­age week, they smoked 3 grams of cannabis—approximately 2 grams less than Gilman’s casual smok­ers. (A joint has about 0.5 grams of cannabis.) The jus­ti­fi­ca­tion for call­ing Gilman’s sub­jects casual smok­ers is that they didn’t meet the cri­te­ria for depen­dence, but when you count up the joints, the study doesn’t look so rev­o­lu­tion­ary. Many sto­ries also claimed that the Gilman study showed direct cau­sa­tion between pot smok­ing and brain abnor­mal­i­ties. That’s wrong. The study looked at dif­fer­ences between pot smok­ers and abstain­ers at a sin­gle moment. Only a lon­gi­tu­di­nal study, exam­in­ing brain changes over time, could have sug­gested cau­sa­tion. As a let­ter writer to the Jour­nal of Neu­ro­science noted, it’s pos­si­ble that pre-existing brain dif­fer­ences cause some peo­ple to seek out mar­i­juana. Gilman’s pot smok­ers also drank more and smoked more cig­a­rettes than the con­trol group, which sup­ports this inter­pre­ta­tion and also raises the pos­si­bil­ity that other fac­tors led to brain struc­ture dif­fer­ences. The biggest prob­lem with the cov­er­age of the mar­i­juana study was that it failed to put the new research into con­text. Valentina Loren­zetti of the Uni­ver­sity of Mel­bourne recently pub­lished a widely cited review paper syn­the­siz­ing dozens of stud­ies on mar­i­juana and the brain. Tak­ing the lit­er­a­ture as a whole, there is evi­dence sug­gest­ing that mar­i­juana use causes struc­tural changes in three parts of the brain: the frontal lobes, tem­po­ral lobes, and the cere­bel­lum. The data also rein­forces the idea that long-term, heavy smok­ers expe­ri­ence greater changes than casual users. The stud­ies, how­ever, have seri­ous flaws. They are typ­i­cally small and have been unable to show that the struc­tural changes cause cog­ni­tive impair­ment. Gilman’s study of 20 smok­ers is a good con­tri­bu­tion to the lit­er­a­ture, but it doesn’t resolve those prob­lems. If you are con­sid­er­ing smok­ing pot—or quitting—here is what you need to know. Smok­ing mar­i­juana once is very unlikely to harm you. It takes at least 15 grams of cannabis to kill a per­son, and prob­a­bly much more than that. A healthy per­son would have to smoke dozens of joints in a sin­gle ses­sion to risk death from over­dose. Peo­ple who do die from the acute effects of mar­i­juana die in acci­dents: A recent study sug­gested that more than 10 per­cent of dri­vers killed in car acci­dents test pos­i­tive for cannabis.* The more likely risk from try­ing mar­i­juana is depen­dence. There is a debate over whether mar­i­juana is addic­tive, but you needn’t bother with it—it’s mainly about seman­tics. The fact is, approx­i­mately 9 per­cent of peo­ple who start smok­ing pot become depen­dent by ordi­nary med­ical stan­dards. That’s low com­pared with depen­dence rates for other drugs: More than 15 per­cent of peo­ple who drink become alco­holics, and 32 per­cent of peo­ple who try cig­a­rettes get hooked. Still, you should think seri­ously about a 1-in-11 chance of addic­tion, espe­cially if you have a per­sonal or fam­ily his­tory of sub­stance abuse. What sorts of health risks are these reg­u­lar cannabis users tak­ing? It’s extremely chal­leng­ing to study the long-term health effects of mar­i­juana in humans. You can’t legally ask 1,000 peo­ple to smoke three joints a week for 40 years just to see what hap­pens, so researchers can only com­pare health data from peo­ple who admit to smok­ing pot with data from peo­ple who don’t admit to it. Ret­ro­spec­tive cor­re­la­tional stud­ies like these raise all kinds of prob­lems, such as match­ing the groups for con­found­ing vari­ables. (Do they smoke cig­a­rettes? Do they have a fam­ily his­tory of can­cer? What do they eat? Do they exer­cise?) Even if you assume that every­one is telling the truth, there are also bound to be wide vari­a­tions in how much pot the sub­jects used. Most stud­ies sug­gest that any poten­tial health risks of cannabis are dose-dependent—people who smoke only a lit­tle face very few health risks, while peo­ple who smoke a lot are more likely to get sick—but this is still largely a mat­ter of con­jec­ture. With that caveat out of the way, here are some find­ings. Stud­ies con­sis­tently show that fre­quent mar­i­juana smok­ing is asso­ci­ated with some forms of res­pi­ra­tory dys­func­tion. Smok­ers report prob­lems with cough­ing, wheez­ing, and phlegm. Lung can­cer is a murkier issue. Cannabis smoke con­tains higher con­cen­tra­tions of some car­cino­gens than cig­a­rette smoke does. Some large stud­ies show increased preva­lence of res­pi­ra­tory tract can­cers in cannabis users, while oth­ers find no cor­re­la­tion. With the legal­iza­tion of recre­ational mar­i­juana in some states, many peo­ple have asked whether they can min­i­mize can­cer risk by ingest­ing rather than smok­ing cannabis. It’s a rea­son­able sug­ges­tion. At this point, how­ever, the ques­tion is unan­swer­able. There sim­ply aren’t enough peo­ple with a long his­tory of eat­ing mar­i­juana, but not smok­ing it, to put together a study. Inges­tion may be risky, because it seems eas­ier to overindulge in food prod­ucts than in smok­ing. Col­orado is cur­rently review­ing its reg­u­la­tions after acci­den­tal deaths involv­ing ingested cannabis. Keep­ing cannabis brown­ies is espe­cially risky if you ever have chil­dren in your home. A study released last year sug­gested that an increas­ing num­ber of chil­dren in Col­orado are acci­den­tally eat­ing marijuana-laced food prod­ucts. The cog­ni­tive effects of chronic mar­i­juana use are uncer­tain. If you’re an adult who smokes occa­sion­ally, there appears to be lit­tle or no rea­son to believe your men­tal per­for­mance will suf­fer. Sev­eral stud­ies also show that those who expe­ri­ence impair­ments may recover if they stop smok­ing. Heavy, long-term smok­ers may expe­ri­ence mem­ory and atten­tion loss. There is also some indi­ca­tion that heavy mar­i­juana users are more likely to be diag­nosed with schiz­o­phre­nia, but it’s not clear which is the cause and which the effect, if indeed there is such a rela­tion­ship; it may be the case that peo­ple with schiz­o­phre­nia are self-medicating with mar­i­juana. As with alco­hol and tobacco, it’s fairly clear that minors should not use mar­i­juana. Many stud­ies show that kids who smoke pot do poorly in school, and some stud­ies sug­gest that they com­mit sui­cide at higher rates. Although the causal rela­tion­ship isn’t clear, the risks are too great. You prob­a­bly have plenty of other ques­tions. For exam­ple, is mar­i­juana less bad for you than alco­hol or tobacco? The com­par­i­son is basi­cally impos­si­ble to make. Moun­tains of data link cig­a­rette smok­ing to a stag­ger­ing col­lec­tion of adverse events. It’s dif­fi­cult to know whether the same goes for mar­i­juana, because fewer peo­ple smoke it, and those who do typ­i­cally smoke less pot than cig­a­rette smok­ers do tobacco. Com­par­ing alco­hol with marijuana—aside from dif­fer­ences in acute tox­i­c­ity and dri­ving competence—is also imprac­ti­cal. Seri­ously, though, if you’re try­ing to decide among smok­ing pot, tak­ing up cig­a­rettes, and drink­ing alco­hol based on health risks, I sug­gest find­ing a dif­fer­ent hobby. *Cor­rec­tion, May 1, 2014: Due to an edit­ing error, this piece mis­stated that almost 25 per­cent of dri­vers killed in car acci­dents test pos­i­tive for cannabis. Almost 25 per­cent test pos­i­tive for non-alcohol drugs; of those, about 12 per­cent test pos­i­tive for cannabis. Brian Palmer is Slate’s chief explainer. He also writes How and Why and Eco­logic for the Wash­ing­ton Post. Fol­low him on Twit­ter. Source: Slate Mag­a­zine (US Web) Author: Brian Palmer Pub­lished: May 1, 2014 Copy­right: 2014 The Slate Group, LLC. Con­tact: letters@​slate.​com Web­site: http://​www​.slate​.com/

995b97dbfcsary1.jpeg 150x99 How Bad Is Marijuana for Your Health?

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How Bad Is Mar­i­juana for Your Health?

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