Chicago Sun-Times - - WELL - BY DR. ROBERT ASH­LEY Dr. Robert Ash­ley is an in­ternist and as­sis­tant pro­fes­sor of medicine at the Univer­sity of Cal­i­for­nia, Los An­ge­les.

Dear Doc­tor: Can mar­i­juana use re­ally in­crease the risk of high blood pres­sure, as a re­cent study sug­gests? I thought mar­i­juana was sup­posed to make you re­lax.

Dear Reader: If you’ll re­call, there was a time when smok­ing to­bacco was sim­i­larly touted as a healthy way to re­lax. Only af­ter years of study and na­tional ed­u­ca­tional cam­paigns did the pub­lic be­gan to re­al­ize the detri­ments of to­bacco. Today, in the de­sire to le­gal­ize mar­i­juana, pro­po­nents have fo­cused on its po­ten­tial health ben­e­fits. That doesn’t mean it has no neg­a­tive ef­fects.

In fact, smok­ing mar­i­juana leads to an in­crease in heart rate, in­creased con­trac­tion of the heart and a small in­crease in blood pres­sure. The 2017 Euro­pean Jour­nal of Pre­ven­tive Car­di­ol­ogy study you men­tioned at­tempted to quan­tify these neg­a­tive ef­fects.

The data used in the study come from a na­tional sur­vey in 2005 in which peo­ple over the age of 20 were asked: “Have you ever used mar­i­juana or hashish?” Par­tic­i­pants who an­swered “yes” were termed “mar­i­juana users.” The au­thors also asked the year that peo­ple first used mar­i­juana, from which they cal­cu­lated to­tal years of use. The au­thors then looked at mor­tal­ity data from 1991 to 2011.

In this study, 56.5 per­cent of the 1,213 el­i­gi­ble par­tic­i­pants were qual­i­fied as mar­i­juana users. Note that 63 per­cent of these “users” also had a his­tory of smok­ing to­bacco. The over­all death rate of mar­i­juana users was 29.7 per­cent, while in non- users the rate was 26.2 per­cent. The au­thors found that the death rate from high blood pres­sure was 4.3 per­cent higher in the users of mar­i­juana, but they didn’t find a dif­fer­ence in death rates from heart at­tacks or strokes.

But let’s look at the ma­jor prob­lems with this study. First, the def­i­ni­tion of “mar­i­juana user” was prob­lem­atic. Peo­ple who used mar­i­juana once in their life­time were quan­ti­fied as mar­i­juana users. The data didn’t dif­fer­en­ti­ate be­tween some­one who had used mar­i­juana ev­ery day for the last 20 years and some­one who used it once in col­lege. Next, the num­ber of par­tic­i­pants was rel­a­tively small, which af­fects the con­clu­sive­ness of the find­ings. For ex­am­ple, in this study, cig­a­rette smok­ers had less risk of dy­ing from a heart at­tack than did non­smok­ers. That runs counter to large tri­als show­ing the op­po­site. Lastly, many of the mar­i­juana smok­ers also smoked cig­a­rettes— so if the data about cig­a­rette smok­ers were in­ac­cu­rate, as the sus­pect find­ing sug­gests, there may be fur­ther in­ac­cu­ra­cies in the data.

How­ever, the study does high­light that mar­i­juana users had a higher rate of high blood pres­sure. This was also found in a 2016 study show­ing a mild el­e­va­tion of blood pres­sure in mar­i­juana users. Among peo­ple who used mar­i­juana one to six days per month, the sys­tolic blood pres­sure was el­e­vated by 1.3 points on av­er­age, and among those who used 21 to 30 days per month, the sys­tolic blood pres­sure was el­e­vated by 2.6 points on av­er­age.

All these data point to how poorly we un­der­stand the health con­se­quences of mar­i­juana use. For ex­am­ple, we sim­ply don’t know whether mar­i­juana smok­ing has the same neg­a­tive vas­cu­lar ef­fects as to­bacco smok­ing. With less fear of in­car­cer­a­tion over mar­i­juana use, per­haps more peo­ple will par­tic­i­pate in larger stud­ies to as­sess mar­i­juana’s ef­fect upon the car­dio­vas­cu­lar sys­tem.

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