Legalization of Recreational and Medical Marijuana: What We Don’t Know

As I sit here and read the latest report on smoking from the Surgeon General’s office, I can’t help but wonder what the next few decades will reveal about the effects of smoking various other substances (eg, marijuana, cocaine, methamphetamine, bath salts). January 2014 marked the 50th year of the Surgeon General’s Advisory Committee report on the health impact of smoking.1 This report highlighted the potential health risks associated with smoking and the progress that had been made to reduce tobacco use and its impact on disease and death. Our country is starting on a different path related to the smoking and ingestion of marijuana for medical and recreational purposes. The medical use of marijuana has been legally accepted within various states, but not at the federal level. During the past year, several states (eg, Colorado and Washington) have begun the implementation process for the legalization of recreational marijuana, despite the drug still being classified as a Schedule I substance by the federal government.2–4 This means that all pharmacists need to be aware of the local, state, and federal laws that apply to marijuana use in their practice location, so they can help patients understand their legal risk if they choose to use marijuana for medical or recreational reasons. This change in the public’s attitude toward the use of marijuana raises many questions: What are the drug–drug interactions associated with more frequent use of marijuana? What are the health consequences of smoking marijuana on pulmonary disease and cancer? Will there be a Surgeon General’s report on the health consequences of marijuana use in 10, 25, or 50 years? Drug–drug interactions are a concern with all drugs, but they can pose a potential risk when patients do not report all the drugs they are using during a medication history. Marijuana is one substance that is not commonly reported by patients. They may not report it even when its legal status changes. Potential drug interactions with marijuana include antidepressants, lithium, barbiturates, muscle relaxants, anticholinergics, cocaine, disulfiram, naltrexone, ethanol, protease inhibitors, sildenafil, theophylline, warfarin, opioids, and central nervous system depressants.5–7 Some of the drug interactions are pharmacokinetic and others result in pharmacologic changes. It may be worthwhile for pharmacists to check whether their drug interaction software program can detect any of these potential drug interactions or even recognizes marijuana as a drug. Marijuana is used and produced in many ways. It is estimated that marijuana contains more than 460 active chemicals and over 60 unique cannabinoids. The concentration of the various ingredients varies from plant to plant and batch to batch and will also differ based on where the plants were grown. Routes of administration (eg, dried and smoked, cooked in food, inhaled through a vaporizer, or applied as a topical balm) will influence the rate and amount of drug absorbed.6,8–10 Patients may observe differences between the various products or routes of administration, and they should be aware of this possibility. Like all other drugs, marijuana use is associated with adverse reactions. These include altered central nervous system responsiveness, dry mouth, drowsiness, sedation, blurred vision, dry eyes, reddening of the conjunctiva, mydriasis, photophobia, changes in psychological function, dyspnea, vomiting, and weight gain.7,9,11 It has not been adequately established whether marijuana is associated with causing chronic bronchitis symptoms and large airway inflammation and cancer, especially lung cancer, but these effects are thought to be possible.12–15 Will there be a Surgeon General’s report on the health consequences of marijuana use in 10, 25, or 50 years? It is unlikely, because the majority of patients will not be ingesting or smoking the drug as frequently as cigarettes, but you never know. Pharmacists should consider all of these issues in their evaluation of patients’ medication profiles and in answering patients’ questions related to drug–drug interactions and the medical consequences of using marijuana for recreational or medicinal purposes. When obtaining medication histories, pharmacists should ask all patients whether they use marijuana and, if so, how often and by what route. This information should be entered into the patients’ records so it can be screened by the drug interaction program for potential interactions with other medications. Without this type of screening and record keeping, we are doing our patients a disservice.