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Alert Diver is the dive industry’s leading publication. Featuring DAN’s core content of dive safety, research, education and medical information, each issue is a must-read reference, archived and shared by passionate scuba enthusiasts. In addition, Alert Diver showcases fascinating dive destinations and marine environmental topics through images from the world’s greatest underwater photographers and stories from the most experienced and eloquent dive journalists in the business.

RESEARCH, EDUCATION &

RESEARCH, EDUCATION & MEDICINE EXPERT OPINIONS Marijuana and Diving By Hillary Viders, Ph.D. THC metabolites may persist in the body for days or weeks after marijuana use. The ongoing effects of these metabolites on reflexes and cognition are not well understood. LATTA PICTURES/ISTOCKPHOTO.COM Marijuana (cannabis) is one of the most commonly used recreational drugs in the world. In 2015 a Pew Research Center survey found that almost half of Americans claim to have used marijuana at some point in their lives. 1 According to the 2014 National Survey on Drug Use and Health (NSDUH) prepared for the Substance Abuse and Mental Health Services Administration (SAMHSA), some 22 million Americans ages 12 and older smoked marijuana in a single month that year. 2 Marijuana, like heroin, is a Schedule I controlled substance in the U.S., a classification reserved for what the government considers to be the most dangerous drugs. 3 The Drug Enforcement Administration (DEA), however, recently revealed that it plans to decide this summer whether marijuana should be removed from that list. 4 Four states — Colorado, Washington, Oregon and Alaska — and the District of Columbia have already passed measures to legalize marijuana for recreational use. U.S. Surgeon General Vivek Murthy, M.D., told CBS This Morning in February 2015 about his stance on marijuana legalization: “We have some preliminary data showing that for certain medical conditions and symptoms, marijuana can be helpful.” In a statement issued by the Department of Health and Human Services, he added, “Marijuana policy — and all public health policies — should be driven by science.” 5 Marijuana for medical use is currently legal in 25 states, the District of Columbia and Guam. It is prescribed to treat a variety of severe and debilitating ailments including multiple sclerosis, muscular dystrophy, terminal cancer, AIDS, Crohn’s disease, Parkinson’s disease, inflammatory bowel disease, severe or chronic pain and glaucoma, 6 and it is currently being studied for use in treating posttraumatic stress disorder (PTSD). 7 In Canada, Prime Minster Justin Trudeau has asked the Minister of Justice and Attorney-General Jody Wilson-Raybould to “create a federal-provincial-territorial process that will lead to the legalization and regulation of marijuana.” 8 As marijuana legalization proceeds in the U.S. and Canada, the number of people, including divers, using marijuana may increase. Scuba divers are already smoking marijuana in significant numbers and without any guidelines about 48 | SUMMER 2016

smoking and diving practices. In 2011 Marguerite St Leger Dowse and colleagues published a survey of recreational divers in the U.K. who used illicit drugs, including marijuana. Of the 479 divers who responded, 105 (22 percent) reported using illicit drugs since they first learned to dive, and of those 105, 99 (94 percent) had used marijuana. 9 With this data in mind, there are questions about marijuana and diving that warrant answers. To date, marijuana research in the United States has been very difficult because of marijuana’s classification as a Schedule I drug, Those restrictions may change if the government downgrades marijuana to a lower category. In the meantime, we ask the experts. What are the most immediate concerns with regard to marijuana use and diving? Paul Auerbach: When considering the effects of marijuana on divers, a number of issues come to mind. There are acute and chronic effects that may influence a diver’s mental state, judgment and physical reflexes as well as perhaps relevant cardiovascular, neurological and other physiologies. It is dictum that anything that might impair a diver underwater is detrimental and forbidden, unless there is a benefit that supersedes the negative effects. We know virtually nothing about the effects of marijuana use in divers, but there is scientific literature on the use of marijuana above water from which we can reasonably extrapolate. Common sense dictates that the onus is on the science community to prove that marijuana use in any form or quantity in divers is safe, rather than to take a position that it should be considered safe until proved otherwise. Tom Neuman: In a laboratory setting, marijuana clearly reduces a number of motor and cognitive skills and thus, if one can extrapolate from the laboratory setting to real-life situations, the use of marijuana prior to diving (i.e., diving while “high”) would be problematic. Are people who are ill enough to warrant medical marijuana fit enough for diving? Steven Gillon: It depends on why they are taking marijuana and the degree to which they have a specific condition. I prescribe medical marijuana for patients with severe illnesses such as Crohn’s disease, irritable bowel syndrome and intractable pain. There are many other indications as well. Some of these illnesses are controlled, while others are not, and of course those situations preclude diving. I would also strictly advise against marijuana use and diving for anyone with cardiovascular or pulmonary disease or compromised vestibular function until they are appropriately assessed for fitness to dive. Does marijuana have an adverse effect on a diver’s lung function, and how does marijuana affect a diver’s cardiovascular system? Ernest Campbell: It is good to answer these two questions together, as lung and cardiovascular functions are closely related. Marijuana smoke, in addition to containing THC and cannabinoids, also has large quantities of tar, foreign bodies and carcinogens (50 percent more than tobacco smoke). The acute effects of smoking marijuana on a diver’s lungs include an increase in size of the terminal bronchi, increase in mucus production, cough, inflammation and loss of function of the ciliated bronchial cells (which clean dust and debris and perform an immune function, reducing infection). This process increases the risk of mucus plugs, air trapping and gas embolism. Chronic smoking can lead to chronic obstructive pulmonary disease, with the concomitant risks of air trapping and gas embolism. Cardiovascular changes that occur with episodic smoking of marijuana include an increase in the heart rate by 30-50 beats per minute, increase in blood pressure and gas changes that can include decreased oxygen and increased carbon monoxide (CO) and carbon dioxide (CO 2 ) with an elevated risk for heart attack and syncope. Small gas changes at the surface become exaggerated with the effects of depth/pressure and may lead to CO poisoning at depth and hypoxia upon ascent. To what extent will marijuana exacerbate nitrogen narcosis? Richard Moon: It is well established that nitrogen under pressure causes cognitive changes and can alter reaction time, judgment and performance in a number of areas. The effects of nitrogen narcosis begin to be most apparent at depths between 80 to 100 feet of seawater, and they become progressively more marked as depth increases. We know that there is interaction between nitrogen and other gasses that can cause cognitive deficits, such as elevated blood CO 2 levels. High levels of oxygen, such as might be experienced with enriched oxygen mixtures such as nitrox, may exacerbate nitrogen narcosis. Marijuana use, which is known to have adverse effects on cognition and ALERTDIVER.COM | 49

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