Legalisation of Cannabis Prompts Reconsideration of Diving Safety Advice
A report published by the Diver's Alert Network (DAN) has revisited the issue of scuba diving safety after the use of cannabis, in light of the drug's recent legalisation for medical and recreational use in a number of different locations worldwide.
After caffeine, alcohol and nicotine, cannabis is the most commonly used recreational drug in the world. Surveys suggest approximately 50 per cent of the population of the United States has used cannabis at some point, and a 2010 study by the UK's DDRC found that out of the 427 UK divers that responded to a questionnaire on the subject, 22 per cent had used an illegal drug since learning to dive, 94 per cent of whom specified cannabis.
The cannabis plant has been used in industry (hemp), and as both a recreational and medical drug for thousands of years. It contains a wide array of chemical compounds, collectively known as cannabinoids (CBDs). The psychoactive tetrahydrocannabinol, or THC, is the CBD most synonymous with the cannabis plant for its intoxicating effect, but other CBDs, including cannabidiol (cannabis oil), act as anti-inflammatory medication and may be beneficial to patients with cancer, Crohn's disease and epilepsy, amongst other conditions.
Whether or not it is safe to dive after using cannabis is a complicated question. The intoxicating effects of THC are well known and similar to those of alcohol: impaired cognitive ability and hand-eye coordination, poor judgement, lack of awareness etc, all of which would be extremely hazardous to diver safety. Most (but not all) medical CDBs do not contain THC and are not intoxicating, but there is little research about what other physiological effects CBDs would have on a diver's body. This raises the question as to whether or not the use of non-intoxicating medical marijuana prior to a dive is hazardous to a diver's health, or more like taking an aspirin.
Previous advice from DAN suggested divers should wait several days, even weeks, after using cannabis, until the drug was no longer detectable in their body. This advice, however, was based as much around the drug's illegality as it was diver safety. Cannabis can be detected in the human body for several weeks, which would prove an employee subject to a random drug test had used an illegal substance, but not that they were necessarily unsafe to dive. According to the new report, such a zero-tolerance approach to cannabis use 'may be considered a violation of an individual's rights', given that the drug is no longer illegal in some locations.
Judging whether or not a person is fit to dive following excessive alcohol consumption is relatively easy. Alcohol takes a long time to metabolise and remains active in the body long after a person has taken their last drink. If necessary, an inexpensive breathalyser test would show that a person is too impaired to dive. The intoxicating effects of THC do not appear to last as long as alcohol, with the study reporting that 'levels are low enough for normal functioning on land within about two to three hours', although this may be longer depending on the amount of THC consumed. There is no breathalyser test for THC and urine tests show only that a person has recently consumed cannabis, which may or may not have contained intoxicating THC, and the saliva tests which might detect impairment are expensive.
Given that cannabis is now legally available in some locations, DAN's advice focuses on the psychoactive effects of cannabis being 'the main acute safety concern during diving.' The report states that: 'it is advisable that divers stay out of the water for at least eight hours following smoking or ingestion of cannabis cookies or the oil (in case the oil has any THC) to be confident there will be no psychoactive effects. This period should be extended if a large amount was ingested.'