Cannabis and Diving

Revisiting dive safety after legalization


While there are not sufficient studies on diving while under the influence of cannabis, the psychoactive effects of THC from using cannabis or impure CBD oil can affect your performance and increase your risk while underwater.


Cannabis has been known to humans for thousands of years. Researchers believe that it originated in central Asia some 12,000 years ago and that Neolithic people used it widely for its protein-rich seeds, oils and fibers. Some of the earliest reports of its use date to approximately 4000 BCE, when it was actively farmed and considered one of the "five grains" in China.

Likewise, the indigenous peoples of southern Africa commonly used it for many centuries, long before Europeans set foot on the continent. When Dutch explorer Jan van Riebeeck arrived in South Africa in 1652, he documented that "dagga" (the local term) was in use. Centuries ago cannabis was widely used for a variety of medical conditions. Dr. Russell Reynolds, the personal physician of Queen Victoria, published his experiences using cannabis for a range of conditions, and Queen Victoria allegedly used it to ease menstrual pain.



In South Africa, Dutch settlers accepted cannabis into general use, and the Dutch East India Company traded it before its use was banned in the 1920s. Almost 100 years later, parts of the United States, along with Canada, South Africa and other countries have legalized the personal and private use of cannabis. With legalization comes questions about the safety of diving while using cannabis and cannabidiol (CBD) oil.

When considering CBD oil in isolation, the short (but possibly incorrect) answer to the safety question is that it has no effect, because CBD is not psychoactive and would not likely affect dive safety. Not all formulations of CBD are pure, however; some may contain delta-9-tetrahydrocannabinol (THC), which is indeed psychoactive. The body metabolizes THC, forming more than 100 metabolites (substances resulting from metabolization), some of which (such as hydroxyl-THC) are also psychoactive.


The current tests available for intoxication versus nonactive substances from using cannabis are not sufficient to determine the level of impairment for a driver.
Similar to diving while under the influence of alcohol, diving while under the influence of THC and related substances is risky. Extrapolation from reports of motor vehicle accidents after cannabis use provides some useful information and guidance. Tests indicate that cannabis use results in deficient tracking, attention, reaction time, short-term memory, hand-eye coordination, vigilance, time perception, distance perception, decision making and concentration. Therefore, cannabis intoxication during a dive will alter perception of the environment and impair both cognitive and psychomotor performance.

Many divers use cannabis, although insufficient data exist concerning diving while under its influence. A survey of recreational divers in the United Kingdom revealed that of the 479 divers who responded, 105 (22 percent) reported using illicit drugs since they first learned to dive, and 94 percent of those had used cannabis. It is unclear, however, how

Divers should adhere to a conservative waiting period after cannabis use
before diving.
many of these divers were under the influence while diving. A few reports describe affected divers in warm water becoming lethargic and even falling asleep while submerged and divers in cold water finding that their tolerance to cold was reduced. Safety-conscious divers should not ignore this issue.

Testing for the psychoactive effects of cannabis is difficult in recreational diving, regardless of whether you are a dive operator trying to ensure the safety of your operation or a CBD or cannabis user (for recreational or medical purposes) trying to ensure your own safety while diving. Unfortunately, current urine tests for cannabis do not distinguish between the psychoactive and nonpsychoactive metabolites — the only results are positive or negative for the presence of cannabinoids. It is more important from a safety standpoint to distinguish between the psychoactive and nonpsychoactive substances to identify to what extent someone is affected.

For this reason, previous advice about waiting a few weeks to clear the body of all metabolites is inadequate and can now even be considered a violation of an individual's rights if such strict rules are applied. Any zero-tolerance policies should be applied to the active metabolites and not the nonactive ones that can remain in the body for


weeks. The same argument would hold for commercial diving operations that test for cannabis as a part of wider drug screening. The main difference between testing for cannabis use and alcohol use in the context of diving, where zero-tolerance policies are applied to both, is that breathalyzer tests for alcohol detect the active ingredient that causes the impairment, while urine tests for cannabis also detect nonactive metabolites.

The screening that works best to detect if someone is under the influence is a saliva test, which tests for THC, the actual psychoactive substance. The best tests currently available in most countries have a lower detection limit of 40 nanograms per milliliter (ng/mL). Recommended limits for detecting intoxication are 4 ng/mL for screening


tests and 2 ng/mL for confirmatory tests — only 5 or 10 percent of the detectable level. The test is also quite expensive. For these reasons mass testing is not currently effective. If someone tests positive on a saliva test, you can be sure that they are affected at that time because of the THC level required to have a positive result. An operator could then refuse participation because of a safety risk. Such intoxication could also be considered illegal (pending further court decisions), because in many locations cannabis use is legal privately and not in public.

If you are using CBD oil and want to make sure you are safe while diving, look at the label to confirm its purity and lack of THC. Not all manufacturers declare contaminants — particularly if present in low concentrations. There currently is no inexpensive, reliable way of confirming whether someone is affected.

Another way of determining safety is to consider the relatively short half-life of THC in the body. If you can observe enough time between using CBD oil, smoking a joint or eating a cannabis cookie and diving, you can reasonably ensure that it is safe to dive. Unfortunately, we do not have specific values available for the oil, but studies have looked at both smoking and ingesting cannabis.


Figure 1: Mean plasma concentrations of delta-9-tetrahydrocannabinol (THC), 11-hydroxy-TCH (11-OH-THC) and 11-nor-9-carboxy-THC (THC-COOH) of six subjects during and after smoking a cannabis cigarette containing about 34 mg of THC


THC levels drop quite rapidly after smoking cannabis, and the levels are low enough for normal functioning on land within about two to three hours. The red dotted line in Figure 1 represents THC concentration. Driving tests have indicated that impairment is dose dependent and generally lasts for two to four hours. Notice that the nonpsychoactive metabolite THC-COOH remains detectable in the blood and urine for a long period, and we do not know enough about these metabolites' possible effects underwater.


Figure 2: Mean plasma concentrations of delta-9-tetrahydrocannabinol (THC), 11-hydroxy-THC (11-OH-THC) and 11-nor-9-carboxy THC (THC-COOH) of six cancer patients after ingestion of one 15 mg oral dose


Figure 2 shows that with ingestion of cannabis, there is a lower peak, but the half-life is longer (four to six hours). It should be noted that plasma levels differ between people ingesting the same amount of cannabis.

Since the psychoactive effects are the main acute safety concern during diving, and everyone responds differently to the consumption of cannabis, 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. Because of cannabis legalization and the need for employers to ensure health and safety at work, better saliva testing equipment should become available and be more affordable for performing screening tests in the future.

While this article considers only the acute intoxicating effect of cannabis, fitness-to-dive evaluations should consider some of the longer-term effects of cannabis use, including the effects on the lungs from smoking. Discuss any concerns regarding fitness with a physician trained in dive medicine. As with any substance, divers should be aware of the effects and risks of cannabis while diving and take the necessary precautions to use it safely.

© Alert Diver — Q3 Summer 2019