The human body constantly works to keep its core temperature near 98.6°F (37°C). The hypothalamus acts as the internal thermostat, adjusting blood flow, sweating, and shivering to prevent dangerous swings. On land, the body primarily loses heat through radiation to the air and convection when wind moves across the skin. Evaporation from sweat is also a major cooling tool, especially in warm environments. These systems function reasonably well on shore, but once someone steps onto a boat or into open water, the physics of heat exchange shift dramatically—especially when cannabis is added to the mix.
Water is a much stronger conductor of heat than air. Research in environmental physiology shows that still water can pull heat away from the body more than twenty times faster than still air at the same temperature. This is why swimmers can become dangerously cold in water that seems comfortable at first. U.S. Coast Guard and CDC guidance repeatedly note that immersion in water below roughly 70°F (21°C) significantly increases the risk of hypothermia, even if the surrounding air feels mild. Wet clothing, wind, and spray on a moving boat amplify this cooling effect, making it possible for core temperature to drop before someone realizes it.
In hot weather, the situation reverses. Sunlight reflects off the water and metal boat surfaces, intensifying radiant heat. Humidity near the water reduces the effectiveness of sweating, which the CDC identifies as the body’s primary method of cooling. When evaporative cooling slows, core temperature can rise more quickly, especially during prolonged exposure or physical activity.
THC complicates these natural systems. Cannabinoids interact with the hypothalamus and can alter thermoregulation in a dose-dependent way. Higher doses of THC tend to lower core temperature, while lower doses may slightly raise it. Research also shows that THC induces peripheral vasodilation: blood vessels widen, making the skin feel warm or flushed even when the body is losing heat. That altered perception can mislead someone about how hot or cold they truly are. THC also changes heart rate and blood pressure, which can put extra strain on the cardiovascular system when the body is already fighting to cool down or warm up.
On the water, these effects take on added importance. In cool or cold conditions, THC’s tendency to promote heat loss can make immersion more dangerous. A person who is high may underestimate how cold they are, stay in the water longer than is safe, or fail to recognize the early signs of hypothermia. Impairment also affects coordination and judgment, which are essential for swimming, climbing back aboard, or responding quickly in an emergency.
In hot conditions, THC can distort the feeling of heat, encouraging someone to stay in the sun too long or skip hydration breaks. Dehydration inhibits sweating, reduces blood volume, and makes it harder for the body to cool itself. Agencies studying heat illness emphasize that these factors can progress to heat exhaustion or, in severe cases, heat stroke. If someone is high, the chances of overlooking early symptoms—such as dizziness, headache, or confusion—can increase.
Whether the risk is heat or cold, the common thread is that cannabis can change both temperature perception and physiological responses. When combined with the unique environment of open water, that creates situations in which heat-related or cold-related illnesses become more likely. For anyone choosing to use cannabis around boats or water activities, staying aware of weather conditions, hydration, immersion risks, and personal limits is critical for maintaining safety.