Motor control is also diminished. “Your brain sees an apple, tells your hand to reach out, wrap your fingers around it, and bring it to your mouth. That [process] is tremendously affected by cannabis,” she says. As a boater herself, Huestis sees significant implications while docking, for example. Besides physiological effects while high, marijuana withdrawal also leads to acute tiredness, compounding the effects of fatigue common after a day on the water.