How often a person uses marijuana, how much they use and for how long matters, Gruber said. For example, people may initially experience a rapid heart rate, called tachycardia, from products containing THC. But consistent use may result in tolerance to that effect, often after a few days or weeks.
In clinical studies, researchers measure and control what people are consuming. But because the federal government still classifies marijuana as a schedule 1 substance, meaning it is considered to have a high potential for abuse, researchers face tough restrictions on the products they can give study participants.
The National Institute on Drug Abuse Drug Supply Program provides marijuana for research purposes, Gruber said. But research-grade marijuana isn’t what people are consuming in their homes.
