The measure, passed on a 95-1 vote Friday, defines marijuana as part of the cannabis plant containing more than 0.3 percent of delta-9 THC and THC acid. Supporters said the change was a technical fix needed to help police and prosecutors distinguish marijuana from industrial hemp, which is grown for its fiber.
The bill now heads to the Senate.
The recreational marijuana law currently defines marijuana only by its content of the intoxicating compound delta-9 THC. Scientists with the state crime lab say that often, even potent marijuana can have less than 0.3 percent of delta-9.
It's only when heated or burned that THC acid turns into delta-9 THC, and they argue that marijuana should be defined by the combined amounts of both compounds.