Using marijuana and alcohol together greatly increases the amount of THC, marijuana's active ingredient, in the blood, a new study concludes.
Using the two substances together raises THC levels much more than using marijuana by itself.
The researchers say using alcohol and marijuana together considerably increases the risk of car crashes, compared with using marijuana alone.
The study included 19 people who drank alcohol or a placebo in low doses 10 minutes before they inhaled vaporized marijuana in either a low or high dose, Time reports.
When a person drank alcohol, their blood concentration of THC was much higher.
The findings are published in Clinical Chemistry.
A study published last year found teenagers who use marijuana and alcohol together are more likely to engage in unsafe driving, compared with those who use one of those substances alone.
Teens who used alcohol alone were 40 percent more likely to admit they had gotten a traffic ticket and 24 percent more likely to admit involvement in a traffic crash, compared with teens who didn't smoke marijuana or drink. Teens who smoked marijuana and drank were 90 percent more likely to get a ticket and 50 percent more likely to be in a car crash, compared with their peers who didn't use either substance.