Mixing alcohol with marijuana increases THC concentration in the blood, a new study reports. The study, published in Clinical Chemistry, followed 19 people as they drank alcohol and smoked marijuana. THC is the main ingredient in marijuana.

The 19 people were asked to drink alcohol and then vaporize marijuana so researchers could analyze how it affected the THC concentration. Researchers found that when the two substances were mixed, there was much more THC in the blood than if someone were to just smoke marijuana. Mixing the two substances is a dangerous combination that could lead to accidents.

Those who drink alcohol are already 40 percent more likely to get a traffic ticket and 24 percent more likely to be involved in a car accident. Adding marijuana into the mix makes it 90 percent more likely to get a ticket and 50 percent more likely to be in an accident.

Neither substance should be used before driving, especially not together.