The East Coast calls it getting “twisted.” The West Coast calls it getting “crossfaded.” Scientists just call it raising your odds ratio for life-threatening injury. A new study finds consuming any dose of alcohol after using cannabis increases the concentration of tetrahydrocannabinol (THC), the main psychoactive ingredient found in weed, in the user’s blood.

Marijuana use has seen unprecedented growth in the U.S. in the last decade, as several states have decriminalized public use and many more have legalized it for the treatment of chronic conditions related to pain and inflammation. However, the trend still draws criticisms for the public health effects that, by and large, are still unknown.

Accidents are the fifth-leading cause of death in the U.S., and motor vehicles account for more than half of those, according to data from the Centers for Disease Control and Prevention. Scientists, meanwhile, have come to agree that while alcohol and marijuana each raise a driver’s risk for injury independently, doing both is even worse. The latest study may help to explain why.

Dr. Marilyn Huestis, senior investigator at the National Institutes of Health, led a team of researchers in finding out how 19 people reacted to either just alcohol, just cannabis, or a combination of both or neither, which they measured with placebos and at different dosages. They found adding any dose of alcohol increased the amount of THC in the participants’ blood significantly, from a low dose of 32.7 micrograms per liter (µg/L) and high dose of 42.2 µg/L to 35.3 and 67.5 µg/L, respectively.

“The significantly higher blood THC … values with alcohol possibly explain increased performance impairment observed from cannabis-alcohol combinations,” the authors concluded in their report.

The data on marijuana-related car accidents are unfortunately fuzzy. Some evidence suggests the drug is involved in just six percent of cases, while other data suggest the rate could be as high as 32 percent. On the one hand, scientists acknowledge that frequent marijuana users, through practice or simply poor judgment, actually drive more cautiously than sober drivers. But alcohol ruins this cautiousness. Where marijuana gets drivers paranoid about their recklessness, alcohol makes them feel invincible.

Combining the two is a point of study Huestis and her team argue is still up for grabs. “Our results will help facilitate forensic interpretation and inform the debate on drugged driving legislation,” they wrote. With the science of intoxication at hand, experts will be able to better analyze the drug levels in a driver’s blood to help them figure out what went wrong.

On a wider scale, the data could bolster what is otherwise middling information on alcohol’s relationship to a drug that is commonly arriving as a package deal. With falling costs to buy cannabis, increasing potency, and relaxing attitudes, scientists hope their rush to gather important data can outpace the destructive, albeit innocent, decision to indulge.

Source: Harman R, Brown T, Milavet G, et al. Controlled Cannabis Vaporizer Administration: Blood and Plasma Cannabinoids with and without Alcohol. Clinical Chemistry. 2015.