There are dozens of studies and decades of research indicating how alcohol affects the human body and at what blood alcohol concentrations a person can no longer safely operate a vehicle. However, there has been a proliferation of drug-related DUIs in the past decade, and with many states legalizing or creating a controlled pharmaceutical system for marijuana, there is a correlating need to understand how marijuana alters a person’s judgment, perception, and motor skills—aside from creating uncontrollable urges to eat cupcakes and Cheetos!

In the recent National Highway Traffic Safety Administration publication Drug and Alcohol Crash Risk, researchers note that aside from alcohol, “[m]arijuana is the most frequently detected drug . . . in crash-involved drivers as well as the general driving population.” But what is the actual increased risk of being in an accident if someone has used marijuana? According to a study conducted in 2012 by Mu-Chen Li et al., Marijuana Use and Motor Vehicle Crashes, drivers with active THC in their system were approximately 2.66 times more likely to get into a crash than a drug-free driver. But when NHTSA researchers factored in the drivers’ ages and genders and assessed whether the driver also had alcohol in their system, there was no across-the-board increased crash risk.

One concern highlighted by the study is the combined use of alcohol and marijuana. Psychology Today notes that the two are often used simultaneously, and the effects of each are increased by doing so. One reason for this is that “combining the two may cause individuals to over-use both substances.” One side effect of using the two together is “greening out,” becoming ill, sweating, feeling nauseous, and getting dizzy. Marijuana also increases appetite while preventing vomiting, which is an extremely dangerous combination for someone with alcohol poisoning.

So do these findings give drivers license to light up and get behind the wheel worry-free as long as they haven’t been drinking? Nope. First, Arizona only allows marijuana use on a medical basis, meaning that the user must register with the state and have a valid prescription from a doctor. Possession without a medical marijuana card can be charged as a felony. You can also be charged with a drug-related DUI if you are driving with any amount of THC or its impairing metabolite in your system. These compounds are indicative of marijuana’s psychoactive effects on the human body. These compounds will often remain in the body for multiple hours after a person uses marijuana and in frequent users, can remain for much longer.

No matter what you’re doing, remember that any time you are driving, there are innumerable other people on the road who can be affected by the decisions you make. Be safe out there!