A few weeks ago, voters in Colorado and Washington approved ballot initiatives that legalized smoking or otherwise consuming marijuana. In a few weeks, people 21 or older will be able to buy up to an ounce of marijuana for recreational use. While I have no personal objections to marijuana use, there are a few things to keep in mind before you plan a day trip from Utah to Colorado, or book a flight to Seattle.

First, marijuana use is still illegal under federal law, and the laws in Colorado and Washington don’t change that. Local law enforcement officials should be enforcing the laws of their states and not the laws of the national government, but it is still possible for federal agents to arrest a suspect and prosecute them in federal court. The punishments for federal crimes tend to be stiffer than the ones states impose. If you only purchase the small quantities that will be legal under Colorado and Washington law, you are unlikely to catch the attention of federal agents, but there is always the chance you will be an unlucky person snagged in a larger drug bust.

Second, you could get a DUI conviction here in Utah, even if you are no longer high or otherwise impaired. This can be shocking for many people to discover they can be prosecuted for something that did not affect their driving. THC—the active ingredient in marijuana—leaves behind small molecules in the blood that are detectable for up to two weeks. Anyone caught is subject to a DUI under Utah Code 41-6a-517, sometimes called a “metabolite DUI.” The punishments for a metabolite DUI are slightly different from a traditional DUI, but you’re still going to be facing some serious consequences, including the suspension of your driver’s license for 4 months.

That is not to say that you have no case if you are accused of a metabolite DUI. Police officers must have a reason for pulling you over, and must follow proper procedures before obtaining a blood sample. Inexperienced or careless officers often make mistakes or ignore constitutional rights. Having an attorney fight for you is the best way to get the best possible outcome for your case.