If your holiday plans take you to the parts of the country where recreational marijuana use is now legal \u2014 Colorado, Washington, Oregon, Alaska or Washington, D.C. \u2014 you may be tempted to join the party. Before you do however, it\u2019s important to understand that legal doesn\u2019t mean unrestricted. Plenty of rules remain regarding cannabis use even in the areas with the most liberal policies, and these can trip you up if you\u2019re not wary. And because marijuana likes to stick around in the user\u2019s system, it has the potential to follow you in unintended ways. There are things to consider, in short, before lighting up or reaching for that edible. Here are a few of the most crucial: \t The laws are confusing, and it\u2019s up to you to know them. Marijuana regulations are a confusing patchwork. The drug remains illegal at the federal level, for example, legal in some states, OK only for medical use in others and completely off limits elsewhere. And even within states, regulations can vary from city to city. When the rules bump up against each other, you can easily become an unintentional scofflaw. Consider Colorado\u2019s ski resorts, for example. More than 20 of them are on U.S. Forest Service land, meaning they are subject to federal law. It\u2019s the same story for the state\u2019s national parks. So while you might have bought that marijuana legally in a licensed retail store in Denver, don\u2019t expect to take your purchase with you skiing at Vail or on that hike at Rocky Mountain National Park. It\u2019s up to you to know the laws in the areas you plan to visit. \u201cIt would be incorrect to assume that the way Oklahoma treats marijuana is the way Texas treats marijuana is the way Colorado treats marijuana and so on,\u201d explained Paul Armentano, deputy director of the National Organization for the Reform of Marijuana Laws (NORML). \u201cPossession and use and cultivation and driving \u2014 all these issues are treated differently from state to state. And if one is engaging in any activity that could potentially carry criminal ramifications, obviously there is some burden on the individual to educate themselves as to what the laws are.\u201d To help, NORML maintains a state-by-state guide to marijuana laws at norml.org\/laws. States and cities that allow recreational marijuana also commonly provide fact sheets about appropriate use on their websites. \t Just because your use was legal doesn\u2019t guarantee you won\u2019t be held liable for it later. Marijuana\u2019s psychoactive ingredient, THC, is fat-soluble, meaning it is excreted from the body slowly. As a result, it can show up on marijuana drug tests long after use, making it tough to determine when a person is actually impaired. A blood test is considered the most accurate measure, and that\u2019s what you\u2019ll likely be asked to submit to if ever suspected of driving under the influence of cannabis. But it\u2019s far from perfect. A 2015 study, for example, showed the presence of THC in the blood of some habitual marijuana users up to seven days after their last smoke. And the National Highway Traffic Safety Administration concludes that \u201cIt is inadvisable to try and predict effects based on blood THC concentrations alone.\u201d A urine test is even more problematic, identifying a THC byproduct that can show up days, weeks, or, in the case of heavy users, even months after marijuana was last consumed. What does this mean for you? Say you vacation in Colorado, enjoy a perfectly legal joint or two, return home and on Monday, you are drug-tested by your employer. A urine test is the norm in such situations, so chances are you\u2019ll test positive. Can the company fire you even though your use took place in a situation where consumption was legal and you are obviously not still impaired? In a word, yes. Or imagine this scenario: You live in Oklahoma, one of several states that considers driving with any amount of marijuana in your system, whether you are impaired or not, as driving under the influence. One weekend, you drive to Colorado, smoke some marijuana, wait four hours for the effects to wear off as recommended by NORML, and drive back. On the way, you\u2019re involved in an accident and fault is at question. The marijuana that shows up in your system may have had nothing to do with the crash, but it may be tough making the case. It\u2019s a worst-case scenario to be sure, Armentano said, and not a common occurrence, \u201cbut certainly I am aware of situations where there is an allegation from the defendant that that is exactly what has occurred \u2014 that they are being punished for their use of cannabis at some much earlier point in time.\u201d \t Edibles are tricky. Edible marijuana products, everything from cannabis-infused brownies to sodas to candy, have proven popular in states with retail marijuana sales \u2014 but they\u2019ve also been problematic. Here\u2019s why: inhaled cannabis goes from the lungs directly to the bloodstream and then passes the blood-brain barrier. The effects are felt almost instantly, are relatively predictable and tend to fade within an hour or so. By contrast, Armentano explained, when cannabis is consumed as food, it must first travel through the stomach and then to the liver, where the THC is converted into a psychoactive metabolite known as 11-hydroxy-THC, which can add to the high. In addition, each person metabolizes THC differently. That means edibles are more unpredictable, their effects can take a couple of hours to kick in and they\u2019ll last longer \u2014 perhaps six to eight hours. If you want to give edibles a try, keep these recommendations in mind: \tPay attention to the serving sizes, which should be clearly marked on the packaging. A single cookie, for example, may represent multiple servings. \tBe patient. When people get into trouble with edibles, it is usually because they don\u2019t feel anything right away and assume they need to eat more. Remember, it may be hours before you feel any effects. Wait it out. \tDon\u2019t drive. The high with edibles is a long time coming and a long time leaving. NORML recommends playing it safe and not driving on a day you consume edible cannabis. \tBe prepared. If you\u2019ve tried inhaled marijuana before, the edible experience is likely to be different. With consumed marijuana, you\u2019re not only feeling the effects of the THC but of the 11-hydroxy-THC. \u201cWhen those two are combined, there is a greater possibility of dysphoria and an unpleasant effect,\u201d Armentano noted. Another thing to note: Public use of marijuana is illegal, even in the states that allow recreational use (although what constitutes \u201cpublic\u201d can vary). Part of the reason for the popularity of edibles is that they can be consumed more surreptitiously than inhaled marijuana. But be aware that it is just as illegal to consume edibles in public as it is to fire up a joint. \t Buy wisely \u2014 and save the alcohol for another day. It\u2019s a common refrain in the current national conversation about marijuana: This isn\u2019t your grandfather\u2019s pot. While it\u2019s true that more powerful strains exist today, it\u2019s also true that marijuana of all THC potency levels is generally available in a legal retail store and should be clearly marked. Ask the staff at the store for recommendations. \u201cProprietors hopefully have educated their staff so they are able to provide answers to consumer questions and potentially tailor their purchases,\u201d Armentano said. Even if you do get more than you bargained for, Armentano noted, \u201cthe bottom line is THC is relatively nontoxic and it is incapable of causing lethal overdose, so regardless of the amount of THC someone consumes, we are really talking about a product that at most is going to make a person feel temporarily uncomfortable.\u201d When consuming your purchase, resist the temptation to pair it with alcohol. Research suggests that alcohol can cause THC levels in the blood to spike, Armentano said. \u201cThere is some sort of interaction going on \u2026 where the effect of the two drugs combined is more dramatic than the drugs administered in isolation.\u201d \t You can\u2019t take it with you. When your trip is over, be sure to dispose of any remaining pot purchases. It\u2019s illegal to transport marijuana across state lines, even from Oregon to Washington, which both allow recreational use. The rules may allow you to \u201cgift\u201d a small amount of your leftovers to someone in your party, but don\u2019t even think about handing off anything to someone who is technically underage. One rule you can count on no matter where recreational marijuana is allowed is that it is legal only for those 21 or older.