How to Travel With Medical Marijuana

This fall, Sierra Riddle queued up at security at Los Angeles International Airport with a tincture bottle of THC oil — the psychoactive ingredient in cannabis — in her purse.

Ms. Riddle, 31, a nursing assistant from southern Oregon, was traveling with her son Landon, 9, and uses medical marijuana to treat his severe nerve pain from chemotherapy, as well as her own chronic pain. She was on her way to a medical conference in Dallas to talk about her son’s medical marijuana use and was “praying and meditating that we’d make it through security,” when a Transportation Security Administration agent pulled the bottle out of her bag.

“It’s just botanical oils,” Ms. Riddle said she told the officer. “But this was L.A. — they’re hip to the game and so they knew what is was.”

To Ms. Riddle’s surprise, the officer told her that, while it’s illegal to fly with marijuana and he was obliged to call the police, instead, he would just throw the bottle in the trash and wouldn’t report her.

With 33 states now allowing some form of medical marijuana, it might seem that traveling with medical marijuana should be easy enough. But there’s a difference between state governments and the federal government, and if you don’t know the rules, traveling with medical marijuana could lead to an arrest or at the very least, a complicated legal gray area.

In the United States, the federal government still classifies marijuana, even medical marijuana, as a Schedule I controlled substance, which means anyone transporting it across state lines is committing a federal crime and can be charged with drug trafficking. This carries a minimum penalty of up to five years in prison and a $250,000 fine for the first offense.

Internationally, fines and punishments for marijuana possession can be much harsher, including long jail sentences or even execution for trafficking large amounts.

The T.S.A. says it’s not interested in finding your medical marijuana.

“We’re focused on security and searching for things that are dangerous on the airplane,” said Mark Howell, a T.S.A. regional spokesman. Even though the T.S.A. is a federal agency, and it can often feel as though agents are overly zealous about checking your bags, “we’re not actively looking for marijuana or other drugs,” Mr. Howell said.

Careful: Though a recent Instagram post by the T.S.A. notes that while “T.S.A. officers DO NOT search for marijuana or other illegal drugs,” if they do find it, they are required by federal law to turn it and the owner over to local law enforcement.

In a state where medical marijuana is legal, Mr. Howell added, “you present your medical marijuana card, and the law enforcement officials will usually just give it back to you.”

You should also look up your airline’s rules and regulations: Many carriers, including Delta Air Lines, Alaska Airlines and American Airlines have created policies that ban medical marijuana (THC) from their aircraft, even if you have a medical card.

Know the laws of the states you are traveling to or through: Even if you have a medical marijuana card, you can be arrested and charged for possession in states where medical marijuana is not legal.

Nearly 20 states accept out-of-state medical marijuana authorizations, but reciprocity laws vary from state to state.

In some states, like Arkansas, visitors are required to sign up for the medical marijuana program 30 days in advance and pay a $50 nonrefundable fee. Visitors should also keep in mind the state’s purchasing limit, which can be different for residents versus those who are there temporarily. In Oregon, for example, residents can possess up to 24 ounces, while visitors are allowed only one ounce.

Amtrak’s policy is strict: “The use or transportation of marijuana in any form for any purpose is prohibited, even in states or countries where recreational use is legal or permitted medically.”

Greyhound Lines bans alcohol and drugs “anywhere on the bus (including in your checked baggage).”

If you choose to drive with medical marijuana, be discrete. Many marijuana arrests begin as traffic stops, according to Americans for Safe Access, a nonprofit advocacy group. They recommend keeping cannabis locked in your trunk and never driving under the influence. You should never carry medical marijuana in a state where it’s not legal.

In May, the T.S.A. updated its rules for flying with medical marijuana, allowing travelers to now carry products like Cannabidiol oil that contain less than 0.3 percent THC. Cannabidiol, or CBD, is a molecule in cannabis that does not get patients high. Passengers can bring products that are approved by the F.D.A. in their checked or carry-on luggage.

Don’t forget all your official documents.

“We tell patients to bring their doctor recommendation with them, just in case law enforcement stops them,” said Debbie Churgai, the interim director of Americans for Safe Access.

“We also tell them to keep their medical recommendation and their medical I.D. card with them, and know their physician’s number and maybe their lawyer’s number — just in case.”