Or perhaps they just pack it and travel with it in a way that is subtle enough not to draw attention to it, said Lisa Smith of Seattle. She often travels through airports with marijuana and says many of her friends do as well.

Local airport authorities handle the situation differently in different states. In Florida, where medical marijuana is legal but recreational use is not, few are stopped for possession in the airport, but they do face penalties. Eleven of the approximately 2.8 million passengers who were screened by T.S.A. at Jacksonville International Airport in 2016 were detained for possession of marijuana, said Michael D. Stewart, the airport’s director of external affairs. All were arrested or given a notice to appear in court, he said.

T.S.A. agents with dogs that are sniffing people in line by security checkpoints are looking for explosives, not marijuana. Dogs assisting Customs and Border Protection agents, however, are searching for illicit drugs along with other illegal substances, but only among passengers arriving in the United States on international flights.

“Some people like a glass of wine to relax when they travel,” Ms. Smith said. “I prefer a little marijuana.” It is hard to find in some states, she said, so “it’s easier to bring my own.” Medical and recreational marijuana are legal in Washington State.

Typically she takes loose marijuana in a plastic child-safe pill container. “Only once has a T.S.A. agent pulled the container out of my purse,” she said, “but that was because she was looking for a water bottle that had set off the scanner.”

The agent put the marijuana back, Ms. Smith said. “I don’t think she noticed what it was.”

Ms. Smith said she also traveled sometimes with edible forms of marijuana. “I’ll take a couple of cannabis-infused chocolates or mints and transfer them from their packaging to a container that isn’t labeled as a cannabis product,” she said.

Cy Scott, co-founder of Headset, a marijuana industry data analytics company in Seattle, said the proliferation of new forms of cannabis made it easier to take the substance on a flight.