SEATTLE — Marijuana remains illegal under federal law, but that has not stopped a fuzzy industry of marijuana farms and dispensaries from rising to serve the 15 states that allow the drug to be used for medical purposes. Under President Obama, the federal government had seemed to make a point of paying little attention — until now.

As some states seek to increase regulation but also further protect and institutionalize medical marijuana, federal prosecutors are suddenly asserting themselves, authorizing raids and sending strongly worded letters that have cast new uncertainty on an issue that has long brimmed with tension between federal and state law.

How can a drug that federal drug law says is criminal be considered medicine under state law?

“It’s weird,” said Kevin Griffin, co-founder of West Coast Wellness, a medical marijuana dispensary that opened here in February. “We’re not a pharmacy. We spent a lot of time gathering information, and this is what we came up with as the most responsible, legal way.”

Posters featuring Pink Floyd and Tupac Shakur lined the white walls of the office, in the back of a bland building just inside Seattle’s northern boundary. Glass pipes decorated a shelf. And then there was the medicine, available by “donation only,” which included less expensive “medibles” like lollipops and “pot” pies and the traditional smoked dosages at about $280 an ounce. Questions? Just ask the “budtender” — while you still can.