Andrew Feldmar, a Vancouver psychotherapist, was on his way to pick up a friend at the Seattle airport last summer when he ran into a little trouble at the border.

A guard typed Feldmar's name into an Internet search engine, which revealed that he had written about using LSD in the 1960s in an interdisciplinary journal. Feldmar was turned back and is no longer welcome in the United States, where he has been active professionally and where both of his children live.

Feldmar, 66, has a distinguished resume, no criminal record and a candid manner. Though he has not used illegal drugs since 1974, he says he has no regrets.

"It was an absolutely fascinating and life-altering experience for me," he said last week of his experimentation with LSD and other psychedelic drugs. "The insights it provided have lasted for a lifetime. It allowed me to feel what it would be like to live without habits."

Feldmar said he had been in the United States more than 100 times and always without incident since he last took an illegal drug. But that changed in August, thanks to the happenstance of an Internet search at the Peace Arch border station in Blaine, Wash.

The search turned up an article in a 2001 issue of the journal Janus Head devoted to the legacy of R.D. Laing, with whom Feldmar had studied in London about 30 years before.

"I traveled to many regions many times with the help of many different substances," Feldmar wrote of his experiences with Laing and other psychiatrists and therapists. "I took peyote, psilocybin mushrooms, cannabis" and other drugs, he added, "but I kept coming back to LSD."

He was asked by a border guard whether he was the author of the article and whether it was true. Yes, he replied. And yes.

Feldmar was held for four hours, fingerprinted and, after signing a statement conceding the long-ago drug use, sent home.

Mike Milne, a spokesman for the Customs and Border Protection agency in Seattle, said he could not discuss individual cases for reasons of privacy. But the law is clear, Milne said. People who have used drugs are not welcome here.

"If you are or have been a drug user," he said, "that's one of the many things that can make you inadmissible to the United States."

He added that the government was constantly on the hunt for new sources of information. "Any new technology that we have available to us, we use to do searches on," Milne said.

Feldmar has been told by the American consul general in Vancouver that he may now enter the United States only if he obtains a formal waiver.