Federal drug investigators can't access an Oregon-maintained database that records patients' prescription information without first getting a warrant, a federal judge in Portland ruled.

In the opinion issued Tuesday, Senior U.S. District Judge Ancer Haggerty sided with the American Civil Liberties Union in declaring that patients have a reasonable expectation to privacy of their prescription drug information, even if it is then forwarded to Oregon's Prescription Drug Monitoring Program. Federal investigators must prove probable cause to a judge before being able to access the state's database, he said.

“It is more than reasonable for patients to believe that law enforcement agencies will not have unfettered access to their records,” Haggerty wrote in the opinion. Prescription drug data is “intensely private,” he said.

He noted the ACLU’s examples of two patients whose prescribed regimen of testosterone reveals they are undergoing hormone treatment for a gender-identity disorder. “It is difficult to conceive of information that is more private or more deserving of Fourth Amendment protection,” the judge wrote.

The decision comes after the state sought federal court guidance on whether it needed to turn over information kept by the Prescription Drug Monitoring Program to Drug Enforcement Administration agents without a court order. Created in 2009 and designed to combat prescription drug abuse, the program requires pharmacies to submit the names, addresses and other information for patients who receive prescriptions containing oxycodone, methadone, codeine, testosterone and certain other drugs.

The DEA argued that an administrative subpoena -- which does not require a judge's approval -- was sufficient to demand information relevant to investigations into potential drug violations, such as a doctor who improperly prescribes drugs. Oregon’s database is useful because it consolidates all of the state's prescription-drug information in one place, Assistant U.S. Attorney Kevin Danielson said in court filings.

The ACLU hailed Haggerty’s decision as “a total victory for the privacy rights of patients” in Oregon -- and potentially beyond. Haggerty’s decision is the first time a federal judge has required the government to obtain a warrant before accessing such state-maintained prescription drug databases, said ACLU staff attorney Nathan Wessler, who argued the case. Every state except Missouri and the District of Columbia have some type of prescription drug monitoring database, he said.

He said requiring the agency to obtain a warrant will also help guard against “invasive investigations on a hunch” -- as opposed to being based on probable cause of a drug violation.

“I would expect the federal government to take this ruling seriously throughout the country,” he said.

Oregon’s database is designed to cut down prescription drug abuse and overdoses by letting pharmacists and doctors quickly see whether a patient is securing and filling multiple prescriptions for the same drug.

Since the program’s creation, the DEA has submitted at least three administrative subpoenas, according to court filings. In one September 2012 request, it sought one year’s worth of records for all controlled substances prescribed by two unidentified doctors, including the names, addresses and payment methods for the patients for whom the prescriptions were written.

The subpoena also instructs the state not to alert anyone to the disclosure of such information.

The state, which filed suit in 2012, complied with one of the agency’s requests after a U.S. magistrate judge issued a court order on the DEA’s behalf.

In an email, a spokesman for the Oregon Department of Justice said the state does not have "a categorical problem with DEA obtaining information from the program. But we feel it is important that they comply with the law in order to get it."

An attorney for the DEA did not immediately comment.

-- Helen Jung