Almost two years after Texas tried to import an execution drug from overseas, the U.S. Food and Drug Administration ruled Thursday that the drug can’t be admitted into the United States.

In July 2015, the Texas Department of Criminal Justice tried to import 1,000 vials of sodium thiopental, an anesthetic that the state has previously used in executions, but the FDA seized the drugs at a Houston airport and has held them ever since. The federal agency has maintained that the import of the drug is illegal because it is not currently approved in the United States.

In a statement, the FDA said it notified Texas and the Arizona Department of Corrections, which also tried to obtain the drug, that their attempted imports were refused because the drugs appeared to be unapproved and misbranded. The shipments must now be exported or destroyed, according to the agency.

TDCJ spokesman Jason Clark said after the ruling that the department is "exploring all options to remedy the unjustified seizure."

"It has taken almost two years for the Food and Drug Administration to reach a decision which we believe is flawed," Clark said. "TDCJ fully complied with the steps necessary to lawfully import the shipment."

The FDA tentatively decided in April 2016 that the seized drugs couldn't be imported, but no final decision was made until Thursday. In January, Texas sued the agency for what it said was an “unreasonable delay” in deciding if the drugs could be delivered to the state.

"My office will not allow the FDA to sit on its hands and thereby impair Texas’ responsibility to carry out its law enforcement duties,” Texas Attorney General Ken Paxton said at the time in a prepared statement.

As the lawsuit proceeded in the federal court for Texas’ southern district, the FDA announced it would make a final decision on or before Thursday. Asked whether the drugs had expired while being held, the FDA referred questions to the Texas Department of Criminal Justice, which said it was unaware of any expiration date.

Texas has claimed that the import of sodium thiopental was legal because it was being purchased for law enforcement reasons, adding it had received an import license from the federal Drug Enforcement Administration.

Sodium thiopental hasn’t been used in an execution in Texas or the rest of the country since 2011, when the only U.S. manufacturer stopped selling it because of its use in executions. Since 2012, Texas has used a single dose of pentobarbital to put an inmate to death, but with states throughout the country struggling to find execution drugs, it looked to get sodium thiopental just in case.

“We cannot speculate on the future availability drugs, so the agency continues to explore all options including the continued use of pentobarbital or alternate drugs to use in the lethal injection process,” Department of Criminal Justice spokesman Jason Clark said in January.

Clark said last week that the department had no other execution drugs in its inventory aside from 18 doses of pentobarbital, plenty for the five executions currently scheduled.

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