SAN JOSE — The Main Jail on Hedding Street was locked down Wednesday afternoon after at least four inmates overdosed on illicit drugs.

The inmates were taken to Santa Clara Valley Medical Center for treatment. All four are expected to recover, Sgt. Rich Glennon said.

A source familiar with the investigation said two inmates are being discharged back to jail, and the other two are conscious and expected to recover.

During the lockdown, inmates are restricted to their cells and no visitors are allowed while correctional officers search for the source of the drugs.

They could have been smuggled in, or have been prescribed medications that inmates got from the medical staff, hoarded and either ground up to snort or shoot, or ingested.

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Correctional deputies do not carry or administer Narcan (naloxone), an emergency treatment that blocks the effects of opioids and can reverse an overdose, Glennon said. He said it was unclear whether the jail medical staff had the antidote on hand.

Normal jail operations are expected to resume tonight, Glennon said.

Check back for updates.