BOSTON (AP) — Gov. Charlie Baker indicated Friday that he could not support a Senate proposal that calls for screening middle and high school students for potential drug abuse unless it was made optional for school districts with funding made available by the state.

The provision is part of broader legislation being offered by Senate leaders to attack the state's opioid abuse crisis.

The governor told reporters he initially misunderstood the proposal to call for actual drug testing of public school students, something he considered problematic on many levels. The bill in fact would require students in the seventh and tenth grades to be asked questions by qualified screeners, such as school nurses, guidance counselors or psychologists, to determine if they are at risk for dangerous behavior.

If done right, the governor said such a program could help the state and local communities develop strategies to curtail opioid addiction among young people. But he made clear he would not accept making it mandatory for school districts.

"I'm not wild about unfunded mandates," said Baker. "I certainly support the idea of having the state provide support for communities that wish to participate in this, (but) unless we as a commonwealth choose to pony up the money to pay for a program like that I don't think it's fair or appropriate for us to just tell locals to do anything."

The governor was asked about the Senate bill during a news conference in which he urged Massachusetts residents to turn in unwanted or unused prescription medication during National Prescription Drug Take-Back Day on Saturday.

A spokesman for Senate President Stan Rosenberg said that while the legislation, scheduled for floor debate next week, does not specify a funding source for the screening program, communities would likely be able to tap into $27 million that has been set aside for opioid abuse prevention in a separate spending bill.

Baker also alluded to the $27 million as a possible source of funding for school districts that choose to adopt the new screening protocols.

Officials cited the wave of deadly overdoses from heroin and other opioids as giving new urgency to the drug take-back effort. More than 170 sites in Massachusetts will accept drop-offs of prescription drugs — excluding liquids or needles — between 10 a.m. and 2 p.m. on Saturday.

Residents were urged to go through their medicine cabinets and clear out unwanted or expired drugs.

Michael Ferguson, special agent in charge of the New England office of the Drug Enforcement Administration, said addiction often begins with abuse of prescription painkillers found right at home.

"Pill addiction is the gateway to heroin addiction," he said.

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Online: Massachusetts drug take back locations: http://www.mass.gov/eohhs/feature-story/dea-takeback-program-massachusetts-locations.html