Parents hoping to treat seriously ill children with medical marijuana cheered when Pennsylvania's new law included a "safe harbor" provision allowing them to import the medicines right away, rather than waiting for the law to take full effect in two years.

Legal experts are now saying there may not be much to celebrate.

The fact is, the state can't protect residents from federal laws against moving pot across state borders.

And in Pennsylvania, where it's not yet legal to sell marijuana products, the only way parents can get such drugs is to bring them in.

Still, parents are risking criminal charges and prison sentences if they assume the safe harbor provision shields them, according to marijuana policy experts.

By encouraging people to cross state lines, the Pennsylvania safe harbor provision violates U.S. Department of Justice guidelines that have tacitly allowed state medical marijuana programs to operate, said John Hudak, who researches state and federal marijuana policies at the Brookings Institution.

"Possession of marijuana is a federal offense, crossing a state line with it is another," Hudak said. "You are risking jail time."

A spokeswoman for the U.S. Attorney's Office in Philadelphia said she was not aware of any medical marijuana cases that had been prosecuted in the Eastern District of Pennsylvania.

Some parents worry that despite state assurances, even local law enforcement may not be on board.

Erin McCann of Collegeville said she had considered going to Colorado for marijuana medicines to treat her 12-year-old son's seizures. After weighing the potential downside, she decided against it.

"Nobody has tried to see how D.A.'s will react to the law," she said. "They can still charge you, and you could still incur all the legal fees. I don't want to be the guinea pig."

In 2013, the U.S. Attorney's Office issued recommendations to its regional divisions on how federal marijuana laws should be enforced at a time when more states were legalizing pot. Prosecuting seriously ill individuals or their caregivers, it said, was "not an efficient use of federal resources."

Pennsylvania's marijuana law, officially called Act 16, allows only processed cannabis oils and tinctures. Patients cannot legally grow or smoke marijuana. New Jersey allows medical marijuana, but only the smokable variety.

Steve Auerbach, a regulated substances attorney in Montgomery County, said Congress provides some protections to patients and caregivers in more than three dozen states, but not in Pennsylvania.

A federal appropriations bill that passed last year reauthorized an amendment that prohibits the DEA from spending money to arrest patients, caregivers, and businesses that comply with their home state's medical marijuana laws.

"It doesn't say any state," Auerbach said. "It enumerates 40 states and three territories, and Pennsylvania isn't on that list."

That's because the Keystone State didn't approve its new law until several months after the federal bill was adopted.

The safe harbor provision - formally known as Section 2106 - was designed to speed access to marijuana drugs for minors with any one of 17 conditions, including autism, cancer, multiple sclerosis and epilepsy.

The provision says caregivers must obtain medical marijuana "lawfully," but no one in state government can spell out yet how that can be done.

The Pennsylvania State Police is working with the Department of Health on how to interpret the law, a spokesman said.

Attorneys at the state Attorney General's Office are continuing to review the legislation, a spokesman said.

The Department of Health, which is in charge of implementing the law, is still developing guidelines.

Spokeswoman Penny Ickes said the department expects to publish those rules this summer. She acknowledged that no state or local law could provide a legal defense to a violation of federal law.

Maria Belkadi of Mount Carmel, Northumberland County, would like to treat her autistic son's violent outbursts with medical marijuana. Belkadi said she would be willing to take her chances with the federal government but couldn't trust the state's promises to shield her from local authorities.

"Gov. Wolf can say the local D.A. won't prosecute, but I don't want to risk it," she said. "I don't want to risk ever having someone take my child from me. There's nothing in the world that's worth that."