San Francisco ? Police in a northern California town thought they had an open-and-shut case when they seized more than two pounds of marijuana from a couple’s home, even though doctors authorized the pair to use pot for medical purposes.

San Francisco police thought the same with a father and son team they suspected of abusing the state’s medical marijuana law by allegedly operating an illegal trafficking operation.

But both cases were tossed out along with many other marijuana possession cases in recent weeks because of a California Supreme Court ruling that has police, prosecutors and defense attorneys scrambling to make sense of a gray legal area: What is the maximum amount of cannabis a medical marijuana patient can possess?

No one can say for sure how many dismissals and acquittals have been prompted by the ruling, but the numbers are stacking up since the Supreme Court on Jan. 21 tossed out Patrick Kelly’s marijuana possession conviction.

The high court struck down a 7-year-old state law that imposed an 8-ounce limit on the amount of pot medical users of marijuana could possess. The court said patients are entitled to a “reasonable” amount of the drug to treat their ailments.

Law enforcement officials say the ruling has made the murky legal landscape of marijuana policy in California even more challenging to enforce.

Since California voters legalized medical marijuana in 1996, there has been tension between local law enforcement officials and federal authorities, who view marijuana as absolutely illegal.

That tension is expected to become even more pronounced if the state’s voters approve a November ballot measure legalizing possession of small amounts of marijuana.

“The way the law is now it puts law enforcement between a rock and a hard place,” said Martin J. Mayer, a lawyer who represents California State Sheriff’s Association, California Police Chief’s Association and California Peace Officers’ Association. “The measure, if it passes, will make it even more difficult. They just don’t like being in the middle.”

Prosecutors are backing away from some cases filed before the court ruling.

“Gray is not a good color for the law,” said Shasta County District Attorney Gerald Benito, who dismissed a case earlier this month and is considering dropping several more because of the ruling.

Benito cited the Supreme Court ruling in dropping charges on March 5 against James Bradley Hall, who was arrested in October and charged with growing 40 marijuana plants.

The next week, a San Francisco jury acquitted a father and son charged with growing three dozen plants. The lawyers for Thomas Chang, 62, and his son, Errol Chang, 30, based their defense on the Kelly case, arguing that the men needed that much pot to treat their medical conditions.