The department sent letters to at least 30 gun owners last month, saying they had 30 days to surrender or transfer ownership of their guns.
The notices sparked backlash from residents, prompting the police review, the Honolulu Star-Advertiser reported Friday.
The letters dated Nov. 13 stated the person's ownership of firearms and ammunition was disqualified because of the use of medical marijuana.
Federal law prohibits firearm possession for unlawful users of controlled substances. Pot is classified as a controlled substance under federal law.
The names of Police Chief Susan Ballard and another police official were printed at the bottom of the letters, though only the signature of the other official was on the letter obtained by the newspaper.
A police spokeswoman said Ballard is reviewing the policy.
Dr. Clifton Otto, an advocate for medical marijuana, said the department cannot justify taking firearms away by citing medical marijuana use as a violation of federal law.
Federal scheduling of marijuana does not apply for medical use in Hawaii, he said.