The actress, 44, was released on bail after surrendering to Loudoun County Sheriff's Office in Virginia on Tuesday.
Police say the items allegedly tested positive for narcotics.
The Class 5 felony charge stems from a police investigation of the actress' personal belongings left behind on a United flight arriving at Washington Dulles International Airport on January 20.
McGowan has been one of the leading voices against sexual harassment in Hollywood.
McGowan, however, claimed that the warrant was a conspiracy.
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McGowan later accused Weinstein of rape.
Ms McGowan reportedly reached a settlement with Weinstein after a hotel room encounter during the Sundance Film Festival.
After apparently learning about the charge last month, McGowan, whose name has hit the headlines with the onslaught on Weinstein coverage, tweeted: "Are they trying to silence me?"
He faces police investigations in Los Angeles, New York and London and has been sacked from The Weinstein Company, the studio he co-founded with his brother.
A warrant was issued for the actress' arrest for felony possession of a controlled substance. More than 80 women have come forward with allegations of sexual harassment and assault.