Great news via an emailed press release from the Drug Policy Alliance, not yet online that I could find:

Today, California Governor Jerry Brown signed legislation seeking to reduce the number of preventable deaths resulting from accidental drug overdoses. The passage of Assemblymember Tom Ammiano’s AB 472, the “911 Good Samaritan bill,”  received bipartisan support and makes California the tenth state in the country to take action to reduce accidental overdose fatalities by removing barriers to accessing emergency health services.

Other states with similar laws include New Mexico, Colorado, Washington, Illinois, New York, Rhode Island, Connecticut, Massachusetts and Florida. The bill was co-sponsored by the Drug Policy Alliance, California ACLU and the Health Officers Association of California. The law takes effect on January 1, 2013....

What the bill does, as summed up by the great California law blog "Around the Capitol":

This bill would provide that it shall not be a crime for any person who experiences a drug-related overdose, as defined, who, in good faith, seeks medical assistance, or any other person who, in good faith, seeks medical assistance for the person experiencing a drug-related overdose, to be under the influence of, or to possess for personal use, a controlled substance, controlled substance analog, or drug paraphernalia, under certain circumstances related to a drug-related overdose that prompted seeking medical assistance if that person does not obstruct medical or law enforcement personnel. 

For the most part, it means you can call for medical help if witnessing an overdose without fearing you'll be popped for possession, which will likely lead to more such calls for medical help, and hence save lives. (Over-the-counter naloxone, which can save those overdosing after the drugs have been consumed, would be another great policy change, as soon as people can get over thinking those who take too many drugs deserve to die.)

This policy victory had a long gestation. Brown's predecessor Arnold Schwarzenegger vetoed a bill doing the same thing back in 2010.

More from the DPA press release:

Hundreds of advocates worked to champion versions of the bill for many years. Today, they cheered the news of the passage of law.

“This is an incredibly special day for the thousands of California family members who worked so hard and for so long to pass this life-saving bill,” said Meghan Ralston, harm reduction manager of the Drug Policy Alliance. “This is just a small first step in reducing the number of fatal overdoses in California, but it’s a deeply important one.”

California is among the many states where drug overdose fatalities are the number one cause of accidental injury-related death, surpassing even motor vehicle deaths. Although studies indicate that most people overdose in the presence of others, many people either delay or do not call for emergency services. Numerous studies have shown that the number one reason that people hesitate or fail to call 911 in an overdose situation is fear of arrest for drug possession....

Overdose prevention advocates will join dozens of organizations throughout 2013 in helping to get the word out and raise awareness of the new law.

Past Reason blogging about these "good samaritan" laws.