LOS ANGELES — After months of debate and strong opposition, California Gov. Jerry Brown on Monday signed into a law a bill enabling doctors to prescribe drugs that will end the lives of terminally ill patients.

“This is a dark day for California and for the Brown legacy,” said Californians Against Assisted Suicide. The group warned in an Oct. 5 statement that people and families in the state could be harmed “by giving doctors the power to prescribe lethal overdoses to patients.”

With the passage of the law, California will become the fifth state allowing ill patients to end their lives. Montana, Oregon, Vermont and Washington also allow assisted suicide, while similar bills have been defeated in several states, including Colorado and Massachusetts.  

The California law, based on similar legislation in Oregon, allows doctors to give lethal drugs to adults with a terminal illness if they are deemed medically competent and expected to die within six months. It will not take effect until 90 days after the end of the legislature’s special health-care session, which will likely be next year.

The controversial bill had drawn criticism for months. It was temporarily withdrawn from the state senate in July, but resurfaced and was passed Sept. 11 by a vote of 23-14.

Local Catholic leaders had decried the measure as a violation of human dignity.

“Death will always be a mystery, and death will never be easy: for those who are dying or for those who love them. But we can make death less painful, less frightening, and we can even make it a time of beauty, mercy and reconciliation,” Los Angeles Archbishop Jose Gomez had written in a letter to state lawmakers.

“Once we start down this path — once we establish in law that some lives are not as valuable as others, not worth ‘paying for’ — there will be no turning back,” he warned. “The logic of doctor-assisted suicide does not stop with the terminally ill.”

Health care and civil-rights groups also opposed the bill, along with disabilities-rights groups, who say that the legislation discriminates against the disabled and could lead to pressure on them to end their own lives.

Opponents argued that assisted suicide sends a dangerous societal message that suicide is an acceptable way to handle pain and difficulty. They pointed to abuses in other states where the practice has been legalized and lethal prescriptions have changed hands — either knowingly or unknowingly — with deadly results.

In addition, those fighting the bill noted that terminal diagnoses are not always correct, and assisted suicide may end the life of patients who may have gone on to live longer than anticipated or lived to see medical advances that could have cured or eased their conditions.