California is officially fifth American state where physician-assisted suicide is legal.

The state's new law, which Gov. Jerry Brown signed last October, takes effect today. California doctors can now prescribe lethal medications to terminal patients with less than six months left to live. The bill gained momentum this year after the death of Brittany Maynard, a 29-year-old woman with brain cancer who moved to Oregon to take advantage of the state's death-with-dignity law.

California follows Oregon, Washington, Vermont, and New Hampshire in legalizing aid in dying. About one in six Americans — 51 million people — now live in a state where it is legal for doctors to prescribe medications to terminally ill patients that will end their lives.

None of the laws, so far, are used by many patients, and they work differently from how many imagine assisted suicide to be. Here are five important facts about how aid-in-dying laws work — and what such a provision now means for California.

1) Aid in dying requires patients to take their own lives

Discussions of end-of-life care often conjure images of a Dr. Kevorkian figure who administers a lethal dose of medication to a patient. But the aid-in-dying laws currently on the books work differently. Doctors do not administer a lethal injection; what Kevorkian did would be illegal under the California proposal.

Existing aid-in-dying laws give doctors the authority to write a prescription for deadly sedatives. These can be prescribed to a terminally ill patient who is deemed capable (by a health professional) to make decisions about his or her own treatment.

Under the California law, patients will have to make an oral request for the medications twice and 15 days apart. The patient will also submit a written request will and need two doctors — both the primary physician and a "consulting physician" — to approve the request.

Since 1997, Oregon estimates that a total of 752 patients have died with the aid of lethal prescriptions

The law specifically notes that providers cannot administer the drugs themselves, and that such an action is "unprofessional conduct."

"If a doctor is allowed to give a patient a lethal injection, the doctor is the last actor," says Alan Meisel, a bioethicist at the University of Pittsburgh who has written extensively on right-to-die laws. "In Oregon and Washington, the patient is the last actor. And that lets them reserve the right not to act at all."

2) Five states have aid-in-dying laws

On October 27, 1997, Oregon became the first state to allow physicians to prescribe lethal medications to terminally ill patients. Physicians who wrote these prescriptions would not be allowed to administer the deadly drugs but could prescribe them to a consenting adult with less than six months left to live.

Washington followed with the nation's second assisted suicide law in 2008, and Vermont came after in 2013. There is also one state, New Mexico, where the court system has found a legal right to assisted suicide. That case involved two doctors who sought to prescribe fatal drugs to a 49-year-old cancer patient in Albuquerque. The Second District judge writing the opinion wrote, "This court cannot envision a right more fundamental ... than the right of a competent, terminally ill patient to choose aid in dying."

3) Few patients seek and are granted aid in dying

Oregon has the longest-standing aid-in-dying law, and has published data every year on how the law works. The releases include information on how many people fill prescriptions for lethal medications and how many patients ultimately ingest those drugs.

Since 1997, Oregon estimates that a total of 752 patients have died with the aid of these lethal prescriptions, including 72 last year. That accounts for about 0.2 percent of all deaths in Oregon last year. To put it another way: For every 10,000 Oregonians who died in 2013, about 22 of them did so with aid-in-dying prescriptions.

One New England Journal of Medicine study has found that Oregon doctors deny the vast majority of requests received for lethal prescriptions, accepting about one in six. Patients who had symptoms of depression or who viewed themselves as a burden were less likely to receive a requested prescription.

4) One-third of those who seek aid in dying don't ultimately use the drugs

This is perhaps one of the more surprising things Oregon has learned with its aid-in-dying law: One in three patients who obtain lethal medications don't end up using the prescription. Through 2013, the state has filled 1,173 aid-in-dying prescriptions, but only 752 of those have been used.

It's possible that some of the more recently filled prescriptions will be taken at some point in the near future and the ratio of those who use the drugs will increase. But there's a clear pattern of some terminally ill patients filling these prescriptions but never using them.

"A lot of people view this as buying an insurance policy against a miserable death"

"What this tells us is a lot of people view this as buying an insurance policy against a miserable death," Meisel, the University of Pittsburgh bioethicist, says.

This is similar to how Brittany Maynard described her experience, in a series of videos released last year. She ultimately did follow through on a publicly announced plan to take the medication on November 1. But two days prior, she released a video saying it was possible she would delay, depending on the state of her health.

"If November 2 comes along and I'm still alive, I know that we'll just still be moving forward as a family, out of love for each other, and that the decision will come later," Maynard said in that video.

5) Aid-in-dying patients are more likely to be affluent and well-educated

When Oregon was debating its aid-in-dying law, opponents worried that doctors might use it to target lower-income patients who would have trouble paying medical bills. It would be less expensive for those people to die than to continue receiving treatments they might never be able to afford.

Oregon has monitored certain characteristics of those who seek aid-in-dying prescriptions, and they find the opposite has happened. It's the more affluent Oregonians, many of whom are likely more informed about their options in battling a terminal illness, who seek out the lethal drugs.

More than half (53.5 percent) have at least a bachelor's degree. Nearly all (96.7 percent) have some form of health insurance.

6) Nearly all aid-in-dying patients are using some form of hospice care

The Oregon data suggests that aid in dying is a complement to hospice care, which aims to make patients comfortable in battling terminal illness, rather than a replacement. In 2013, more than 85 percent of those who used the aid-in-dying law were enrolled in hospice care at the time of death. One poll has found that residents of states with aid-in-dying laws have higher awareness of hospice options than the general public.

7) Physicians help people die in California already

Of course, there are already terminally ill people who live in California right now, with no aid-in-dying policy at all. This means that some doctors, largely oncologists, almost certainly end up participating in different versions of assisted suicide. One 2000 survey of more than 3,000 oncologists found that more than 10 percent said they had, at some point in their career, assisted with a patient's suicide.

The real number might be much higher. Most doctors don't like talking about physician-assisted suicide because they work in states where it is technically illegal. "People don't want to admit to it," says Meisel. "We've got no good data, and everything we know is conducted by anonymous questionnaire."

There are legal ways for doctors to help patients end their lives. Assisting patients in ending eating or drinking, for example, is one way to guarantee death. But that can be a painful end. Patients can become delirious with thirst. If they ask for water, should a doctor chalk it up to delirium and continue denying hydration or cede to the patient's demands?

"The patient may change her mind and say, 'Give me water, give me ice,'" Meisel says. "And then what are you supposed to do?"

Those questions underpin the case that Maynard made for death with dignity — she knew what a natural death from her brain cancer would be like. "My glioblastoma is going to kill me, and that's out of my control," Maynard told People. "I've discussed with many experts how I would die from it, and it's a terrible, terrible way to die."

This is the kind of death that, by moving to Oregon, she avoided. And it's the kind of death that the new California law will likely prevent for others.