Colorado voters have approved a proposition that makes it legal to help terminally ill patients end their own life.

Colorado becomes the sixth state to have a so-called “right-to-die law,” joining Washington, Oregon, California, Vermont, and Montana. Its citizens have voted to approve Prop 106. The measure allows Colorado residents over 18 to request assistance to die if they are ill and have less than six months to live. They must also be judged competent enough to make their own choice and must voluntarily ask for the medicine that would kill them. Before, helping someone end their life was a crime.

Assisted suicide — sometimes called physician-assisted suicide or “death with dignity” — has become an increasing public health issue as it is legalized in more states. Supporters say it respects patients’ autonomy by allowing them to control their lives until the very end and die on their own terms. In many cases, supporters say, it could relieve physical suffering that would only continue to worsen.

Opponents argue, often on religious grounds, that helping take a life in any situation is ethically wrong. Disability activists have also criticized some of the language surrounding the debate. For example, they claim that comments supporting the right-to-die because “life isn’t worth living if you’re disabled” are discriminatory. There are also concerns that legalizing assisted suicide would lead to a “slippery slope” situation where people become too quick to use the option, or the guidelines for who can request assisted suicide become more and more lax.

Former NPR host Diane Rehm — whose husband starved himself to death because assisted suicide is a crime in Maryland — has been a high-profile advocate. The assisted death of 29-year-old Brittany Maynard in Oregon two years ago also brought a lot of attention to the cause. (The Colorado proposition is modeled in part after Oregon’s.) The procedure has been approved in several European countries, including Belgium, where the first minor was euthanized in September, and the Netherlands, where requests have doubled in the past five years.

Here in the US, there are no federal laws on the matter, so individual states are passing their own legislation. But with Colorado decriminalizing euthanasia and other states possibly following suit, it may only be a matter of time before there is growing pressure to address this issue at the federal level.