At Saturday's Democratic presidential debate, Hillary Clinton mentioned a little-known drug when asked about America's opioid painkiller and heroin epidemic: naloxone.

The drug — also known by its brand name, Narcan — is at the center of America's new public health approach toward drugs, a shift from the old war on drugs. As the country deals with an opioid painkiller and heroin epidemic that's pushed drug overdose deaths above car crash and gun violence deaths, policymakers are increasingly looking for more effective ways to cut down on drug use and prevent deadly overdoses. And naloxone speaks to that shift.

Naloxone is a simple drug: It can reverse the effects of an overdose caused by heroin or opioid painkiller use. But until a few years ago, states tended to have strict laws around it — requiring a doctor's prescription that could put it out of reach for many opioid users and their families and friends.

But in recent years, states have loosened their laws around naloxone. Sometimes the legal changes fundamentally alter the relationship between the criminal justice system and drug users: Whereas a police officer may have locked up an addict for possessing heroin before, that same cop may now find himself saving the life of that addict by administering naloxone to reverse a deadly overdose. The cop's role is quite literally going from potentially ruining a drug user's life to actually saving it.

Naloxone, then, demonstrates just how much America is changing its approach to drugs. But to understand why, it's important to first understand the drug, what it does, and the policies surrounding it.

Naloxone can save opioid users from overdoses

Naloxone, short for naloxone hydrochloride, temporarily reverses the effects of opioids like heroin and prescription painkillers like OxyContin and Percocet. So it reverses all the positive effects, including the painkilling benefits. But it also reverses all the negative effects, such as a deadly overdose.

"Unlike something like alcohol, which is complicated and goes everywhere water does, opioids are really simple," Keith Humphreys, a drug policy expert at Stanford University, said. "They bind to a receptor in the brain, so you know exactly where they are. The naloxone goes to that same receptor, forces the opioids out of the receptor, and binds to the receptor itself."

Naloxone's effect lasts 30 minutes to an hour, which is usually enough to stave off an overdose that could turn deadly and, if necessary, get someone into other lifesaving care. If the effect doesn't last long enough, naloxone can be reapplied, which is done through an injection or nasal spray.

Naloxone rarely has major side effects, but it can cause mild symptoms such as dizziness, tiredness, weakness, nervousness, and diarrhea. It can also send some addicts into sudden withdrawal, which can cause them to become violent — but still a much better outcome than death. Despite this, states used to impose big restrictions on accessing naloxone.

More states are letting first responders — and even family members — access naloxone

Over the past several years, states have taken more and more steps to relax the laws surrounding naloxone. Under normal circumstances, naloxone would be a prescription drug that only doctors can prescribe. But states have taken several kinds of measures to expand its availability, as outlined by Corey Davis, deputy director of the Network for Public Health Law, as of June 2015:

Third-party prescriptions : In 38 states, individuals can ask doctors to prescribe naloxone to other people who are at risk of an overdose. For example, a brother might ask for a naloxone prescription so he can give it to his sister who's addicted to heroin.

In 38 states, individuals can ask doctors to prescribe naloxone to other people who are at risk of an overdose. For example, a brother might ask for a naloxone prescription so he can give it to his sister who's addicted to heroin. Prescribing by standing order : In 28 states, groups can distribute naloxone to others under specific criteria. For example, a public health agency could distribute the drug to people who attend an overdose rescue training program that teaches them how to apply the drug to someone who is overdosing.

In 28 states, groups can distribute naloxone to others under specific criteria. For example, a public health agency could distribute the drug to people who attend an overdose rescue training program that teaches them how to apply the drug to someone who is overdosing. Equipping first responders with naloxone : In many states, first responders like police and firefighters carry naloxone, so they can administer it to people when they first respond to a 911 call. Since an overdose can turn deadly or cause brain damage quite quickly, the minutes saved from not having to wait for an ambulance can literally save lives.

In many states, first responders like police and firefighters carry naloxone, so they can administer it to people when they first respond to a 911 call. Since an overdose can turn deadly or cause brain damage quite quickly, the minutes saved from not having to wait for an ambulance can literally save lives. Pharmacy availability: In a handful of states, people can go to pharmacies and ask for naloxone at the counter. The pharmacist will then go through some procedures, but generally this lets people buy naloxone quite easily for themselves or others.

Combined with this increased access, states have also passed laws that limit someone's legal liability for administering naloxone under good intentions. The idea is that people shouldn't be afraid of the legal consequences if they were to make a wrong call and administer naloxone to someone who appears to be dying from an overdose but actually isn't, or injure someone in the process of applying naloxone. As Humphreys wrote in a Health Affairs paper, this fear is likely overstated since naloxone's side effects are mild and rare — but it's a relatively simple legal change that can increase someone's willingness to administer naloxone.

Still, that doesn't mean naloxone is easily available to everyone. Distributing naloxone and training people how to use it can be costly. Although the Obama administration has unlocked some funding for naloxone programs, it's still out of reach for many poorer, rural communities — those that may be hit hardest by the opioid epidemic.

But overall, states have increased access to naloxone in the past several years — with the explicit goal of saving lives.

There is a risk to naloxone, but it's nothing compared with the huge public health benefits

Although naloxone can and has saved lives by reversing otherwise deadly overdoses, it's not without any risks. One of the dangers, pushed particularly hard by the Bush administration, is that it might make addicts feel like they can safely use opioids — and that would lead to greater rates of drug use and abuse. But drug policy experts, public health officials, and the Obama administration now largely agree that this fear is overblown — because the benefits of naloxone are simply too large for theoretical downsides to overcome.

"It's not that people don't do any risk compensation," Humphreys, who served as an adviser for the Obama administration, said. "It's just that the risk compensation is very often swamped by the benefits."

Humphreys cited the example of safety devices like seat belts. The empirical literature suggests seat belts do make people drive a little faster, but that's overcome in droves by the many safety benefits that seat belts provide — by, for example, reducing the deadliness of car crashes.

Similarly, naloxone may make people more likely to think they can get away with recreationally using painkillers or heroin, but that tiny increase in use is relatively small compared with the benefits of saving someone's life. "Maybe there's a high school kid out there who would experiment with heroin who wouldn't otherwise," Humphreys said, "but then there's 10 other kids experimenting who would be dead but are alive."

"Maybe there's a high school kid out there who would experiment with heroin who wouldn't otherwise, but then there's 10 other kids experimenting who would be dead but are alive"

Naloxone also might make someone feel like she doesn't need to check into treatment for drug abuse, because the risk of overdose is diminished. This is wrongheaded: Even if someone survives multiple drug overdoses thanks to naloxone, it's entirely possible that an overdose will eventually come along in which naloxone isn't available, isn't administered correctly, or is administered too slowly to prevent serious brain damage. In this kind of scenario, naloxone might extend someone's life — but it wouldn't solve the addiction at the root of the problem and permanently prevent the worst effects.

Still, the alternative in many cases is that someone simply dies, and dead people can't get treated for drug abuse. So naloxone could, in theory, enable people to get care — by letting them live through a horrible, near-death situation to show them just how dangerous what they're doing is. (The idea of "hitting rock bottom" is big in addiction treatment: Some addicts seemingly need to get to a really bad point where they desperately feel like they need to stop using drugs before they actually do.)

"It's a teachable moment," Humphreys said. "It gives you a chance to hook them in."

One study in Massachusetts also found that communities with higher rates of training for a naloxone program had larger reductions in opioid overdose death rates than those with no enrollment. This research only established correlation, so it's possible something else happened in these communities that drove down deaths. But public health experts by and large expect naloxone to play a role in cutting down on deadly overdoses, although there hasn't been a lot of good research into the drug's societal and public health effects just yet.

So the benefits appear to greatly outweigh the risks. But the risks also emphasize why it's important to connect policies that open access to naloxone with policies that increase the availability of drug treatments. Otherwise, lawmakers risk addressing an effect of more opioid use — more overdoses and the damage they cause — without ever really getting at the underlying, life-threatening cause.