America is in the middle of an opioid painkiller and heroin epidemic. The rise in opioid painkiller and heroin abuse over the past several years — and the overdose deaths that resulted from that abuse — have elevated drug overdose deaths beyond gun violence deaths and car crash deaths. The situation has gotten so bad in New Hampshire in particular that it is now the top issue for voters in the state, which will be the first to vote in the presidential primary elections.

As a result, the opioid epidemic has slowly garnered more attention from presidential candidates. New Jersey Gov. Chris Christie spoke about treating addicts through public health, not criminal justice, policies on the campaign trail. Hillary Clinton released a $10 billion plan that deals with drug abuse as a primarily public health issue. And now, Carson finally brought the issue to the debate stage after it went nearly unmentioned for one Democratic debate and three Republican debates.

But the opioid painkiller and heroin crisis has some complicated beginnings. Here's a brief breakdown of the epidemic, how it began, why it got so bad, and what government officials are doing about it.

1) More people now die from drug overdoses than from car crashes and gun violence

No chart puts the epidemic's horror in perspective better than this: Drug overdoses, more than half of which are linked to opioid painkillers or heroin, now kill more people than car crashes and gun violence. Drug overdoses even kill more people than AIDS did at the height of the HIV/AIDS epidemic in the 1990s. This is a big public health crisis, which shows why leading presidential candidates are treating it that way.

2) In 2012, doctors prescribed enough opioid painkillers to give a bottle of pills to every adult in the country

Since the 1990s, there's been much more attention on the US's chronic pain problem — a 2011 report from the Institute of Medicine found that about 100 million US adults suffer from chronic pain. This led pharmaceutical companies, the federal government, and patient advocacy groups — some of which get a lot of money from drug companies — to push doctors to prescribe more and more opioid painkillers. The drugs proliferated as a result, and now there are enough prescriptions for opioid painkillers to give a bottle of pills to every adult in the US.

But these pro-painkiller campaigns were built largely on deception. Pharmaceutical companies — including Purdue Pharma, which would later pay hundreds of millions in fines for its marketing — claimed that opioid painkillers weren't more addictive and harmful than other drugs. But we've always known that's false: Opioids are extremely addictive, and they carry a high risk of overdose, especially among longer-term users.

3) Prescription painkiller overdose deaths leveled out for a few years, but heroin overdose deaths are on the rise

The proliferation of opioid painkillers and overdose deaths led local, state, and federal agencies to crack down on the drugs — particularly on "pill mills" that carelessly handed out painkillers. The crackdown made the drugs less accessible and seemed to level out the number of painkiller deaths for a few years. But it had a negative side effect: It led opioid addicts to turn to another opioid — heroin — for their fix. The result, as the chart above shows, is that heroin overdose deaths have more than tripled since 2010.

That doesn't mean cracking down on painkillers was a mistake. The crackdown appeared to slow the rising number of painkiller deaths, and may have prevented doctors from prescribing the drugs to new generations of potential addicts. So the crackdown did lead to more heroin deaths, but it will hopefully prevent future populations of drug abusers, which could have suffered even more overdose deaths. That's why government agencies came down on painkillers, even though they knew it could lead to a temporary spike in heroin use.

4) The price of heroin is at historic lows

One of the reasons opioid painkiller addicts turned to heroin is because it's actually much cheaper and more accessible than street-purchased painkillers. As the chart above shows, heroin's price as of 2007 was at historic lows after falling for decades.

But heroin's low price also shows why the opioid epidemic is being largely treated more as a public health issue than previous drug crises. The chief goal of the war on drugs is to go after drug supplies to bring up the price of drugs and make them less affordable to users and abusers. This has clearly failed, based on heroin's price data. So drug policy experts — and many local, state, and federal officials — now want a public health approach that focuses more on treating drug abusers and potentially less on going after drug dealers and traffickers.

5) Most people who meet the definition for a drug abuse disorder don't get treatment

A greater focus on the public health side of drug addiction is desperately needed. According to 2014 federal data, at least 89 percent of people who meet the definition for a drug abuse disorder don't get treatment. And that's likely an underestimate: Federal household surveys leave out incarcerated and homeless individuals, who are more likely to have serious, untreated drug problems.

There are lots of explanations for the low rates of treatment, including stigma against drug addicts. But one reason is there simply aren't enough treatment facilities: During President Barack Obama's visit to West Virginia, several families told the president that they had to send their sons and daughters to other states for treatment or wait up to three months for care. To put this in perspective, imagine if you had to wait three months to get a family member into care for a life-threatening illness. With the rising number of drug overdose deaths, this long wait period is increasingly seen as unacceptable — and is leading to a more robust government response.