By Peter J. PittsFor Americans under 50, the leading cause of death used to be injuries caused by accidents. But, now, the biggest killer isn't car crashes and ladder falls -- it's drug overdoses. Overdose deaths surged by 15 percent from 2015 to 2016, the largest annual increase in American history. Overdoses have pushed up death rates among all racial and ethnic groups. Policymakers and researchers are trying to make sense of this strange new reality. Some have pointed to rising rates of unemployment and disability. Others have blamed an increase in opioid prescriptions. One overlooked culprit worsening the epidemic, however, comes straight from our health care system: pharmacy benefit managers, or PBMs. To improve their bottom line, they're blocking access to prescriptions that can help prevent overdoses.For years, the federal Food and Drug Administration has encouraged the development and use of "abuse-deterrent formulations" of prescription opioids. ADFs are more difficult to physically alter -- i.e. crush for snorting or dissolve for injecting -- than traditional pills. As a result, ADFs help curb abuse and overdoses. The ADF version of OxyContin, for instance, led to a 65 percent decrease in snorting, a 56 percent decrease in smoking, and a 51 percent decrease in injection among patients with a history of abusing the drug, according to a report by the Institute for Clinical and Economic Reform. Pharmacy benefit managers, however, refuse to cover the vast majority of ADFs. Their decision impacts more than 266 million Americans insured by employers, unions, or government programs like Medicare Part D. The three biggest PBMs in the country cover no more than three of the 10 ADF opioids approved by the FDA. These pharmacies do, however, cover the cheaper, generic forms of opioids -- exactly the ones that don't have ADF properties and are readily diverted to abuse. As a result, 96 percent of all opioid products prescribed in 2015 were non-ADF, according to a new study by Tufts CSSD. No patient with legitimate medical need would pay extra out-of-pocket for an ADF opioid the patient has no intention of abusing. But would-be abusers will flock to PBMs where they can be sure they'll be able to convert pills for snorting or injection. By keeping abuse deterrent medications out of reach, PBMs essentially put out the welcome mat for abusers.PBMs say that they exclude drugs from their formularies to save patients money. But these short-term savings come with a big cost. In fact, one study found that the ADF version of Oxycontin could prevent 4,300 cases of abuse and save $300 million in medical costs over a five-year period. But PBMs aren't concerned about long-term savings. They'd rather offer cheaper drugs -- non-ADFs in the case of opioids -- and save money for themselves. The Institute for Clinical and Economic Review, a private organization that suggests drug coverage and pricing, recommended that PBMs do as much. Despite confirming the savings that ADFs could yield, ICER decided that ADFs did not provide any financial benefit. PBMs since have gladly accepted ICER's mistaken judgment. CVS Caremark, among other PBMs, claims to understand the nation's drug crisis and to be "doing everything we can to help stop it." Until they start covering all approved ADFs in their formularies, that's baloney.Pitts, a former FDA associate commissioner, is president of the Center for Medicine in the Public Interest. Follow him @PeterPitts.