These PET scans show the normal distribution of opioid receptors in the human brain. A new study suggests ketamine may activate these receptors, raising concern it could be addictive. Philippe Psaila/Science Source hide caption

A police officer speaks to a man on New Haven Green, where more than 70 people fell ill from suspected drug overdoses on Wednesday in New Haven, Conn. Bill Sikes/AP hide caption

Bea and Doug Duncan outside their home in Natick, Mass. The coaching they got from the Community Reinforcement and Family Training program, they say, gave them tools to help their son Jeff stick to his recovery from drug use. He's 28 now and has been sober for nine years. Robin Lubbbock/WBUR hide caption

Opioid prescriptions went down among doctors informed of patients' overdose deaths. WILL & DENI MCINTYRE/Getty Images hide caption

A homeless man in Denver draws heroin into a syringe. Treatment centers in the city say patterns of drug use seem to be changing. While most users once relied on a single drug — typically painkillers or heroin or cocaine — an increasing number now also use meth. Andy Cross/Denver Post via Getty Images hide caption

A drug user prepares a hit of heroin inside VANDU's supervised injection room. Rafal Gerszak for NPR hide caption

Prescription opioids like OxyContin flooded Missouri during the past six years. Photo Researchers/Science Source hide caption

At safe injection sites like Insite, in Vancouver, Canada, drug users can inject drugs under the watch of trained medical staff who will help in case of overdose. Elana Gordon/WHYY hide caption

Shannon Hubbard has complex regional pain syndrome and considers herself lucky that her doctor hasn't cut back her pain prescription dosage. Will Stone/KJZZ hide caption

Any amount of opioid use was associated with a higher risk of arrest, parole or probation according to a new study. Marie Hickman/Getty Images hide caption

Marketing payments to doctors by makers of opioids have declined. Wallace Garrison/Getty Images hide caption

In 2016, Donald Trump captured 68 percent of the vote in West Virginia, a state hit hard by opioid overdoses. BRENDAN SMIALOWSKI/AFP/Getty Images hide caption

Main Street in McArthur in Vinton County, Ohio. Though the opioid crisis endures in Ohio, the problem is now compounded by the resurgence of methamphetamine addiction. Arezou Rezvani/NPR hide caption

Policymakers in Illinois and other states want to make it easier to get medical marijuana for pain relief. LPETTET/Getty Images hide caption

A pharmacist holds a bottle of OxyContin earlier this year at Daniel's Pharmacy in San Francisco. Jeff Chiu/AP hide caption