With so many people in California and across the U.S. taking opioids for chronic or acute pain, it’s not surprising that opioids would factor in some car accidents. In 1993, 2% of all drivers who were to blame for a crash tested positive for opioids, but in 2016, it was 7.1%. Now, a study published in JAMA Network Open has explored the possible connections between opioid use and the initiators of fatal two-car crashes.

Turning to the Fatality Analysis Reporting System, researchers analyzed over 18,300 fatal two-car crashes and discovered that 1,467 of the drivers involved had opioids in their system. Of these, 918 initiated the crash: that is, nearly twice as many as those opioid users who did not (549). Hydrocodone was the most commonly used opioid, discovered in 32% of drivers. This was followed by morphine (27%), oxycodone (19%) and methadone (14%).

The study did not go into how opioids affect people differently. For instance, psychomotor and cognitive impairment will be less apparent in those who have been taking opioids for a while. On the other hand, those who take opioids for acute injuries will experience the full effect.

Some criticize the study for treating all forms of opioid use as the same. There are, after all, distinctions between use and abuse.

Still, even if drivers have developed a tolerance for opioids, they may still be responsible for any car accidents they caused while the drugs were in their system. Victims can find it hard to find proof against the guilty driver, so they may want to hire a lawyer before they start the process of filing a claim. The lawyer might in turn, hire crash investigators and drug experts. Victims may leave it to their lawyer to negotiate for an out-of-court settlement.