Research suggests that when methadone is used long-term it can build up unpredictably in the body and lead to potentially deadly slowed breathing. Used medically, approaching toxicity goes unrecognized because the pain medication effect ends long before the drug's elimination half-life. According to the USCDC, methadone was involved in 31% of opioid related deaths in the US between 1999–2010 and 40% as the sole drug involved, far higher than other opioids. Studies of long term opioids have found that adverse events may stop individuals from taking opioids long-term. In the United States in 2016, opioid overdose resulted in the death of 1.7 in 10,000 people.