The percentage of overdose deaths connected to natural and semisynthetic opioids such as oxycodone and hydrocodone is higher than overdose deaths connected to other types of opioids.

According to the Kaiser Family Foundation, 52 percent of the opioid overdose deaths that occurred in California in 2014 involved natural and semisynthetic opioids. Nationwide, 42 percent of such deaths involved those opioids. (Kaiser Health News, which produces California Healthline, is an editorially independent program of the foundation.)

However, the percentage of those deaths linked to heroin were higher nationwide than in California — 37 percent compared to 28 percent. The percentage of overdose deaths linked to synthetic opioids (other than methadone) such as fentanyl and tramadol was also higher nationwide than in California.

Below are definitions for the different types of opioids referenced in the data.

Natural and Semisynthetic Opioids: A category of prescription opioids that includes natural opioid analgesics (e.g. morphine and codeine) and semisynthetic opioid analgesics (e.g. drugs such as oxycodone, hydrocodone, hydromorphone and oxymorphone)

Synthetic Opioids, Other Than Methadone: A category of opioids including drugs such as tramadol and fentanyl. Synthetic opioids are commonly available by prescription. Fentanyl is legally made as a pharmaceutical drug to treat pain, or illegally made as a non-prescription drug and is increasingly used to intensify the effects (or “high”) of other drugs, such as heroin

Methadone: a synthetic opioid prescribed to treat moderate to severe pain or to reduce withdrawl symptoms in people addicted to heroin or other narcotic drugs

Heroin: an illegal opioid synthesized from morphine