Story highlights

Prescription opioids include painkillers such as morphine

Doctors prescribe them for moderate and severe pain

They produce the same effects as heroin, fueling addictions

CNN  — 

Deaths linked to opioids are skyrocketing, and so is the number of Americans abusing the drugs, experts say.

Two million Americans were dependent on prescription opioids in 2014, when the most recent data was available, federal statistics show.

Overdoses linked to opioids killed more than 28,000 people nationwide two years ago, according to the Centers for Disease Control and Prevention. The deaths include those involving heroin and prescription drugs such as oxycodone and hydrocodone.

Here are four things to know about these narcotics:

What are opioids?

Opioids are drugs that reduce pain by switching off pain receptors in the brain.

They are among the most widely prescribed drugs in the United States, the CDC says, fueling an epidemic that starts at the doctor’s office and spills onto the streets.

Doctors prescribe them so much, federal officials published national guidelines last month urging medical practitioners to be more judicious when recommending them to patients.

What drugs are considered opioids?

Prescription opioids include painkillers such as morphine, oxycodone and hydrocodone.

Others, such as the synthetic pain reliever fentanyl, are used for patients suffering from advanced terminal illness such as cancer.

Heroin is an illegal opioid derived from the same poppy plant as Food and Drug Administration-approved opioid pills. Use of heroin has skyrocketed nationwide due to a lower price and wider availability on the street.

Why are opioids dangerous?

While heroin is an