One type of legal drug is killing far more people than heroin - and deaths just hit record numbers

In just a year, overdose deaths from opioid painkillers and heroin jumped 14%, hitting record levels in 2014, according to a new Centers for Disease Control and Prevention report released Friday.

Between 2000 and 2014, nearly half a million Americans died from overdoses involving these drugs, which research suggests act similarly in the brain.

The most commonly prescribed opioid painkillers - like oxycodone and hydrocodone - were involved in more overdose deaths than any other type of the drug. Those deaths rose by 9%.

"The increasing number of deaths from opioid overdose is alarming," CDC Director Tom Frieden said in a press release.

According to the report, two main shifts are driving the tragic trend:

• More Americans are using opiate painkillers: Research suggests that one of the reasons that abusing opiates can make people more susceptible to future heroin abuse is because the drugs act similarly in the brain. A report released in July found that people who abused opiate painkillers were 40 times as likely to abuse heroin.

• Inexpensive heroin has become more widely available: Heroin costs about one-fifth as much as most prescription opioids.

In recent surveys, nearly three in every 1,000 Americans said they used heroin in the previous year. That's up from under two per 1,000 about a decade ago, a 62% increase that translates to hundreds of thousands more people.

According to the National Institute on Drug Abuse, close to half of young people surveyed in three recent studies who have injected heroin said they had abused prescription painkillers before they started using heroin.

How does heroin affect the brain?

When someone injects, snorts, or smokes heroin, the brain converts it into morphine. Morphine binds to molecules on cells located throughout the brain and body called opioid receptors, which affect how we perceive pain and rewards.

This explains the surging sense of euphoria that many people feel when they inject the drug straight into the bloodstream. After the initial "rush," the skin gets flushed and warm, the arms and legs start to feel heavy, and thinking slows.

Because we also have opioid receptors in our brain stem - the body's main control center that is in charge of automatic processes such as blood pressure and breathing - overdosing on heroin can slow and even stop breathing, leading to brain damage or coma.