Opiates

Humans have used opiate drugs, such as morphine, for thousands of years, but these are often highly addictive and dangerous to one's health.

Humans have used opiate drugs, such as morphine, for thousands of years. Monkeys and rats readily self-administer heroin or morphine and, like humans, will become tolerant and physically dependent with unlimited access. Withdrawal symptoms range from mild, flulike discomfort to severe muscle pain, stomach cramps, diarrhea, and unpleasant mood.

Opiates increase the amount of dopamine released in the brain reward system and mimic the effects of endogenous opioids. Heroin injected into a vein reaches the brain in 15 to 20 seconds and binds to opiate receptors found in many brain regions, including the reward system. Activation of the receptors in the reward circuits causes a brief rush of intense euphoria, followed by a couple of hours of a relaxed, contented state.

Opiates create effects like those elicited by the naturally occurring opioid peptides. They relieve pain, depress breathing, cause nausea and vomiting, and stop diarrhea — important medical uses. But in large doses, heroin can make breathing shallow or stop it altogether — the cause of death in thousands of people who have died of heroin overdose.

A standard treatment for opiate addiction involves methadone, a long-acting oral opioid that helps keep craving, withdrawal, and relapse under control. Methadone helps opiate addicts rehabilitate themselves by preventing withdrawal symptoms that can motivate continued drug use. Naloxone and naltrexone are available medications that act as antagonists at opioid receptors; that is, they can curb the allure of opiates by blocking the opiate receptors so that opiates produce no pleasurable effects when they are taken. The blockers alone are sometimes useful for addicts who are highly motivated to quit. In addition, scientists are developing a long-lasting version of naltrexone that needs to be taken only once a month.

Another medication used to treat heroin addiction, buprenorphine, causes a weaker effect on the receptors than methadone and creates only a limited high, which deters an addict from abusing the medication itself. Buprenorphine has been prescribed for more than 500,000 patients in the United States.