LIKE ENDORPHINS: Opioid painkillers such as OxyContin, vicodin, dilaudid, percocet or methadone work by blocking the neuroreceptors in the brain and spinal cord that transmit pain signals, in much the same way that naturally occurring endorphins do. In the absence of pain, the chemicals in painkillers can produce a feeling of euphoria.

A MORE INTENSE EUPHORIA: Heroin acts on the same receptors as prescription painkillers but gives a more intense euphoria. It also creates a more intense dependence. With prolonged use, the body’s natural levels of chemicals related to pleasure drop off, leaving a user with a dependence on opiates to maintain a normal level of contentment. The dependence grows with continued use, until a person becomes physically ill without opiates.

SLOWING RESPIRATION: Opiates slow down the body’s respiratory system. If too much is taken, or mixed with other respiratory depressants such as alcohol, breathing can slow down so much that the heart and brain don’t get enough oxygen, causing death.

TREATMENT MEDICATIONS: Addiction treatment medicines like methadone and buprenorphine, also known as suboxone, block the same neuroreceptors but without inducing the same level of euphoria and without increasing tolerance to the medicines so the dosage does not have to increase.

IN TANDEM WITH THERAPY: Drug-replacement therapy, such as methadone and buprenorphine, is meant to be part of treatment that includes either inpatient therapy at a residential facility or outpatient therapy.

HOW HEROIN IS USED: Many first-time users snort heroin, which is absorbed into the bloodstream through the capillaries in the nose. Injecting it directly into a vein offers a more efficient and intense delivery of the drug.

NO QUALITY CONTROLS: Unlike prescription pain pills, heroin has no quality controls. Purity is often as low as 5 percent or as high as 25 percent. It can contain methamphetamines or the powerful painkiller fentanyl as well as other substances. Heroin laced with fentanyl has been linked to several overdose deaths in the Northeast.