heroin, methadone, buprenorphine
Naltrexone is a blocking agent used to treat heroin dependence. In Australia it's use is less common than methadone and buprenorphine. In high enough doses, naltrexone blocks the sites in the brain activated by heroin, so that any heroin taken will have no effect.
Naltrexone brings on a severe withdrawal reaction. Because of this, people planning to enter naltrexone treatment are often required to go through withdrawal before entering treatment. The treatment has a high drop-out rate, and appears to be best suited to highly motivated people with good social support.
The most effective treatments for heroin dependence are substitution therapies. These involve substituting other less harmful drugs for heroin, usually on a long-term basis. Doses must be high enough to prevent withdrawal symptoms.
People in treatment also need good psychological and social support, addressing motivation and coping skills, if they are to succeed in giving upheroin.
Heroin, opiates and opioids
The term opiate is used to describe naturally occurring drugs obtained from opium poppies. Opium is the resin taken from the poppies, from which the opiates morphine and codeine are extracted.
Opiates act on nerve cells in the brain called opioid receptors to depress the activity of the nervous system and act as very effective pain killers.
Heroin is not derived directly from the opium poppy—it is manufactured from morphine. It is called an opioid agonist because it activates the brain in the same way as the opiates.
Methadone is a synthetic opioid agonist that affects the brain in the same way as morphine and heroin.
While the opioid agonists activate the opioid receptors, naltrexone acts to block these receptors (so drugs like heroin cannot activate them); it is an opioid antagonist .
Buprenorphine is a mixed opioid agonist-antagonist. It activates the opioid receptors to a lesser extent than heroin, methadone and morphine, but it acts at the same time to block the receptors, preventing heroin and other opioids from having much effect.