Opiates stimulates the pleasure centers in key areas of the brain. This system involves neurons in the midbrain that use the neurotransmitter called "dopamine." These midbrain dopamine neurons project to another structure called the nucleus accumbens which then projects to the cerebral cortex. This system is responsible for the pleasurable effects of some opiates and for the addictive power of the drug. Interestingly, researchers have found that although opiates and nicotine are very different substances, the end result as far as dopamine signaling is very much the same.
Opioid receptors and endorphins in the brain also interact with the neurotransmitters dopamine and noradrenaline which have long been implicated in depression. It is thought therefore that a deficiency of endorphins may also be involved in depression and that they and agents that mimic them, may be a useful treatment. This excessive release of dopamine and stimulation of the reward system can lead to addiction. Opiate addiction often develops gradually and many victims are unaware that they are in need of treatment until they are highly dependent on opiates.
Opiates such a heroin that taken intravenously often induce emesis. The explanation for this may be that the area of the brain responsible for mediating opioid-induced emesis has a permeable blood-brain barrier. Activities that release endorphins are usually habit-forming (we rarely call them addictive). These include cracking knuckles, strenuous exercise, and orgasm. Detox medications used in the treatment of opiate addiction have the potential for abuse because they are classified as opiate and can produce sensations of euphoria, analgesia and sedation like other opiates, though to a lesser degree. The medications also don’t impair cognitive or motor skills like their addictive counterparts, and work by blocking the effects of more potent opiates on brain receptors, thus disabling the user’s ability to get high.
Semi-synthetic opiates are created from naturally occurring opioids and include buprenorphine, hydrocodone, oxycodone, hydromorphone and oxymorphone. Due to their pain relieving properties, opiates and sythentic opiates are the most often prescribed type of prescription drugs.Powerful opiates such as heroine, morphine, and opium produce an intense euphoria, or rush, that lasts only briefly and is followed by a few hours of a relaxed, contented state. Opiates activate pathways in the brain that block pain and create euphoria. Sudden withdrawal by heavily dependent users who are in poor health is occasionally fatal, although heroin withdrawal is considered much less dangerous than alcohol or barbiturate withdrawal.