Methadone, used in some treatment pro grams for long-term heroin users, is a drug with many of the chemical properties of heroin and many of the same effects. Unlike alcohol or the opiates, there seldom are hallucinations or thought disturbances associated with heroin use. Barbiturates are synthetically produced sedatives of which there are many varieties. They have this effect either by blocking receptor sites of excitatory synapses or by enhancing the effects of inhibitory neurotransmitters. Barbiturates also depress the cells and organs outside the central nervous system, slowing muscular responses and reducing respiration and heart rates.
Some barbiturates are addictive, producing strong withdrawal symptoms when discontinued.
All produce dependency if used with regularity. As is generally the case, once addiction develops, getting off these drugs is very difficult. End of reading passage Go to Exercises.