Substance abuse and addiction are a major global medical and social problem [101]. Most abused substances are psychoactive drugs, such as cocaine, illicit opiates (opium, morphine and heroin), amphetamine-type stimulants (amphetamine, methamphetamine, methcathinone and related substances), ecstasy-group substances (3,4-methylenedioxymethamphetamine and its analogues) and cannabinoids (a class of compounds found in cannabis, also known as marijuana or marihuana). Some licit substances, including nicotine and alcohol, are also psycho-active compounds. Psychoactive drugs are able to cross the blood-brain barrier (BBB) and act primarily on the CNS to alter brain functions, which results in changes in perception, mood, consciousness, cognition and behavior [102]. It has been estimated that the total overall costs of substance abuse in the USA alone, including health- and crime-related costs as well as loss in productivity, are more than half a trillion dollars per year [102]. The cost estimate did not fully describe the breadth of deleterious public health and safety implications, including loss of lives, family disintegration, loss of employment, failure in school, domestic violence, child abuse and other crimes. The disastrous consequences of drug abuse and addiction have made the development of antidrug medication a high priority.
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