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is generally defined as the use of a drug with such frequency that the user has physical or mental harm or it impairs social abilities. The substances that are discussed in this report are called psychoactive drugs; those drugs that influence or alter the working ....

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.... a neurotransmitter. One major neurotransmitter is called dopamine, which is involved in feelings of pleasure. When the drug is released into the brain, it blocks the dopamine from returning to the first brain cell. Repeated use changes the brain cells so that normal messages can't be sent between brain cells. The drug must always be present in order for neurotransmissions to take place. The user is only able to feel pleasure from the cocaine rather than the things he/she used to find pleasurable. This is called drug addiction or dependence. Drug Classification Drugs are generally categorized into two groups, stimulants and depressants. ....