Abstract
There are many drugs used to treat various diseases. Of course, all the drugs are supposed to be beneficial but many have certain side effects. The drugs may accumulate in various tissues and result in the serious side effects immediately or later after few years. The short- and long-term effects of drug abuse may vary from person to person. Many people currently suffer from the side effects of abusing drugs every day. The factors affecting the exact symptoms that are experienced may depend on a person's age, gender, individual physiology, genetic makeup, and mental health condition. The abnormal behavioral manifestations that occur during addiction have been viewed by many as “choices” of the addicted individual, but recent imaging studies have revealed an underlying disruption to brain regions that are important for the normal processes of motivation, reward, and inhibitory control in addicted individuals. Hence, drugs addiction causes dysfunction of brain tissue. Besides, drugs addiction affects gene expression, protein products, and neuronal circuits. Future research might allow us to clarify whether this is the reason that youths seem to become addicted to nicotine and alcohol. Drugs of abuse increase extracellular dopamine concentrations in limbic regions, including the nucleus accumbens (NAc) Other drugs, such as nicotine, alcohol, opiates, and marijuana,work indirectly by stimulating neurons (GABA-mediated or glutamatergic) that modulate dopamine cell firing through their effects on nicotine, GABA, mu opiate, or cannabinoid CB1 receptors, respectively. It seems that increases in dopamine are the prediction of reward and for salience. Salience refers to stimuli or environmental changes that are arousing or that elicit an attentional-behavioral switch.