Drugs alter normal levels of chemicals involved in the sensations of pleasure

All drugs of abuse, including alcohol, activate a system in the brain that communicates “This is important! — Pay Attention!” sometimes also referred to as the “reward pathway.” This system has to do with communicating reward and makes eating, exercising and procreating enjoyable.
The same system also communicates a sense of urgency to address unwanted situations such as pain or anxiety in such a way as to promote physical well-being. Drugs and alcohol activate these same systems but there is no corresponding survival situation.
How drugs accomplish this varies: They may masquerade as natural neurotransmitters – directly causing an effect; they may block chemicals that would normally limit neuronal activity – increasing the effect; they may enhance chemicals that in turn increase release of “pleasure” neurotransmitters – greatly increasing activity; or block chemicals that normally remove these neurotransmitters from their site of activity – prolonging their effect.
Addictive drugs are thought to exert their effects by influencing dopamine directly or indirectly: By altering other neurotransmitters that modulate dopamine levels such as GABA (gamma-aminobutyric acid – a neurotransmitter whose deficiency is linked to anxiety, irritability, insomnia and depression), endogenous opioids, serotonin, acetylcholine and noradrenalin.61;62 Whether direct or indirect, the resulting unnaturally high levels of the neurotransmitter dopamine then modulates other neurotransmitters.63 These biochemical complexities are one reason why substitute drugs have failed more often than not to offer a solution.
While the person is feeling “pleasure” brain chemistry is being compromised in long-lasting ways. Normally, once the novelty of a situation is gone the corresponding chemical systems stop communicating; after one eats, hunger and cravings cease. But the drug-induced message does not share a reality with the abuser’s environment; instead becoming reinforced by taking more drug. Eventually, the addicted person’s chemical communication system indicates that “all is well” when the drugs or alcohol are present. When the drugs or alcohol leave the addict’s system, the brain and body perceive the deficit.
Continued use of the drug ultimately depletes these neurotransmitters, while the cells on the receiving end reduce their numbers of active receptors. Recovery from addiction requires adequate supplies of neurotransmitter precursors, vitamins and minerals essential to restoration.64;65

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