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Summary: Psychoactive Drugs

Psychoactive drugs are those that affect states of consciousness. They come in several varieties: stimulants, which increase activity, depressants, which reduce activity, opiates, which reduce pain and produce a numb feeling; hallucinogens, which produce a state resembling a waking dream; and hypnotics, which produce a feeling of altered perception and thought without the dramatic changes of hallucinogens.

The most commonly used drug is alcohol. Researchers describe the characteristic mental state produced by alcohol as "alcohol myopia." Attention to long-term plans and problems is reduced, while attention to immediate events and stimulation is increased.

Stimulant drugs include amphetamines, cocaine, and caffeine. Cocaine can cause sudden heart attacks because it reduces activity in the vagus nerve, which normally lowers the heart rate as blood pressure rises. Behaviorally, both cocaine and methamphetamine mimick the natural effects of stress.

Opiates are drugs such as heroin and morphine, similar to the endorphins, natural pain-killing drugs in the body. Nitrous oxide, a gas used as an anesthetic by some dentists, produces cross-tolerance to opiates and therefore must involve similar neural mechanisms.

Marijuana does not fit easily into other drug classifications. Its chemical action is unique, affecting mostly the cerebral cortex and hippocampus of the brain. Chemicals that block cannabanoid receptors may prove useful as anti-obesity drugs.

Psychedelics such as LSD produce dramatic, dream-like experiences while awake. MDMA (ecstasy) has become a popular recreational drug. Users often report that it makes them feel like they "love everybody." MDMA has a dose/toxicity ratio less dangerous than that of alcohol, when toxicity is defined as death. However, animal experiments suggest that MDMA may be neurotoxic (neuron-killing) at three times the minimal psychoactive dose.

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