Gerald Hough

A drug is a substance that on entering the body changes the body or its functioning

Drugs fall into one of two general classes,

agonist mimics or enhances the effect of a neurotransmitter.

by increasing the transmitter’s effect on the receptor, or by blocking the reuptake or the degradation of the transmitter. An antagonist may occupy the receptors without activating them, simultaneously blocking the transmitter from binding to the receptors. Or it may decrease the availability of the neurotransmitter, for example, by reducing its production or its release from the presynaptic terminals.

Psychoactive drugs are those that have psychological effects, such as anxiety relief or hallucinations.

Many abused drugs also produce withdrawal reactions. Withdrawal is a negative reaction that occurs when drug use is stopped. Withdrawal symptoms are due at least in part to the nervous system’s having adapted to the drug’s effects, so they are typically the opposite of the effects the drug produces. For example, the relaxation, constipation, chills, and positive mood of heroin are replaced by agitation, diarrhea, fever, and depression during withdrawal.

Regular use of most abused drugs results in tolerance, which means that the individual becomes less responsive to the drug and requires increasing amounts of the drug to produce the same results.

tolerance results from compensatory adaptation in the nervous system, mostly a reduction in receptor number or sensitivity. Tolerance is one reason for overdose, because tolerance can develop in response to the drug’s pleasurable effects without developing in response

The opiates are drugs derived from the opium poppy (

They are analgesic (pain relieving) and hypnotic (sleep inducing, which is where it gets its scientific name), and they produce a strong euphoria (sense of happiness or ecstasy). Their downside is their addictive potential due to the euphoria.