[Licit and Ilicit Uses of Medicines.]

Drugs of abuse are a heterogeneous group of xenobiotics or endobiotics that alter synaptic organization in the central nervous system in a transient or permanent basis, often leading to a compulsively use. What unites its members is that they confer pleasure (hedonism) to the abusers, namely by their action in the mesolimbic dopamine system. To exert its effects, different drugs of abuse will act on receptors and neurotransmitter transporters, modeling neurotransmitter release into the synaptic cleft. Besides acting on presynapticneurons also function in neurotransmitter receptors and ion channels in postsynaptic neurons, thereby modifying the signaling pathways. In this work, the pharmacodynamic and the potential of some psychoactive substances that are typically subjected to abuse in Portugal, is reviewed. With this approach it was also possible a discussion of drugs of abuse that exhibit very different toxicological effects such as stimulants, depressants and hallucinogens. Particularly, the potential to induce dependence and addition, as well as to undergo illicit and licit uses, of central nervous system depressants, stimulants, anticholinergic antiparkinson drugs, opioids, cannabinoids and hallucinogens, is discussed.