All products that can trigger dependence in humans have a property in common: they increase the amount of dopamine available in an area of the brain called reward circuit, whose role is to participate in the modulation of pleasure.
This circuit is involved in the reward (feeling of well-being and pleasure) provided by the behavior related to the nutrition and reproduction of the species. He thus participates in the satisfaction of living. Psychoactive substances abnormally stimulate this natural circuit and generate, eventually, the possibility of a more or less permanent imbalance.
The potential toxicity of psychoactive substances, like any drug, is related to the amount consumed and varies from one product to another. So, the more we consume a product at toxic doses, the more we suffer the consequences. Conversely, the less we consume a product, or if we consume it in non-toxic doses, the less we suffer the harmful consequences.
A psychoactive substance whose molecular structure resembles that of a substance naturally produced by the body, such as dopamine or serotonin, can bind in place of this substance on specific brain receptors, thus producing characteristic effects.