A psychoactive substance (PAS) is a natural or synthetic product that modifies mainly the functioning of the central nervous system. It alters the functions of the brain and can cause changes in perception, sensations, mood, consciousness and other psychological and behavioural functions. There are three main classes of PASs: stimulants, which accelerate the body’s normal processes (cocaine, amphetamines, coffee, tobacco, energy drinks, etc.), disruptors or hallucinogens, which alter perception and judgment (cannabis, LSD, etc.) and depressants, which cause a feeling of relaxation and a loss of inhibitions (alcohol, several drugs, including tranquillizers, hypnotics, analgesics, etc.). PASs can be legal (off-the-shelf or by prescription) or illegal.
Although the dividing line between use and misuse can sometimes be unclear, when the behaviour of a person using PASs becomes dangerous for others or themself, causing significant decline or clinically evident distress, this person can be said to have a substance use disorder.
There are mainly three levels of use to consider when it comes to substance dependence: 1) recreational use, where the risk is considered acceptable for the individual and society; 2) risky use, which can lead to physical or psychosocial harm in the more or less long term, such as abuse or excess use; 3) addiction, the most extreme level, characterized by the loss of freedom and control over use (Acier, 2016).
In North America, the lifetime prevalence rate for substance-related use disorders (other than alcohol) is 6.1% (Regier, 1990). Canadian national evaluations provide almost the same statistics (Rush el al., 2008). Psychiatric comorbidities (the co-existence of another disorder) are common and higher than in the general population; examples are schizophrenia, mood, anxiety and personality disorders. In addition, patients with substance dependence commonly abuse more than one PAS and poly-substance dependence seems to have become the norm rather than the exception. Substance dependence is a major social problem and a chronic, recurrent psychiatric disorder associated with a number of adverse consequences, be they medical (including physical injuries and psychiatric symptoms), economic or social.
The American Society of Addiction Medicine (ASAM) and the Canadian Society of Addiction Medicine (CSAM) consider addiction or substance dependence to be a primary, chronic and potentially fatal disease involving genetic, psychosocial and environmental factors. This disease affects the brain’s reward, memory and motivation pathways. Clinical manifestations are biological, psychiatric, psychosocial and spiritual.
Substance dependence, like any addictive behaviour, arises from the interaction between risk and vulnerability factors related to the individual, the social-environmental context and the object of addiction. In other words, it is caused by the action of a drug of abuse on a vulnerable brain and usually requires repeated exposure to the substance. This process is greatly influenced by a person’s genetics and the psychological and social context in which the substance use takes place.
Once it becomes dependence, this condition can be chronic and people with it have a very high risk of relapse. This seems to be related to stable, lasting changes in the brain, responsible for long-term behavioural abnormalities (Nestler, 2001). Studies show that 40 to 60% of patients treated for substance use disorders resume active use of substances in the year following discharge from treatment and approximately 40% resume treatment in the first six months (Moore et al., 2014). Relapse rates are even higher for people with substance dependence who use more than one substance, known as multiple substance abusers.
According to Acier (2016), “substance dependence is characterized by the existence of physical dependence related to the adaptation of the central nervous system to a certain threshold of concentration of PAS in the blood and where a reduction of this threshold creates an imbalance in the effects felt (tolerance). This imbalance of the central nervous system is also manifested by a feeling of physical discomfort and psychological angst in situations where the PAS is completely stopped (withdrawal). Psychological dependence refers to the irrepressible need to use the substance to feel the same effects (the individual loses their freedom to refrain from using, which is no longer an option). The absence of the effect of the substances or the fear of their absence creates an unpleasant state (withdrawal) that makes the person start using again. This urgent need to use, despite a decision to stop, can become increasingly strong (craving). The diagnosis of substance dependence encompasses these five dimensions and makes it possible to position the addict on a continuum of severity: loss of freedom, the presence of negative consequences, the existence of tolerance, physical or psychological withdrawal and craving.”