By the end of postgraduate training, using a patient-centred approach and appropriate selectivity, a resident, considering the patient’s cultural and gender contexts, will be able to...
Intoxication is that acute phenomenon whereby one is "under the influence" of a toxic substance, the short term experience of a substance acting on the mind and body.
Drug abuse, on the other hand, is the phenomenon whereby the use of a substance creates ongoing problems in a person's life. From a hero of a doctor who is a legend in Vancouver, Canada, and the world.
Dependence is the physiological dependence a person can have on a substance, whereby they would experience symptoms of withdrawal without it.
Putting all of the concepts together with an example: I drink a lot of coffee. I drink it to the point that I have an increased ability to concentrate and a decreased need for sleep. It is, one could say, very mildly intoxicating. I consistently consume it so much that I have now become dependent on it, as evidenced by the fact that I have developed tolerance to it (it takes me two cups to get the same effect that one cup used to have), and when I don't have it at all, I get a withdrawal headache and am objectively irritable. Although you may think I'm in denial, I would argue that I do not have an addiction to coffee, or in other words, I don't feel it's a substance that I abuse, because it is not wreaking havoc on my health, social relationships, or aspirations in life (arguably because I don't have to go through the withdrawals from it, with at least one Starbucks on every Vancouver street corner). If, on the other hand, society considered it a harmful substance, and I could no longer easily consume it, I could very well be someone considered to have a drug addiction (because I can't imagine not going out of my way to ingest it, certainly losing a relationship or two over it if they tried to make me choose!). The concepts of drug abuse and other notions of addictions (such as gambling or disordered eating) are not insignificantly laden by the values of society.
In any case, one could categorize coffee as a stimulant. Stimulants in general lead to hyperarousal, manifested by increased mental alertness, pupillary dilation, and other physiological fight-or-flight responses. It gets the body more prepared for action! Examples of common stimulant drugs of abuse include cocaine and methamphetamine, both of which exert their addictive properties largely by increasing the amount of dopamine floating in the brain, which is a neurotransmitter that signals reward. Good job, you just smoked crystal meth!
Depressants, on the other hand, are the downers to the uppers, literally being referred to as "down" by patients I see from the Vancouver Downtown East Side. (Sadly, they just call it down not as an easy-to-say shorthand, but rather because of all the fentanyl contamination, no one quite knows just what kind of opioid they're ingesting/smoking/shooting/etc.) Depressants, such as benzodiazepines and alcohol, exert their effect by increasing inhibitory neurotransmission in the brain, slowing the body down so much it may even stop breathing (as can happen in a depressant drug overdose). Opioids are a powerful class of substances with depressant types of effects that act directly on receptors on the brain that give a sensation of euphoria, mimicking the natural endorphins our bodies may release when we have a physiological reason to experience a natural high.
And then there are the hallucinogens, the catch-all other category that cause psychedelic reactions and that can literally fry your brain. Acid and LSD are not your friends, although MDMA may make you think you have more friends. The only common linkage in this category of substances really is that most have a common action on at a type of serotonin receptor.
I once heard someone explain to me that people tend to repeatedly go for the drugs that they benefit from, that satisfy a need in their life. Like for me, caffeine for my desire for less sleep. It is important to never presume someone does or doesn't use substances regularly or occasionally, as this also means you are making a preliminary judgment about what they need or desire in their life. And to miss out on this critical piece of historical information can have consequential repercussions on your ability as their physician to provide patient-centered care. After gathering the history of the presenting illness and a review of systems as indicated, I gather a patient's past medical and surgical history, ask about allergies, ascertain a medication history, and then gather a family history and social history, the latter of which includes an inquiry into substance use (much like the HEADSSS social history for adolescents), which is pretty well the standard historical template in medicine, give or take. By asking about substance use, in a thoughtful way, you also set the understanding that you are aware that substance use is a common and important enough thing to discuss.