> Surely the percentage varies significantly depending on the drug.
It actually doesn't, which is one of the key findings of addiction research. The reason is that people don't abuse drugs because of the physical discomfort of withdrawal, but rather because they have a psychological dependence on drug use. And that psychological dependence is caused by things like previous life trauma; any given drug is just an interchangeable object that's being fit into a slot.
The one drug-related variable that is important though is route of administration. Because addiction involves linking an action with a reward, the faster a drug takes effect the more likely a user will form a problem with that substance. So basically in terms of addictiveness:
By this reasoning smoked marijuana is equally as addictive as nicotine and more addictive than snorted cocaine or orally ingested opiates (i.e. prescription painkillers). That seems pretty suspect to me.
That rule applies JUST within the same substance. And only generally, some exceptions exist for poor bioavailability due to absorption differences and particular metabolic pathways.
The idea is that the shorter it takes to get into the bloodstream/brain, the peak effects are stronger, and the downregulation of neuron receptors is more acute and lasts longer (therefore requiring redoses to activate them).
Any links to such research? It's hardly presented in a scientifically rigorous way, but take this for example: http://bakadesuyo.com/2012/08/whats-the-most-addictive-drug/. It supports the notion the delivery significantly impacts behaviour, but it also cites highly variable addiction rates - not a consistent 90%. Still Googling for better research, but suffice it to say I'm a bit skeptical of the claims...
Not sure about primary sources, but the professor talks about the routes of administration in the Drugs and Behavior class that's available on iTunes. In terms of addiction rates, this is something that Carl Hart researches and has been talking a lot about recently. He has written a bunch of articles and given some TED talks on the topic.
In terms of quoted figures for the addictiveness of various substances, you need to look at whether the studies you're looking at correct for the characteristics of the users. E.g. people who use heroin are much more likely to become addicted to drugs, which makes heroin look more addictive than it actually is. There certainly is some variance between drugs, but it's relatively small... like 9% vs 13%, but not like 2% vs 90%.
It actually doesn't, which is one of the key findings of addiction research. The reason is that people don't abuse drugs because of the physical discomfort of withdrawal, but rather because they have a psychological dependence on drug use. And that psychological dependence is caused by things like previous life trauma; any given drug is just an interchangeable object that's being fit into a slot.
The one drug-related variable that is important though is route of administration. Because addiction involves linking an action with a reward, the faster a drug takes effect the more likely a user will form a problem with that substance. So basically in terms of addictiveness:
smoking > mainlining > snorting > eating > topical
This is why different drugs seem like they have different addictiveness potentials.