dcoes it go through the lungs or just leak down the throat mostly? how does it get to the brain so fast?
Directly into the bloodstream through the mucous membranes in your sinuses.
The drug is absorbed through the mucous membranes that line the nasal passages. From there it passes directly into the bloodstream.
Heh, you probably would have beaten me, Q.E.D., had I bothered to type a complete sentence. 
so how concentrated is the drug snorted as compared to shot?
It’s less a matter of concentration, and more one of time. IV drug use delivers the dosage into the bloodstream almost immediately, whereas a snorted dosage takes time to diffuse across the mucous membranes. The reason many hereoin addicts inject their fix IV is because the effect is faster and more powerful.
From this website:
http://www.druglibrary.org/schaffer/dea/pubs/abuse/chap4/stimula/cocaine.htm
“The intensity of the psychological effects of cocaine, as with most psychoactive drugs, depends on the dose and rate of entry to the brain. Cocaine reaches the brain through the snorting method in three to five minutes. Intravenous injection of cocaine produces a rush in 15 to 30 seconds, and smoking produces an almost immediate intense experience.”
Hence the popularity of smoking and needles, and the ultimate demise, before their time, of those who take a ride on that train.
Yes, the difference between intranasal and intravenous administration of drugs is basically a matter of time. Intravenous injection allows drugs to reach the brain very quickly – in the time it takes for it to circulate through the veins to the heart and then to the brain. (Intraarterial injection would be faster, but it is extremely dangerous and probably not often tried since 15 to 30 seconds is probably fast enough.)
Intranasal administration would be limited by the time taken for the drug to diffuse through the nasal membrane into the nearby capillaries, then from the site through the venous system, heart, and arteries until it reaches the brain. (Of course, the drug diffuses within the blood vessels as well, and throughout the body afterwards; it’s not travelling to the brain in a neat little bundle, though once it starts binding to receptors it probably has higher concentrations in the brain than anywhere else.)
Incidentally, applying a drug to any mucous membrane would have the same effect. (Taking inventory of such membranes will be left as an exercise to the reader.) The method is slower than injecting, and slower than smoking, but faster than the oral route. Few medical drugs are used intranasally, and those that are are sprays, not powders. What many people probably don’t understand is that drugs such as xylometazoline (Otrivin) or phenylephrine (Dristan) are systemic drugs being delivered intranasally. They’re nasal mists because that allows them to be absorbed rapidly, not because they ‘work right at the site’.
The OP doesn’t mention it, but it’s been mentioned – smoking a drug is even faster than IV injection. I guess this is mostly because blood travels relatively slowly in veins compared to arteries. Once the drug diffuses through the alveolar membrane, it should be able to reach the brain quite quickly, without having to make the slow trip through the user’s arm in order to get there. Intrapulmonary (?) administration of drugs does occur in medicine – asthma inhalers are a good example – but the drugs are formulated as mists rather than smoked.
Many drugs which are not very effective when taken orally (this is the notion of ‘bioavailability’, the fraction of drug absorbed via the oral route). When drugs are taken orally, you have all kinds of things to contend with – the low pH of the stomach, digestive enzymes, and so on. Another factor to consider is ‘first-pass metabolism’. When drugs are taken orally, they will pass through the liver before they reach the brain. They will be subjected to a host of detoxifying enzymes, and many drugs can’t tolerate this. (Other drugs depend on the liver to change an inert substance into an ‘active metabolite’ – codeine is a notable example, along with some antihistamines.) Heroin happens to be one of the drugs that does not stand up well to first-pass metabolism. This, rather than the intensity of the high, is the real reason why heroin is snorted or injected.
One last thing. Yes, cocaine and heroin users do die before their time. I recall reading that it was about 5 years for heroin; cocaine might reduce life expectancy by more than that, because it’s toxic to heart muscle, among other things. Likewise methamphetamine. But (this won’t come as a shock) the drug that reduces life expectancy the most, by far, isn’t a ‘hard’ drug, or even illegal – it’s tobacco.
Yes, but since it’s legal, it’s God’s very own sacrament. [/sarcasm]
It’s not just the mucus membrane from the nose and sinuses that absorb the drug, but the mucus membranes in the mouth and further down, hence, the nose and mouth get numb. I remember “back in the day” that the fine grains snorted would make its way down to the mouth in a thick ball of snot, numbing the tongue and the walls of the mouth like a euphoric local anesthetic.
I never smoked or injected. Hearing the horror stories, plus seeing some people get addicted by just snorting, I feel this was a good thing.
Well, if you’re crushing pills and snorting them, you might also be introducing foreign, nonabsorbable substances to the nasal passages. Dr.J once treated a woman for horrible sinus problems that turned out to be apergillus growing in her sinuses. She’d been snorting Lortab, and the pills had been contaminated with spores. She snorted the spores with the drug, and they lodged in her sinuses, sprouted, and grew quite nicely.
Apparently, growing fungus in your sinuses turns your snot nearly black. I heartily DON’T reccommend it.
When I mention this, I often get asked why anybody would inject drugs at all, ever, since smoking gets it to the brain faster.
Of course, there is the consideration that smoking some drugs is difficult, like heroin where you have to perform a tricky ritual called “chasing the dragon,” allowing the drug material to vaporize on top of a heat source and inhaling the fumes rather than just lighting up a heroin cigarette.
But come on, surely the hassle of smoking, even when it is difficult like that, is nothing compared to the hassle (for all but the most dedicated users) of actually finding a hypodermic syringe, getting the drug into some kind of solution, filling the syringe with the drug solution, and finally actually sticking a sharp metal object into your skin and digging around until you find a vein (and as you said, Roches, it must be a vein and definitely not an artery[sup]1[/sup], so you have to make sure the blood flash that appears in the syringe is not bright red) and squirting a bunch of foreign material directly into said vein.
So why would anybody go through all that trouble instead of smoking it, when smoking gets your brain dosed up earlier? Because, alas, many drug users don’t care so much about having the effects start kicking in a few seconds earlier – even though shooting up takes a little longer to kick in compared to smoking, it allows the user to hit the brain with an extremely high dose of heroin (or whatever) all at once, much higher than could possibly enter the bloodstream through alveolar diffusion in a comparable period of time. Thus, the user has the drug’s effects kick in a few seconds later, but they kick in all at once, in an amazingly intense tsunami of euphoria, the famous “rush” that many drug users seek, which I have usually heard described as a whole-body orgasm[sup]2[/sup].
I would not be at all surprised if cocaine and heroin users, on average, die early; in fact, it would greatly surprise me if most of the people I’ve talked to weren’t dead a lot sooner than five years before their time.
(My interviewees are almost all heroin users, generally not regular users of cocaine, though of course many if not most had tried it.)
And I would not be surprised if cocaine and other stimulants, being cardiotoxic and all, reduce life expectancy too.
But I am skeptical that opioids in general reduce life expectancy. I mean, some opioids clearly have dangerous effects, like the apparent link between hydrocodone and hearing damange. But I’m not aware of any life-shortening effects that are opioid-universal. For instance, I wonder if otherwise healthy patients on long-term methadone maintenance suffer from a decrease in life expectancy. I haven’t seen any studies indicating that they do … but given the possible past health abuses of a lot of methadone patients, they may have already done life-shortening damage, which would complicate studies. I guess one would need to find people who hadn’t done that kind of serious damage in the past, and see how long they live. That would take a long time, though. Hmmm.
[sup]1[/sup]I suppose you could inject into an artery, if you want the tiny insoluble particulate matter in the injected liquid to clog up capillaries and cause massive pain and tissue death, possibly resulting in digit and/or limb loss … hey, nobody said being an injecting drug user would be a walk in the park!
[sup]2[/sup]Of course, not all drug users are after this kind of super-intense rush, and those that aren’t usually stick with smoking, snorting, or swallowing. Interestingly, the people I’ve talked to who were primarily interested in a pleasurable rush usually didn’t seem to care which type of drug they took to get it. Even if they usually used, say, heroin, they often said that they had no problem injecting cocaine or amphetamines if they couldn’t get heroin – even though heroin and cocaine / amphetamines are completely different drugs with opposite effects. One of the subjects I interviewed was currently abusing levodopa, prescribed to him for a Parkinson’s-like condition, the same way he had abused heroin and cocaine in times past – looking for a rush.