Why Users Inject Heroin
Is It Greed, Gluttony, or What?
Only recently, with the high purity levels of street heroin, has it become well reported that heroin may be ingested in a manner other than injection. This has, in fact, caused those leading the Drug War no end of consternation. First, their vicious war seems to have made matters worse (from their perspective): heroin is cheaper and more available than when they started. Second, they have to fight the propaganda portion of their war on a whole new level. This brings us the current wave of Partnership for a Drug Free America anti-snorting heroin ads: "This is your brain. This is what happens to your brain when you snort heroin." (Check out "Why Purity Has Increased" for a history lesson on the unexpected results of the Drug War.)
It is true that one reason that heroin has traditionally been injected is that the street heroin purity levels have been so low. It reached its nadir in 1970 at about 3%. But even at this low level of purity, a novice could certainly have gotten high smoking without mortgaging the house. This is not to say that price and quality do not have an effect on the administration route; they do; but they are not the only factors.
As an example, let's look at the situation during the first few years of this century, when heroin could be bought over the counter--just like aspirin. At that time, it was mostly administered orally. This usually took the form of heroin cough drops. (Imagine that: cough drops that actually work!) The point is that people weren't dissolving these things and injecting them--just like people don't inject alcohol or nicotine today.
But there is a reason that heroin is naturally associated with intravenous injection. Heroin is the least stable of all the opioids. Whereas morphine and codeine have half-lifes in the human body of about three hours (and the synthetic opioids can have half-lifes measured in days), the half-life of heroin is about two minutes. When heroin breaks down, it becomes morphine, primarily.
Heroin is usually reported as being two to three times as potent as morphine (check out "Two to Three" for a discussion of what this really means). But this gives the wrong idea about heroin because it does not actually get the user high. Heroin acts as a transport chemical, delivering more morphine to the brain because it crosses the blood-brain barrier more quickly than morphine. Once in the brain, it is morphine that heroin breaks down into that gets the user high.
So if heroin breaks down into morphine before crossing the blood-brain barrier, it is much less efficient: about 1/3 as efficient. With a half-life of two minutes, most of the heroin ingested orally breaks down into morphine. More or less the same thing happens when inhaling. Inhalation is a very efficient means of ingesting drugs--there is very little drug loss. But it is slow and as a result, most of the heroin inhaled is converted to morphine before it reaches the blood-brain barrier.
Heroin is most effective when administered in a way that delivers it to the blood stream quickly: intravenous injection, subcutaneous injection, and smoking. This is why it does make more sense to inject heroin than other drugs--morphine, for example.