(b) Med.
The act of blowing (a gas, powder, or vapor) into any cavity of the body.
- Webster 1913
There are a variety of reasons why one might want to introduce gases, powders, or vapors into the body's various cavities. For example, during laparoscopic surgery the abdomen is frequently insufflated with carbon dioxide so as to inflate the cavity and give the surgeon more room to work with. Likewise, some radiological procedures employ insufflation to surround the targeted area with inert foreign substances to enhance contrast, or to determine where a blockage has occurred.
In addition to simply enabling other medical procedures, insufflation can be used as a procedure in itself, as a means of administering medicines or other active substances. The skin covering the body is highly effective at keeping the inside in and the outside out. While this is quite convenient for everyday life, it presents problems when you want to introduce something from outside to inside. In contrast, the functions of the interior surfaces of the body often require them to be at least somewhat permeable.
Insufflation can take advantage of this permeability to efficiently deliver active substances to targeted areas. For example, rectal and vaginal insufflation are employed in the context of the "alternative medicine" practice of Ozone Therapy to treat localized discomfort and other problems. Asthma inhalers use insufflation to directly deliver bronchodilators to the bronchi and relieve the symptoms of an asthma attack. The use of cold medications like Dristan which come in the form of spray bottles to be discharged in the nose represent instances of nasal insufflation.
If the substances in question can permeate the mucous membranes lining body cavities and passages, insufflation can also be used to introduce them into the bloodstream. The nose is the most popular site for this use - unlike the rectum or vagina, the nose is conveniently sited for administration, and unlike the lungs, quite some distance from the mouth, an ideal site of absorption relatively close to the nostrils can be found in the nasal mucosa, mucous membranes lining the nasal cavity.
The most iconic example of nasal insufflation for such purposes is the "snorting" of powder, usually recreational drugs like heroin, cocaine, methamphetamine, ketamine, or Ritalin. As the nasal mucosa are highly permeable and link directly to the bloodstream very near the brain, the effects of drugs taken in this manner are felt quickly, often within a minute of insufflation, compared to up to an hour if eaten and absorbed through the digestive tract. This may not always be preferred - for some drugs or situations, the less intense but more prolonged effect caused by delayed, gradual gastrointestinal absorption might be more ideal.
Timing aside, nasal insufflation is simply more efficient, in terms of effect per unit, than ingestion. By avoiding the digestive tract, insufflators eliminate the likelihood that some of their drug will bind to impermeable surfaces or come into contact with digestive acids or enzymes whose purpose, after all, is to break down molecular structures.
The nose does have some of its own defenses, however. The nostrils contain hair for the purpose of trapping foreign substances and preventing them from further entering the body - insufflators may wish to trim their nose hair beforehand, and/or immediately after insufflation rub their finger around in the nostrils to dislodge powder and then snort it further up to the mucosa. Snorting a few drops of water can also be effective for this purpose.
Additionally, snorted powders will irritate the nasal mucosa and other nasal surfaces. For one thing, this will hurt, although many drugs taken in this way have an anaesthetic effect that will lessen the pain. Even if pain is not felt, however, insufflators should keep in mind that this irritation can damage the nose, leading to bleeding, a weakened sense of smell, and erosion of the septum, especially with frequent administration.
Even those users focused on experiencing the drug's effects to the exclusion of all health concerns should take note: irritation will cause the nose to secrete mucus which will attempt to perform its proper function of binding to the foreign substance and carrying it away, preventing it from entering the bloodstream. This is the cause of the unpleasant runny nose and post-nasal drip experienced after insufflating powders. To minimize this effect, users might want to make sure their drugs are as finely powdered as possible, so as to reduce the irritating effect. Those who can overcome an aversion to "eating boogers" may be able to salvage some of the bound substance by rubbing the secreted mucus into the absorptive membrane of the gums.
As a route of administration, though insufflation may be more effective than ingestion, it may be surpassed in efficiency by injection (intravenous, intramuscular or subcutaneous), inhalation (smoking), or rectal absorption by suppository. Of course, some inefficiency might not be a bad thing. On the one hand, the same mechanisms that filter out the substance you want does the same to the impurities you don't. On the other, if the substance is more pure or potent than expected, lower efficiency also means an decreased risk of overdose, and the mechanism of insufflation makes it easier to administer the drug in smaller doses, giving time to evaluate the effects and decide whether to continue further.
Also, compared to injection or combustion and inhalation, insufflation generally requires less preparation, is more difficult to do improperly, and is generally less dangerous as an activity in and of itself. Besides, not many people want to put drugs in their ass. In general, insufflation tends to be a reasonable "middle ground" method of administration.
All that said, let me note that there's no fundamental linkage between illegal drugs as chemical substances and nasal insufflation as a method of administration. Rather, it is the high price and volatility of supply characteristic of black markets which spurs the users of illegal drugs to attempt to extract maximum effect from minimum intake. Were prohibitions on the manufacture, trade, and use of such substances lifted, it is likely that many users would prefer oral administration. In the 1800s and early 1900s, when cocaine and opiates, heroin included, were legally available as medicine, they were usually marketed in tablet or liquid forms.
Inversely, there is nothing beyond distaste preventing individuals from insufflating legal substances. I once ground up and snorted Excedrin to make a headache go away right now. Insufflating powdered caffeine or other stimulants like ADD medications is relatively common among college students, and Viagra is snorted by those whose need for a stiffer erection can't wait another 30 minutes. Snuff, a powdered form of tobacco prepared for nasal insufflation, has been used for several centuries, though it is relatively uncommon today.
Having said all that, now for some lighter business. Here's a mnemonic tune I thought up a few years back to help my friends remember the mechanism of nasal insufflation.
Insufflation
(to the tune of Frere Jacques)
Insufflation
Insufflation
Up the nose!
Up the nose!
Through the mucous membrane
Through the mucous membrane
There it goes.
There it goes.