From Coca Ricky:
The golden rule: Only fools snort powders.
Never, ever, snort a powder. Heres why;
1) Powders destroy the mucousal membranes of the nose.
2) Only a portion of the cocaine powder will enter the bloodstream rapidly enough to create a psychotropic effect, the rest is wasted.
3) Powder has a much slower onset of effect, this means a less intense high.
This is why these facts are true;
1) The physical trauma of the micro-granules of a powder shooting through the nasal cavity at a high velocity causes micro-cuts on the nasal membranes. Not only does this just damage the mucousal membranes and thus damage the nose, but this damage to the mucousal membranes also, overtime and repeated exposure, reduces the ability of the nasal mucousal membranes to absorb as much cocaine. This progressively less and less cocaine is able to be utilized by the nose. Secondly, the powder also dries out the nasal mucus and can cause damage to the nasal mucus glands and result in less mucus production for weeks/months after a moderate cocaine binge. Again, impeding on the effectiveness of repeated use.
2) When you snort a powder, any powder, including cocaine, before it can enter the bloodstream through the mucousal membranes it must first dissolve into a solution. Your nasal cavities mucus dissolves the powder into a solution, and that solution then absorbs through the mucousal membranes in a aqueous-mucousal-solution. Unfortunately your nasal cavity only has so much mucus inside it at one time. Thus what happens is only a portion of the powder you snort, is dissolved into a solution and thus able to enter the bloodstream, shortly after insufflating the cocaine powder. The remaining cocaine powder, which can be a significant amount, especially after repeated use, sits in the nose as a powder unable to dissolve due to the available mucus being used up. Thus, this remaining cocaine powder can sit there sometimes for hours after snorting, and slowly dissolves and enters the bloodstream as more mucus is produced. This happens over hours, and thus you get a very small amount constantly entering the bloodstream, never a large enough amount to accumulate to a pyschotropic effect. Therefore, only the first amount snorted, when the largest amount of mucus is available, will give a psychotropic effect. The remainder that seeps in over hours, wont give any effect, yet can be a large amount of the cocaine you snorted. For example if you snorted 100mg of cocaine, and 50% dissolved with the available mucus within 15 minutes, the remaining 50% would dissolve slowly at just a few % an hour, for the next several hours, thus your wasting that remaining 50%.
3) When you snort the cocaine powder, or any powdered drug, before it can enter the bloodstream it needs to be dissolved into a aqueous-mucousal-solution via the nasal cavities mucus. This process can takes at least 5 minutes to dissolve a sufficient enough amount to begin creating a psychotropic effect, and will continue to buildup that effect slowly over 15-30 minutes.
He's talking about cocaine, but it's all obviously applicable to any powdered substance.