Which method of taking a drug will cause it to reach the brain most quickly? taken by mouth injected directly into the bloodstream inhaled through the nose absorbed through the skin?

The fastest way of getting drugs into the brain quickly is by smoking it. The second is by injecting it into the bloodstream and, in the third place is considered to be inhalation of the drug or also known as snorting. The reason why smoking a drug is considered to be the fastest way to get a drug towards the brain, it is because the smoke that came from the drug, gets into the lung blood which travels towards the brain, which is why cigarettes are considered to be addicting.

Gay-lussac's law i think.