Some relationships between addiction and drug delivery to the brain.

Hemodynamic radioisotope studies of brain blood flow in humans have been correlated with the delivery of some common addictive drugs. Both lipophilic and hydrophilic tracers were used in the hemodynamic studies. Iodoantipyrine is lipophilic and is completely cleared by brain during a single brain circulatory passage, as are cocaine and nicotine. Iodohippurate is hydrophilic, so its brain clearance after IV injection resembles that of morphine. The earlier studies performed in humans have been related here with recent studies of blood brain penetration of drugs of abuse. As presented, these separate studies are consistent with the proposed hypothesis that the interval between drug intake and perceived effect is a significant consideration when explaining severity of addiction. The shorter the time interval between drug intake and its perceived effect, the more severe the addiction appears to be. This relationship may explain differences in severity of addiction to the same drug taken by various routes of administration.