Generally speaking, all drugs are alien to the body and create the same physiological effects as taking a poison. Since they are not a food source, the body reacts to drugs by attacking the substances and doing all it can to remove it from the blood stream.
If the ingestion of drugs continues and the blood levels of the drugs continues to increase, the body will then slow down all of its functions in an attempt to keep these poisons from reaching the brain.
At this time, the cleansing organs are still working on getting the drugs our to the body and, since this process isn’t as effective as needed, the body pushes these substances into dormant fat tissue.