Answer:
In sublingual administration, the drugs are placed under the tongue where it gets dissolved and absorbed. After gets dissolved the drug diffuses through the mucous membrane and gets absorbed quickly by the tiny blood capillaries present beneath the tongue.
This mode of drug administration have some advantages like small doses are required as no metabolism takes place because it does not get into the digestive system. This method is quick because it is directly absorbed in blood so it is helpful in case of emergency.