Some medicines can be given sublingual, which means "under the tongue". The reason for this method of administration is that some medications can enter the bloodstream better or faster this way.
For example, B12 is a vitamin that for decades was given as an injection because when someone has Pernicious Anemia they cannot absorb it from the intestines due to a lack of a chemical called intrinsic factor that "grabs" it and pulls it into the bloodstream. A few years ago it was noted that if given sublingual, it would be adequately absorbed, eliminating the need for an injection.
Another example is when a patient in Hospice care is near death, unable to swallow but having pain, the pain medication can be given as a liquid under the tongue, where it is absorbed quickly and gives rapid pain relief.
A pill designed to be given orally will rarely be able to be administered sublingually. A pharmacist can tell you if a certain medication has a coating and absorption profile that will allow this form of administration.
An example of a pain medication intended to be taken orally that can be taken sublingually, if you don't mind a slight bitter taste, is hydrocodone. Approximately 1/3 of an oral dose has the same effects when taken sublingually. This method of sublingual dosing has been tried when a patient's Dr. does not prescribe enough of the medication in quantity to be taken orally to subdue the patient's severe pain.