P O is by mouth
I V is intravenous
I M is intramuscular by needle
SubQ is just under the skin by needle
topical is absorbed through skin (by cream/ointment/patches)
some meds can also be inhaled
and yes, meds can even be administered through the rectum
also eyes
Medicine are administered depending on their mode of action. Some ways are orally through pills, topically through ointments or sprays or by injection into veins, muscles or fat.
Medications can be administered by many routes such as orally, topically, intravenously, sublingual, anal, inhalation, vaginal, IV and ocular (for example, eyedrops).
It all depends on what type of medication you are taking or need to administer. Many medications are in pill form and could take it by mouth, as well as liquid forms of medication. Some medication requires administration via needle or in some cases, there are medications that are administered in the anus (although these are rare).
Diiferent ways to adminster medication are through injection with a needle and syringe, orally in the form of a liquid or pill, anally in the form of a suppository.