You can use oil of oregano to treat sinus problems, according to both Earth Clinic and Natural Society. WebMD concurs that oil of oregano is used to treat respiratory tract disorders but warns that insufficient evidence exists as to its efficacy.
Earth Clinic recommends taking oil of oregano orally by placing a drop or two of oregano oil beneath the tongue. Alternatively, adding several drops of the oil to a steaming pan of water and inhaling the vapors is effective, too.
According to WebMD, possible side effects of oil of oregano include allergic reaction and mild stomach upset. Oil of oregano can also affect the way in which the body excretes lithium, so a change in dosage might be necessary for those who use lithium with oil of oregano.