It`s not best method to take undiluted to mouth, it is too strong if it is strong undiluted IMO, and you gain more benefit from oil of oregano if you mix it real good with other oil, i use olive,hemp seed oil, coconut oil is also good as it is also anti-fungal.
By mixing it to other oil you can up the dosage and the oregano oil will also spread better in to the intestinas, i mean the mixture will go longer in tube .
Oil of oregano is those strong ones, it can also kill good flora so take good probiotics also.