Oral mucosal drug delivery is an alternative method of systemic delivery with several advantages over both injectable and enteral methods. Drugs that are absorbed through the oral mucosa directly enter the systemic circulation, passing through the gastrointestinal tract and first-pass metabolism in the liver due to oral mucosa being highly vascularised. This results in rapid onset of action for some drugs because of a more comfortable and convenient way of delivery than the intravenous one. But not all drugs can be administered through the oral mucosa due to characteristics of the oral mucosa and physical and chemical properties of the drug.