If you've never heard of sublingual administration of medication, then the HCG diet under tongue might be something new to you. The surface underneath the tongue has many blood vessels and mucosa. If you swallow medication, it goes through the digestive process and in many cases, disintegrates to useless chemicals in the body. When placed under the tongue, medication goes directly into the blood stream due to the many vessels and mucosa in the region. That's one reason the diet drops under tongue work.