Final answer:
Sublingual medication is absorbed directly into the bloodstream via blood vessels beneath the tongue, providing a fast and efficient method of drug delivery that bypasses the gastrointestinal tract.
Step-by-step explanation:
Sublingual medicine enters circulation by being absorbed directly into the blood vessels that are located beneath the tongue. When a drug is administered sublingually, it diffuses through the mucous membranes that line the mouth. Sublingual glands, which lie below the tongue, are part of the oral mucosa and can quickly absorb substances into the extensive network of capillaries located here. This allows the medicine to move through the bloodstream without first entering the digestive tract and being metabolized by the liver, which preserves its potency and enables a rapid onset of effect.
Drugs administered intravenously reach plasma levels substantially higher than those achieved by oral or intramuscular administration, but sublingual administration is still a preferred method for certain medications due to its convenience and efficiency. This method bypasses issues of GI tract absorption, which is critical for patients who cannot take medicine orally due to vomiting or an inability to swallow safely. Hence, sublingual administration is not only convenient but also effective in delivering drugs directly into systemic circulation.