Therapeutic goals and drug properties influence the choice of different routes of drug administration. The inhalation route administers gaseous or volatile drugs or drug droplets to various parts of the respiratory tract. Inhaled drugs are rapidly absorbed into circulation due to the large surface area of the lungs. Inhalation has a localized effect with fewer systemic side effects. Inhaled drug doses, however, are difficult to regulate, and they may stimulate the cough reflex. The intrathecal route injects drugs directly into the cerebrospinal fluid, producing rapid and local effects. If the same drug is given orally, the blood-brain barrier prevents or delays its absorption into the CNS. In topical applications, drugs are applied to mucous membranes of the affected parts for their local effects. Transdermal absorption provides systemic effects, and absorption depends on various factors. This drug delivery route maintains a steady blood concentration and reduces the chances of toxicity. The rectal route is preferred if the patient is unconscious or vomiting. The route can prevent hepatic metabolism and destruction in the stomach.