What method involves inhaling substances into the lungs through smoking or huffing?

The method that involves inhaling substances into the lungs through smoking or huffing is known as inhalation. This route of administration allows substances to enter the bloodstream quickly through the alveoli in the lungs, providing rapid onset of effects. Inhalation is commonly used for various substances, including tobacco, marijuana, and certain volatile chemicals, due to its efficiency in delivering drugs directly into the systemic circulation.

Other methods listed, such as oral administration, transdermal, and rectal administration, involve different pathways and physiological processes that do not include inhaling substances into the lungs. Oral administration requires substances to be absorbed through the digestive system, transdermal involves absorption through the skin, and rectal administration involves absorption through the rectal mucosa. Each of these methods has its own specific characteristics but does not encompass the act of inhaling substances as inhalation does.