The 4 methods of drug abuse are ingestion, inhalation, application and:

• A. Injection
• B. Transdermal
• C. Intranasal
• D. Oral

Answer: (A)

Understanding how drugs enter the body is key. The common four routes used to categorize drug abuse are ingestion (swallowing), inhalation (breathing in), topical application (skin or mucous membranes), and injection (directly into the body with a needle). The missing category here is the injectable route, which is distinct from swallowing, breathing in, or applying a substance to the skin. Transdermal is a specific topical method, intranasal is a form of inhalation, and oral is ingestion, so they don’t complete the set. That completes the four main abuse routes, making injection the best choice.