Which form of medication consists of solid or semisolid adhesive masses that prolong contact at the application site?

The correct answer is that plasters consist of solid or semisolid adhesive masses designed to prolong contact at the application site. Plasters are typically made of a medicated material that adheres to the skin, allowing for the slow release of the active ingredients over a longer period. This property makes them particularly useful for delivering medication locally to an affected area, ensuring consistent therapeutic effects without frequent reapplication.

In contrast, patches also serve a similar purpose by delivering medication transdermally but are typically more flexible and designed for systemic absorption. Liniments are liquids or gels used for rubbing on the skin for relief of pain and stiffness, not designed to provide a prolonged contact as they generally evaporate quickly. Gels are often semi-solid formulations used for various purposes, including topical delivery, but they do not have the same adhesive properties that plasters possess. Therefore, plasters are distinct in their formulation and application, making them the correct choice for this question.