When drug molecules are bound to plasma or tissue proteins, they are typically considered:

When drug molecules are bound to plasma or tissue proteins, they are generally considered inactive because their binding to these proteins decreases their free concentration in the bloodstream. This means that a smaller fraction of the drug is available to exert its therapeutic effect.

Drugs must be in an unbound form to freely circulate and interact with their target receptors or tissues to produce a pharmacological effect. When a drug is bound to proteins, it is often rendered inactive until it is released from the binding sites. This concept is crucial in pharmacology, as it helps explain the dynamic balance between the active (free) and inactive (bound) forms of a drug in the body, which ultimately influences drug efficacy and dosing.

In contrast to this, options related to metabolism, excretion, or potency do not directly pertain to the state of drug molecules bound to proteins. Metabolized suggests chemical alteration of the drug, excretion refers to the elimination process from the body, and being more potent implies a stronger effect of the drug when active, which is not applicable when the drug is in a bound state.