Autonomously administering a pharmaceutical agent to an animal. A tag assembly is affixed to an animal. The tag assembly may be an ear tag, although other configurations can be used. The tag assembly has a reservoir that houses a pharmaceutical agent. An actuator and an application mechanism are provided. A control signal is generated responsive to an input, which may be from a sensor associated with the tag assembly or may be from an external circuit located apart from the tag assembly. Receipt of the control signal causes the actuator to apply a force to the reservoir, which in turn induces a flow of the pharmaceutical agent, via the application mechanism, to a body of the animal. The pharmaceutical agent may be topically or intravenously applied. The pharmaceutical may be an insecticide or some other agent. Multiple reservoirs can be provided to dispense the same or different pharmaceutical agents.