What term refers to a drug or chemical that inhibits or blocks the action of neurotransmitters?

The term that describes a drug or chemical that inhibits or blocks the action of neurotransmitters is "antagonist." An antagonist functions by binding to neurotransmitter receptors and preventing the natural neurotransmitter from having its usual effect. This can lead to a decrease in signaling activity within the neural pathway, resulting in reduced physiological responses that would normally be activated by the neurotransmitter.

For instance, in the context of pain relief, certain drugs act as antagonists by blocking pain-related neurotransmitters from binding to their receptors, thereby reducing the sensation of pain. This mechanism is crucial in various medical treatments where controlling or dampening neuronal communication is necessary for therapeutic outcomes.