Drugs that interact with receptors so as to block the action of agonists or the naturally occurring chemical messenger are called antagonists. For example, atenolol is a ß1 antagonist. Can you think what it might be used for?
Remember that activation of ß1 receptors raises the heart rate and a ß1 antagonist will therefore prevent this action. Consequently atenolol is used to slow the pulse and control high blood pressure. Because of its mode of action atenolol is often referred to as a beta blocker.