NK1 receptor antagonists are used to treat nausea and vomiting caused by chemotherapy. These medications work by blocking the neurokinin-1 (NK1) receptors in your brain, which helps prevent the feeling of nausea. NK1 receptor antagonists come in different forms, including oral pills and injectable solutions. Examples include aprepitant (Emend), fosaprepitant (Emend for injection), and rolapitant (Varubi).