fasenra is not a rescue medication or for other eosinophilic conditions. fasenra may cause allergic reactions. get help right away if you have swelling of your face, mouth, and tongue, or trouble breathing. don't stop your asthma treatments unless your doctor tells you to. tell your doctor if you have a parasitic infection or your asthma worsens. headache and sore throat may occur. this is the sound of fasenra. ask your doctor about fasenra. if you can't afford your medication, astrazeneca may be able to help.