common side effects include thrush, headache, and cough. serious side effects may include worsening asthma, anaphylaxis, seizures, and heart problems. safety in pregnancy and breastfeeding is unclear. fluticasone, a corticosteroid, works by decreasing inflammation while salmeterol, a long-acting beta-adrenoceptor agonist (laba), works by activating beta-2 adrenergic receptors.