Both exemestane and letrozole may cause drug side effects, but the severity is not comparable and varies from person to person. Both exemestane and letrozole are suitable for the adjuvant treatment of some breast cancer patients, of which both are contraindicated in people who are allergic to the product, premenopausal and pregnant or breastfeeding women, in addition to letrozole is contraindicated in people who are in premenopausal endocrine state, children and adolescents. The most common adverse reactions to exemestane include headache, dizziness, hot flashes (bouts of fever), anorexia, depression, insomnia, abdominal pain, nausea, elevated liver enzymes, increased sweating, pain, and fatigue. The most common adverse reactions to letrozole are arthralgia, hot flashes, nausea, and fatigue. The side effects that may occur after use of the drug are related to the individual’s physical condition, so the specific side effects and the severity of the use of these two drugs are unpredictable, and it is not possible to uniformly compare the severity of the side effects of the two. The specific use of the drug should be under the guidance of a specialist, and should not be used without authorization.