Weight gain is a common side effect of Premarin use. Significant change in body weight often occurs early on in the course of Premarin usage, according to Drugs.com.
Premarin is commonly used to treat symptoms of menopause that are associated with a drop in estrogen levels, according to RX List. These symptoms may include hot flashes, vaginal discomfort and possible osteoporosis. Beginning use of Premarin as an estrogen replacement is often accompanied by symptoms similar to menstruation or the addition of birth control, such as bloating, weight gain, appetite change and mild nausea. More serious side effects are rare but may include symptoms such as migraines, jaundice and chest pain.