Common Side Effects

• According to the Mayo Clinic, side effects of Premarin 0.3 mg that are considered common but not serious include pain in the abdomen or back, acne, clear vaginal discharge and minor swelling or soreness of the breasts.
  
  

Serious Side Effects

• Serious side effects of the 0.3-mg dosage, as cited by PDRHealth, include vomiting, hypertension, high blood sugar, fluid retention and vaginitis . A patient experiencing these symptoms should consult with a physician before continuing Premarin doses.
  
  

Severe Side Effects

• The Mayo Clinic cites severe side effects associated with Premarin 0.3. mg as confusion, fainting, pain in or behind the eyes, difficulty breathing, chest pain and unusual vaginal bleeding. These side effects require emergency medical attention.
  
  

Existing Medical Conditions

• Before using Premarin 0.3 mg, a patient should advise her physician of existing medical conditions such as kidney, gallbladder or liver disease, epilepsy, asthma, migraines, lupus or high calcium levels in the blood.
  
  

Drug Interactions

• Premarin 0.3 mg has the potential to adversely interact with blood thinners, steroid medications, tricyclic antidepressants and St. John's wort, as well as with medications used to treat epilepsy and diabetes.