It is important to know who should not take this drug before taking it. People who are allergic to the active ingredient in Synjardy or finasteride may experience mild side effects when they use it. People who have had a history of certain medical conditions should consult their doctor prior to taking the drug. In addition, women cannot take finasteride because they risk developing breast cancer due to the similarity of this compound with steroid hormones in female body that might cause these abnormal cells, and thus lead to breast cancer if menopause occurs earlier than usual as a side effect of Synjardy.