In the treatment of tamoxifen, the most frequent adverse reactions associated with its anti-estrogenic effect, manifested in the form of paroxysmal sensations of heat ("hot flashes"), vaginal bleeding or discharge, itching in the genital area, alopecia, pain in the area of the lesion, ossalgia, weight gain .
Less frequently or rarely, the following adverse reactions were observed: fluid retention, anorexia, nausea, vomiting, constipation, fatigue, depression, confusion, headache, dizziness, drowsiness, fever, skin rash (including occasional reports of multiform erythema,Stevens-Johnson syndrome and bullous pemphigoid), visual impairment, including corneal changes, cataract and retinopathy, retrobulbar neuritis, allergic reactions, including angioedema; decreased libido in men, impotence. Interstitial pneumonitis was rarely observed. At the beginning of treatment, local exacerbation of the disease is possible - an increase in the size of soft tissue formations, sometimes accompanied by a pronounced erythema of the affected areas and adjacent areas, which usually occurs within 2 weeks.
The likelihood of thrombophlebitis and thromboembolism may increase.
Often leg cramps are noted.
Transient leukopenia and thrombocytopenia, as well as an increase in the activity of "liver" enzymes, very rarely accompanied by more severe impairments of liver function, such as fatty liver infiltration, cholestasis and hepatitis, can rarely occur.
An increase in serum triglyceride concentrations in some cases combined with pancreatitis was rarely observed.
In some patients with bone metastases, hypercalcaemia was observed at the beginning of treatment.
Tamoxifen causes amenorrhea or irregularity of menstrual periods in premenopausal women, as well as the reversible occurrence of cystic ovarian tumors. With prolonged treatment with tamoxifen, changes in the endometrium, including hyperplasia, polyps, development of uterine fibroids and in isolated cases - endometrial cancer, uterine sarcoma, can occur.