The most frequently reported undesirable effects are due to tamoxifen's anti-oestrogenic effect and include hot flushes, abnormal vaginal bleeding, including menstrual irregularities, vaginal discharge and pruritus vulvae. Other effects include fluid retention, nausea, vomiting and less frequently tumour flare, light-headedness, skin rash and alopecia, tiredness and headache.
In males, impotence or loss of libido.
Rarely anorexia, impairment of taste sense, obstipation, diarrhoea, convulsions of legs, depressions and alopecia or intensified hair growth.
Menstruation may be suppressed in premenopausal women.
Reversible cystic ovarian swellings have occasionally been observed in premenopausal women receiving tamoxifen.
A small number of patients with bony metastases have developed hypercalcaemia on initiation of therapy. An initial increase of bone and tumor pain and increased erythema around skin lesions, which can be taken as an indicator for response on treatment, are possible. Enlargement of existing skin lesions or appearance of new ones is possible.
More serious undesirable effects include: leukopenia and/or thrombocytopenia (platelet counts usually between 80,000 and 90,000/mm3) and very rarely neutropenia and pancytopenia.
Tamoxifen has been associated with an increased risk of the development of proliferative endometrial changes, as the development of endometrial hyperplasia, polyps, endometriosis and in rare cases endometrial cancer. The risk of endometrial cancer increases with duration of therapy and have been estimated to be 2 to 3-fold greater in tamoxifen treated patients than in untreated women. But the clinical benefit in women with breast cancer outweighs any increased risk of endometrial neoplasm.
Ophthalmological disturbances including decreased visual acuity, corneal opacities, cataracts and retinopathy have been described. Probably these effects are depending on the dosage and the duration of treatment and may show improvement once Tamoxifen is discontinued.
Commonly thrombosis and very rarely embolism (pulmonary) have been described.
The concomitant administration of tamoxifen and cytotoxic agents may increase the risk of thromboembolic events.
Tamoxifen has an effect on serum lipid profiles, hypertriglyceridemia has been reported very rarely, partly with pancreatitis.
Tamoxifen has been associated with increases in hepatic enzymes and on rare occasions with more severe hepatic abnormalities including fatty liver, cholestasis and hepatitis.
Hypersensitivity reactions including skin rashes, angioedema, erythema multiforme, Stevens-Johnson Syndrome and bullous pemphigoids may rarely appear.
Most of these side-effects are reversible and can often be treated by dose-reduction.