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Oral contraceptives are meant only for women, to prevent ovulation or implantation and hence avoid pregnancy. They are not meant for men, and hence no such studies have been conducted to see the effects in men.
But use of estrogen-containing drugs, steroids, ulcer medications such as cimetidine, some antibiotics (tetracycline, ampicillin, etc.), anti-fungal medications and antidepressants can cause abnormally high estrogen levels in men. Such men can have enlargement of their breasts. The degree of enlargement varies, but is proportional to the dosage and the duration (in months), upto which the medication is used.
Other possible effects of increased estrogen levels in men include - (higher voice, loss of body hair, decrease in muscle mass, increase in fatty tissue, prostate enlargement, change in sex drive, difficulty in losing weight, etc.