Mammoplasia is the normal or spontaneous enlargement of the breasts.[1] Mammoplasia occurs normally during puberty and pregnancy in women, as well as during certain periods of the menstrual cycle (as in premenstrual water retention).[2][3][4] When it occurs in males, it is called gynecomastia and is considered to be pathological.[4] When it occurs in females and is extremely excessive, it is called macromastia (also known as gigantomastia or breast hypertrophy) and is similarly considered to be pathological.[5][6][7] Mammoplasia may be due to breast engorgement, which is temporary enlargement of the breasts caused by the production and storage of breast milk in association with lactation and/or galactorrhea (excessive or inappropriate production of milk).[8] Mastodynia (breast tenderness/pain) frequently co-occurs with mammoplasia.[9][10]

Mammoplasia can be an effect or side effect of various drugs, including estrogens,[2][11] antiandrogens such as spironolactone,[12] cyproterone acetate,[13] bicalutamide,[14][15] and finasteride,[16][17] growth hormone,[18][19] and drugs that elevate prolactin levels such as D2 receptor antagonists like antipsychotics (e.g., risperidone), metoclopramide, and domperidone[20][21] and certain antidepressants like selective serotonin reuptake inhibitors (SSRIs) and tricyclic antidepressants (TCAs).[21][22][23] The risk appears to be less with serotonin-norepinephrine reuptake inhibitors (SNRIs) like venlafaxine.[24] The "atypical" antidepressants mirtazapine and bupropion do not increase prolactin levels (bupropion may actually decrease prolactin levels), and hence there may be no risk with these agents.[20] Other drugs that have been associated with mammoplasia include D-penicillamine, bucillamine, neothetazone (neotizide/thiacetazone), indinavir, cyclosporine, marijuana, and cimetidine.[6][25]

A 1997 study found an association between the SSRIs and mammoplasia in 23 (39%) of its 59 female participants.[24] Studies have also found associations between SSRIs and galactorrhea.[22][26][27][28] These side effects seem to be due to hyperprolactinemia (elevated prolactin levels) induced by these drugs, an effect that appears to be caused by serotonin-mediated inhibition of tuberoinfundibular dopaminergic neurons that inhibit prolactin secretion.[24][26][27] It is noteworthy that the mammoplasia these drugs can cause has been found to be highly correlated with concomitant weight gain (in the 1997 study, 83% of those who experienced weight gain also experienced mammoplasia, while only 30% of those who did not experience weight gain experienced mammoplasia).[24] The mammoplasia associated with SSRIs is reported to be reversible with drug discontinuation.[28] SSRIs have notably been associated with a modestly increased risk of breast cancer.[29] This is in accordance with the fact that higher prolactin levels have been associated with increased breast cancer risk.