Inclusion Criteria

DISEASE CHARACTERISTICS:

- Women with a history of breast cancer (currently without malignant disease)

- Bothersome hot flashes (defined by their occurrence ≥ 28 times per week and of
sufficient severity to make the patient desire therapeutic intervention)

- Presence of hot flashes for ≥ 30 days prior to study registration

- Willingness to provide the biologic specimens as required by the protocol

- Hormone receptor status not specified

PATIENT CHARACTERISTICS:

- Women who are postmenopausal as defined by absence of a period in the past 12 months
or bilateral oophorectomy

- Women with at least one ovary but without a uterus should be deemed
postmenopausal by either age over 55 or a combination of estrogen within a
postmenopausal range (per local lab) and FSH over 40 mIU/mL

- No women of childbearing potential or who are premenopausal

- Creatinine clearance > 30 mL/min

- Ability to complete questionnaire(s) by themselves or with assistance

- ECOG performance status 0 or 1

- No history of allergic or other adverse reaction to magnesium

- No diabetes

- No patients with conditions that are implicated in decreased absorption of magnesium
(e.g., Crohn disease, ETOH abuse)

- No patients who have diarrhea where magnesium might make it worse (per provider
discretion)

PRIOR CONCURRENT THERAPY:

- None of the following current (≤ 28 days prior to registration) or planned therapies
(tamoxifen, raloxifene, or aromatase inhibitors are allowed, but the patient must
have been on a constant dose for ≥ 28 days and must not be expected to stop the
medication during the study period):

- Antineoplastic chemotherapy (trastuzumab or lapatinib are allowed)

- Androgens

- Estrogens (any delivery route)

- Progestational agents

- No prior use of magnesium for hot flashes

- No current or planned use of gabapentin (for any reasons) or antidepressants (for any
reasons) or other agents for treating hot flashes (except stable dose of vitamin E is
allowed as long as it was started > 30 days prior to study registration and are to be
continued through the study period; soy is allowed, if it is planned to be continued
at the same dose during the study period)

- No current use of magnesium for any indication (except one standard multiple vitamin
dose is allowed per day)

- Not taking diuretics, corticosteroids, bile acid sequestrants, and other prescription
and over-the-counter medications that may affect magnesium levels

- No current (≤ 7 days prior to registration) or planned use of other non-drug
therapies for managing hot flashes, such as acupuncture or yoga (use of these
therapies for other reasons is allowed)