Patients should be advised to report immediately any deterioration in exercise tolerance. Treatment should be discontinued in patients who develop new, unexplained symptoms of dyspnea, angina pectoris, syncope or lower extremity edema. The etiology of these valvulopathies has not been established and their course in individuals after the drugs are stopped is not known. Tolerance to the anorectic effect usually develops within a few weeks. Concomitant use of alcohol with phentermine HCl may result in an adverse drug interaction.
Caution is to be exercised in prescribing phentermine HCl for patients with even mild hypertension.
Insulin requirements in diabetes mellitus may be altered in association with the use of phentermine HCl and the concomitant dietary regimen. Phentermine HCl may decrease the hypotensive effect of guanethidine. The least amount feasible should be prescribed or dispensed at one time in order to minimize the possibility of overdosage. Studies have not been performed with phentermine HCl to determine the potential for carcinogenesis, mutagenesis, or impairment of fertility. It is also not known whether phentermine HCl can cause fetal harm when administered to a pregnant woman or can affect reproductive capacity.