The most common adverse effects are associated with its vasodilator action and often diminish on continued therapy. They include dizziness, flushing, headache, hypotension, peripheral edema, tachycardia and palpitations. Nausea and other gastrointestinal disturbances, increased micturition frequency, lethargy, eye pain and mental depression have also occurred. A paradoxical increase in ischemic chest pain may occur at the start of treatment and in a few patients excessive fall in blood pressure has led to cerebral or myocardial ischemia or transient blindness.
There have been reports of rashes (including erythema multiforme), fever, and abnormalities in liver function, including cholestasis, due to hypersensitivity reactions. Gingival hyperplasia, myalgia, tremor and impotence have been reported.