Common uses Viagra is used to treat erection difficulties, such as erectile dysfunction (ED). Directions Viagra comes as a tablet containing 100 mg. sildenafil citrate, to take by mouth. For most men, the recommended dose is 50 mg. taken, as needed, approximately 1 hour before sexual activity. However, sildenafil citrate may be taken anywhere from 4 hours to 0.5 hour before sexual activity. Based on effectiveness and toleration, the dose may be increased to a maximum recommended dose of 100 mg or decreased to 25 mg. The maximum recommended dosing frequency is once per day. Precautions A starting dose of 25 mg. should be considered individuals of the age 65+ and in individuals with hepatic impairment or severe renal impairment. Given the extent of the interaction with patients receiving concomitant therapy with ritonavir, it is recommended not to exceed a maximum single dose of 25 mg. of Viagra in any 48 hour period. Sildenafil citrate potentiates the hypotensive effects of nitrates and its administration in patients who use nitric oxide donors or nitrates in any form is therefore contraindicated. Treatments for erectile dysfunction, including Viagra, should not be generally used in men for whom sexual activity is inadvisable because of their underlying cardiovascular status. Patients who have suffered a myocardial infarction, stroke, or life-threatening arrhythmia within the last 6 months, patients with resting hypotension or hypertension, patients with cardiac failure or coronary artery disease and patients with retinitis pigmentosa should use Viagra with great caution. The safety of Viagra is unknown in patients with bleeding disorders and patients with active peptic ulceration. Viagra should be used with caution by individuals with anatomical deformation of the penis and by individuals who have conditions which may predispose them to priapism. The safety and efficacy of combinations of Viagra with other treatments for erectile dysfunction have not been studied. Therefore, the use of such combinations is not recommended. Possible side effects The most frequently observed side effects of Viagra includes headache, flushing, dyspepsia and nasal congestion. Less frequent side effects include erections that will not go away and vision changes. In the event that an erection persists longer than 4 hours, seek immediate medical assistance. Other less frequent side effects include urinary tract infection, abnormal vision, diarrhea, dizziness and rash. If you notice other effects not listed above, contact your doctor. Overdose If overdose of Viagra is suspected, contact your local poison control center or emergency room immediately. Additional information Keep Viagra in a tightly closed container and out of reach of children. Store Viagra at room temperature and away from excess heat and moisture (not in the bathroom). Note The above information is intended to supplement, not substitute for, the expertise and judgment of your physician, or other healthcare professional. It should not be construed to indicate that use of Viagra is safe, appropriate, or effective for you. Consult your health care professional before you buy Viagra (Sildenafil Citrate).