Sildenafil (Generic) Cognitive Function Impact: What the Evidence Actually Shows

Does sildenafil have an approved cognitive use?

No. Viagra is sildenafil citrate tablets of 25, 50 and 100 mg, indicated for erectile dysfunction and first approved on 27 March 1998 [1][3]. Revatio tablets are 20 mg and are indicated for pulmonary arterial hypertension in adults to improve exercise ability and delay clinical worsening, and in children 1 to 17 years to improve exercise ability [2][4]. The Revatio label says the safety and efficacy of combining it with Viagra or another PDE5 inhibitor have not been studied, and tells patients not to take them together [4].

The usual erectile dysfunction dose is 50 mg about one hour before sexual activity, adjustable to 25 or 100 mg, no more than once a day [3].

What the labels record about the nervous system

The Viagra label lists insomnia, somnolence, abnormal dreams, depression, paresthesia and tremor among events reported in fewer than 2% of trial patients, with a causal relationship uncertain [3]. Dizziness was reported more often, by 3% to 4% of men on 25 to 100 mg versus 2% on placebo in fixed-dose trials [3]. The Revatio postmarketing section lists seizure and seizure recurrence [4].

Abnormal vision (mostly a color tinge, also increased light sensitivity or blurred vision) was reported by 1% on 25 mg, 2% on 50 mg and 11% on 100 mg versus 1% on placebo [3]. The Revatio label says sildenafil is only about 10-fold more potent against PDE5 than against PDE6 in the retina, and that this lower selectivity is thought to be the basis for color-vision changes at higher doses or plasma levels [4].

Blood pressure, older adults and nitrates

Single 100 mg doses lowered supine blood pressure in healthy volunteers by a mean maximum of about 8.4/5.5 mm Hg [3]. Nitrates in any form and riociguat are contraindicated [3][4], and after a dose of Viagra the label says it is unknown when nitrates can safely be given [3]. Exposure is about 84% higher in healthy men aged 65 and older, and the label says to consider a 25 mg starting dose in men over 65 [3].

What the pivotal trials measured

The erectile dysfunction trials measured erectile function and the success of intercourse attempts: in the 12-week flexible-dose study, 69% of attempts were successful on sildenafil versus 22% on placebo [5]. The SUPER-1 pulmonary arterial hypertension trial (278 patients, 12 weeks) measured six-minute walk distance, with placebo-corrected gains of 45 to 50 m across the 20, 40 and 80 mg three-times-daily doses [6]. Neither primary outcome was a memory or thinking test, so these results do not show that sildenafil protects memory or delays dementia.