The safety of sildenafil has been well demonstrated in its long history of use. In a review study looking across >14,000 men taking sildenafil for ED, 2-3% experienced side effects that required stopping of the medication, while <1% of men experienced serious side effects.
Also, in another study specifically looking at a subset of 60 Singaporean men with ED, sildenafil was shown to be well-tolerated – all side effects were transient/mild and did not lead to treatment withdrawal.
In short, safety concerns on sildenafil are heavily outweighed by the positive impact it can bring on the quality of life of men suffering from ED.