I take Viagra when I walk in the Highlands, and it was after overcoming the 3500 mark. I prefer sildenafil citrate 100mg. The thing is that at the level of the sea side effects of this product is poured out for me a headache, the effect was very good and long lasting, but my lady seriously scared for me, after two days I walked along the wall. But in the mountains (altitude 3900) generic viagra has helped deal with mountain sickness. I heard that carried out some tests on cyclists group, and so, those that were weaker all showed the highest level of endurance at high altitudes. It may be a side effect is somehow connected with this?