Do not stop taking sildenafil without talking to your doctor. If you experience chest pain, dizziness, or nausea during sexual activity, call your doctor immediately and avoid sexual activity until your doctor tells you otherwise. Tell your doctor if sildenafil is not working well or if you are experiencing side effects. If you prefer, you may contact the U. Take sildenafil exactly as directed. The most common side effects of VIAGRA: headache; flushing; upset stomach; abnormal vision, such as changes in color vision such as having a blue color tinge and blurred vision; stuffy or runny nose; back pain; muscle pain; nausea; dizziness; rash. Some medications should not be taken with sildenafil.Ad享精選品牌天然健康產品鉅惠，請在結賬時使用折扣碼 SPREE11。. 不要錯過 iHerb 全場特惠！下單即享 75 折！Brands: California Gold Nutrition, Doctor’s Best, Jarrow Formulas, Nature’s Way. Currently, there are no over the counter alternatives to Viagra available. Viagra (sildenafil) is a prescription medication, meaning it’s not available over the counter from your local. Sildenafil is in a class of medications called phosphodiesterase (PDE) inhibitors. Sildenafil treats erectile dysfunction by increasing blood flow to the penis during sexual stimulation. This increased blood flow can cause an erection. Sildenafil treats PAH by relaxing the blood vessels in the lungs to allow blood to flow easily.