title: On call. I am a 71-year-old diabetic , and I've had trouble with my erections for seven or eight years. At first the problem was mild, but it's been getting worse. My doctor gave me a prescription for Viagra, but it didn't help. I tried two pills at once without any luck, but I did get a mild headache. Can I use three pills?
mesh_terms: D000368:Aged; D007172:Erectile Dysfunction / Q000188:drug therapy*; D006801:Humans; D008297:Male; D010726:Phosphodiesterase Inhibitors / Q000008:administration & dosage* / Q000009:adverse effects; D010879:Piperazines / Q000008:administration & dosage* / Q000009:adverse effects; D011687:Purines; D000068677:Sildenafil Citrate; D013450:Sulfones; D014665:Vasodilator Agents / Q000008:administration & dosage* / Q000009:adverse effects
chemical_list: D010726:Phosphodiesterase Inhibitors; D010879:Piperazines; D011687:Purines; D013450:Sulfones; D014665:Vasodilator Agents; D000068677:Sildenafil Citrate