title: Viagra and erections: do the benefits persist?
mesh_terms: D004361:Drug Tolerance; D007172:Erectile Dysfunction / Q000188:drug therapy* / Q000503:physiopathology; D006801:Humans; D008297:Male; D010410:Penile Erection / Q000502:physiology; D010413:Penis / Q000098:blood supply*; D010726:Phosphodiesterase Inhibitors / Q000009:adverse effects / Q000627:therapeutic use*; D010879:Piperazines / Q000008:administration & dosage / Q000627:therapeutic use*; D011687:Purines; D000068677:Sildenafil Citrate; D013450:Sulfones; D014665:Vasodilator Agents / Q000008:administration & dosage / Q000627:therapeutic use*
chemical_list: D010726:Phosphodiesterase Inhibitors; D010879:Piperazines; D011687:Purines; D013450:Sulfones; D014665:Vasodilator Agents; D000068677:Sildenafil Citrate