title: Do I need to see a doctor to get a prescription for Viagra? I've seen ads offering Viagra direct by mail.
mesh_terms: D011307:Drug Prescriptions; D007172:Erectile Dysfunction / Q000188:drug therapy* / Q000209:etiology; D006801:Humans; D008297:Male; D010726:Phosphodiesterase Inhibitors / Q000627:therapeutic use*; D010879:Piperazines / Q000627:therapeutic use*; D011687:Purines; D000068677:Sildenafil Citrate; D013450:Sulfones
chemical_list: D010726:Phosphodiesterase Inhibitors; D010879:Piperazines; D011687:Purines; D013450:Sulfones; D000068677:Sildenafil Citrate