@misc{9188,
  author = {Y. Vinogradova and C. Coupland and J. Hippisley-Cox},
  title = {Use of combined oral contraceptives and risk of venous thromboembolism: nested case-control studies using the QResearch and CPRD databases},
  year = {2015},
  journal = {Bmj},
  volume = {350},
  pages = {h2135},
  issn = {0959-8138},
  doi = {10.1136/bmj.h2135},
}