Pharmaceutical companies are known to be among the most profitable companies in the world. Proceedings of legal cases and published research provide insights into the nature of the influence of drug companies on research and publication practices relating to the drugs they manufacture, on marketing disguised as "education" and on doctors who prescribe their drugs. The influence of drug companies extends further to sponsorship of opinion leaders who promote their drugs and groups that produce clinical guidelines. More rigorous regulation of the relationship between the pharmaceutical industry and medicine is required.