Electrotherapy is an approach to treatment which still has a place in medical practice. Techniques such as deep brain stimulation and electro-convulsive therapy are two of the most highly medicalised applications of electrotherapy. Yet, as this paper argues, in the early twentieth century devices were marketed by companies to the general public, bypassing the medical profession. One such electrotherapy device was the "Rejuvenator". This was developed by Otto Overbeck, a British chemist who made his name as Scientific Director of a brewing firm in Grimsby, a provincial fishing town. Overbeck patented a number of modifications to brewing technologies during the first decade of the twentieth century, and later turned his attention to electrotherapy. He patented his Rejuvenator, which he claimed could be used to treat a vast variety of conditions, very widely from the 1920s onwards. The patents themselves were part of a broader marketing strategy, which included testimonies from practitioners and users, appeals to Overbeck’s scientific credentials, and claims of manufacturing integrity. Overbeck was able to pursue such strategies precisely because he was a chemist rather than a clinician, and therefore did not have to abide by professional codes of conduct which applied to other medical innovators. This paper argues that patents gave credibility to the Rejuvenator, and convinced potential purchasers that the device would work to treat a vast array of different illnesses and ailments. Overbeck’s goal was to legitimise his device, and to persuade potential consumers that it was a viable alternative to professional medical advice. In doing so, Overbeck incurred the wrath of both the British Medical Association and the Australian government when advertising and selling his device on a global scale. Using the Rejuvenator as a case study, this paper shows that there was a complex relationship between the marketing of medical devices, patents and electrotherapy in the early twentieth century.