In 2021, GW Pharmaceuticals plc was sold for $7.2 billion (£5.2 billion), but Dr Geoffrey Guy started it with just a licence from the UK Home Office and his personal cheque book. A Worthwhile Medicine tells the story of how and why he persuaded reluctant health regulators, sceptical investors and a conservative medical establishment that cannabis really could form the basis for a modern pharmaceutical - which he defines as 'a worthwhile medicine that can make money'. He had built up one publicly quoted pharmaceutical company only to have to step down from the top job after a failed attempt to float on the UK stock market. Undeterred, he started another venture after hearing heartrending tales of how multiple sclerosis sufferers were being denied symptom-relief because cannabis was a prohibited drug. He believed the answer was not to change the law and decriminalise recreational drugs but to create a licensed medicine from cannabis that doctors could prescribe safely for their patients. Looking to the future, Dr Guy has established a foundation to explore the exciting new area of quantum biology - the science of sub-atomic particles - which is completely changing our understanding of the ways in which all life functions.