After graduation, Black took a teaching job in Singapore for three years. He moved to London in 1950. Later in 1950, he returned to Scotland. He joined the University of Glasgow (Veterinarian School). There that he became interesteed in how adrenaline affects the human heart. He was mainly interesting in how it affected people with angina. He found the effects of adrenaline did not help. He joined ICI Pharmaceuticals in 1958. He worked with the company until 1964. During this time, he created propranolol, which became the world's best-selling drug. While at ICI, Black developed a new way of doing research. Before this, drug molecules would be created and then tested to find in what ways the molecules could be used as medicine. Black chose to pick a medical use and then try to create the molecules for that medicine. The discovery of propranolol was said to be the greatest discovery in the treatment of heart disease since the discovery of digitalis.