Professor Johnston’s research interests are in drug use and abuse, drug quality, clinical trial design and statistical data analysis, modelling pharmacokinetics and pharmacodynamics, and in the optimal use of drugs with particular reference to immunosuppresive, cardiovascular, analgesic and anti-cancer drugs.

He has over 300 publications in the peer reviewed journals indexed by PubMed. His current H-Index is 59 (in the top 20th percentile of the more than 40 professors in the William Harvey Research institute).

He is a Fellow of the British Pharmacological Society, the Royal College of Pathologists, the Royal Society of Medicine, the Royal Statistical Society and an honorary member of the Faculty of Pharmaceutical Medicine. He is a Chartered Scientist, a European Registered Toxicologist, and a state registered Clinical Scientist. He holds following university degrees - Bachelor of Science (with honours) in biochemistry (toxicology), Bachelor of Arts (with honours) in mathematics and statistics, Master of Science in applied statistics and Doctor of Philosophy in pharmacology.