He is specializing in anaesthetics at medical school and knows all about different anesthetic drugs.

anaesthetics 是名词，由前缀 an-（表示"无、不"）和词根 aesthesia（感觉）加上后缀 -ics（表示"学科"）组成，字面意思是"无感觉的学科"，即"麻醉学"。在英式英语中常用 anaesthetics，而在美式英语中对应词是 anesthetics。