Tobacco was a plant that was often burnt and inhaled. It was used in cigarettes, cigars and smoking pipes. The First Doctor once smoked tobacco from a pipe. (TV: "The Cave of Skulls") Samuel Pike's smuggling ring often imported and exported tobacco. (TV: The Smugglers)
The Fourth Doctor told George Litefoot that there was no tobacco where Leela came from when she did not recognise what a smoking pipe was. Litefoot concluded it sounded healthy but exceedingly dull. (TV: The Talons of Weng-Chiang)
In the 21st century, cigarette boxes advertised that "SMOKING IS BAD." (TV: Out of Time)
Tobacco became rare in the aftermath of the 22nd century Dalek invasion. (PROSE: Legacy of the Daleks)