Drug: figure popping one on bed (8)
I believe the answer is:
nicotine
'drug' is the definition.
(I know that Nicotine is a drug)
'figure popping one on bed' is the wordplay.
'figure' becomes 'nine' (a number of figure).
'popping' means one lot of letters goes inside another (inserted letters are consumed or \'popped\').
'one' becomes 'i' (Roman numeral).
'on' means one lot of letters go next to another.
'bed' becomes 'cot' (cot is a type of bed).
'i'+'cot'='icot'
'nine' enclosing 'icot' is 'NICOTINE'.
(Other definitions for nicotine that I've seen before include "Chief constituent of tobacco" , "Highly-addictive alkaloid" , "Tobacco element" , "Hooker" , "Poison that occurs in tobacco" .)