A drug that will give you a heavenly body (8)
I believe the answer is:
asteroid
'a heavenly body' is the definition.
(I know that asteroid is a type of minor planet)
'a drug' is the wordplay.
'drug' becomes 'steroid' (type of drug).
'a'+'steroid'='ASTEROID'
'that will give you' acts as a link.
(Other definitions for asteroid that I've seen before include "Bits of rock that move around the heavens" , "Small heavenly body" , "Minor planet" , "way-out rock" , "circling rock" .)