Tasteless, if popular, drink one had (7)
I believe the answer is:
insipid
'tasteless' is the definition.
(similar in meaning)
'popular drink one had' is the wordplay.
'popular' becomes 'in' ('in' can mean trendy).
'drink' becomes 'sip' (sipping is a kind of drinking).
'one had' becomes 'Id' ('I'd' can mean 'one had').
'in'+'sip'+'id'='INSIPID'
'if' is the link.
(Other definitions for insipid that I've seen before include "Very weak" , "dry" , "Dull" , "Tasteless" , "flat" .)