Needle a woman at port in Algeria used for drug (9)

'for drug' is the definition.
The definition suggests a singular noun which matches the answer.

'needle a woman at port in algeria' is the wordplay.
I cannot really see how this works, but
'a' could be 'an' and 'an' is found in the answer.
'woman' could be 'di' (short for Diana) and 'di' is present in the answer.
This explanation may well be incorrect...

'used' is the link.

Can you help me to learn more?