One has three legs? That'll be the consequences of taking drugs (6)
I believe the answer is:
tripod
'legs? that'll be the consequences of taking drugs' is the definition.
I can't tell whether this definition defines the answer.
'one has three' is the wordplay.
'one' becomes 'pod' (I can't justify this - if you can you should give a lot more credence to this answer).
'has' says to put letters next to each other.
'three' becomes 'tri' (prefix meaning 'three').
'pod' after 'tri' is 'TRIPOD'.
Can you help me to learn more?
(Other definitions for tripod that I've seen before include "support called for" , "Something on three legs" , "Three-legged stand as for camera" , "Stand on three legs" , "Torpid (anag.)" .)