Garment causes overheating and wearers regularly develop thirst (10)
I believe the answer is:
sweatshirt
'garment' is the definition.
(sweatshirt is a kind of garment)
'wearers regularly develop thirst' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'develop' indicates anagramming the letters.
'thirst' becomes 'tshirt' (I can't justify this - if you can you should give a lot more credence to this answer).
The alternate letters of 'wearers' are 'waes'.
'waes' anagrammed gives 'swea'.
'swea'+'tshirt'='SWEATSHIRT'
'causes overheating and' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for sweatshirt that I've seen before include "leisurewear" , "Long-sleeved top worn by athletes" , "casual gear" , "Long-sleeved, knitted cotton sweater" .)