Prescription liquid is in addition to other liquid allowance.
When it comes to inhalers, though, that depends on who you're dealing with. They are classed as liquids, and they are of course on prescription, and DH usually puts them in a second plastic bag. But a few months ago a member of staff insisted he was only allowed one clear liquids bag and both his inhalers had to go in it. He managed (just) to force them in with the toiletries already in there, but she stood over him until he shut it properly and told him he'd have to ditch something if he couldn't. It's a grey area.
Watch out with the little bottles you decant things into as well. If they don't have 100ml or less stamped on them, they can be rejected, as a friend of mine found out recently to her cost.