Are antihistamines good for cough-variant asthma?

Depends: Antihistamines tend to dry secretions permitting them to thicken & become harder to bring up naturally or with a cough. Some do this more than others. Many of the newer 1/day antihistamines seem less likely to do so. This is something you can try for a while & see how it works for you. I find it a benefit for many with this condition.