I use Claritin. It is definitely non-drowsy and now comes in a 12 or 24 hour dosage. I just can't afford to cancel pool and sea sessions if I'm stopped up. It definitely works for me.
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According to my otolaryngeologist, I have extremely narrow eustacean tubes. This makes equalizing a very slow, and sometimes painful, experience, especially on the second and later dives of the day. If I get ANY pain, I am certain to develop hyperbaric trauma and lose 80% of my hearing within a few days. This condition lasts from 2-4 weeks.
The Doc recommended Afrin: two snorts in each nostril before my first dive of the day and one snort/nostril on subsequent dives. I sill wind up with HBT to some degree, because I tend to hurry the equalization process. However, without the Afrin I couldn't dive at all.
I'll use Claritin D once in awhile when slightly congested, but if I have a cold, runny nose, or serious congestion, I'll sit out diving that day (or days). For whatever reason, sometimes I get slight congested for a couple of days after flying, and this is the exact situation where I don't hesitate to take a 12 hour Claritin D.
I read a few years ago on DAN's website that using Allegra and diving nitrox was contraindicated, so although I like Allegra D, I stick to Claritin D for safety.