[matt_the_bass]

It’s very important to note that pressure plays a role in how quickly the body processes out the medicine. A dose might last 6 hours on land may last much less under pressure. One significant danger to this is a decongestant wearing off unexpectedly early while underwater, resulting in congestion a depth and preventing equalization upon ascent. This could result in a barotrauma often called “reverse squeeze”.

[hunter2_]

Definitely worth noting, but personally I've never had any discomfort during ascent even prior to using the decongestant, and based on some other comments here, that seems to be because our ears are better equipped to readily equalize when over pressurized than under... approximating a check valve, I suppose?

I use the generic (CVS brand) 12-hour extended release 120mg about an hour before diving, then two dives with a surface interval between, so I'm only relying on about 4 of those claimed 12 hours. I'm not sure the magnitude of the effect you warn of regarding accelerated processing, but there's a good margin to work with. There's also a 24hr formulation available.

[matt_the_bass]

I’ve done the same. But my point is the “specs” are not well documented and a novice may not have considered this factor.