Decongestants and DCS: No Link, So Far

Many divers use decongestants occasionally or regularly to prevent or treat congestion of the ears and sinuses during scuba diving. The more popular of these drugs include agents that stimulate the sympathetic nervous system ("sympathomimetics"), such as pseudoephedrine (e.g., Sudafed Congestion), phenylephrine (e.g., Sudafed PE) and oxymetazoline (e.g., Afrin Original) that work by reducing swelling in affected membranes. An association between using these drugs and decompression sickness has been theorized for some time, but until very recently, not subjected to rigorous research.

The first study to analyze a possible relationship between these medications and DCS was a Ph.D. dissertation completed last year by Richard Smerz, formerly the medical director of the University of Hawaii's hyperbaric treatment center. This was based on a sample of recreational divers evaluated for diving-related problems at the center between 1983 and 2010. It showed that while dehydration, repetitive diving, and violation of dive profiles were statistically significant contributors for the development of DCS, sympathomimetic decongestant use was not.

However, this does not mean that sympathomimetic decongestant use by a diver is without implications. Not only do they cause dizziness and drowsiness in some users, anecdotal reports from Divers Alert Network suggest that taking pseudoephedrine prior to diving while breathing pure oxygen increases the risk for oxygen toxicity in the central nervous system. Research has shown that high doses accelerate the onset of "ox-tox" seizures in rats breathing hyperoxic mixes. In his dissertation, Smerz concluded, "Extrapolating our findings to humans, we conclude that the recommended daily dose of pseudoephedrine should not be abused prior to diving with oxygen-enriched gas mixes or pure oxygen."

On balance, sympathomimetic decongestants appear to pose minimal risk to divers who use them only as directed, and tolerate them well. Still, divers using them would be prudent to go easy on nitrox mixes and otherwise keep their oxygen partial-pressure to conservative levels.

- - Doc Vikingo