Hi wassermann:
People frequently, and very understandably, get confused when they talk about medications- especially over-the-counter (OTC) medications which I'm convinced the manufacturers intentionally make confusing (grin). For example, there is no medicine called "Sudafed". There is a medicine called "Sudafed 12 Hour Tablets", and one called "Sudafed Sinus Headache Tablets", and one called "Sudafed Severe Cold Formula Tablets", and at least 11 other preparations with "Sudafed" in their name, but there is no "Sudafed". I think that it is
VERY important that people are clear on
exactly what they are talking about before they give advice on a medication or discuss its effects or side effects. (Regular board readers will probably tell you it is a pet peeve of mine.)
There is also no blanket rule that you can't take prescription (or OTC) medicines when diving. Many are safe and effective. Often the benefits of a medicine outweigh the potential risks. However there
is a general recommendation that you not dive when you are in a physical or mental state that would make diving less than acceptably safe. That might include diving when sick, dehydrated, hung over, or on medications that might have effects or side effects that would interfere with diving.
When divers say "Sudafed" they generally mean one of the active ingredients in the "Sudafed" family of OTC meds called
pseudoephedrine. Pseudoephedrine belongs to a class of chemicals called
sympathomimetic amines. It has effects and side effects similar to amphetamines, ephedrine, and adrenaline. It is
not an antihistamine nor does it really excite oxygen. Divers use pseudoephedrine because it shrinks the mucosal linings of the nose, sinus passages, and eustachion tubes and helps with equalization of air spaces. Since it's in the "adrenaline family" it does not (usually) make you sleepy like antihistamines can. The intended "effect" of pseudoephedrine is a beneficial one for divers and it lacks (or has less of) some of the
side effects of other medicines that might have similar effects, so it is probably the most often recommended decongestant for diving. At least one study has looked at the effects of pseudoephedrine in diving and found it safe in the environment they studied.*
But remember, pseudoephedrine is a sympathomimetic amine in the "adrenaline family" and will have effects similar to adrenaline. It is not really an "oxygen exciter", but I guess you could call it a "nerve exciter". At increased partial pressures, oxygen can also be a "nerve exciter" so there is the
theoretical concern that the nerve excitement might be additive. So some recommend that pseudoephedrine not be used with nitrox where the risk of oxygen toxicity is greater.
Since pseudoephedrine is a "nerve exciter" it can also cause nervousness, sleeplessness, dizziness, rapid heartbeat, irregular heartbeat, and tremor- all untoward effects when diving. It should not be taken by people with high blood pressure, heart disease, diabetes, glaucoma, hperthyroidism, kidney disease, or prostate enlargement without the advice of a physician.
But, hey, I sometimes take it when I dive when I think the benefits of the effects outweigh the risks of the side effects.
HTH,
Bill
*
Study Link
NOTE: This study looked at the effects of pseudoephedrine on air at 3ATA (66 fsw) in a dry chamber.