Hi Lindalea,
There are several forms of Sudal, all designed to treat the symptoms of colds & allergies. All contain both guaifenesin & pseudoephedrine. The former drug is intended to clear mucous & congestion (some questions about its effectiveness), while the latter is intended to relieve nasal congestion (effective).
As regards diving, guaifenesin should pose no problem. Taken as directed in OTC preparations, it's pretty benign stuff
The side effects of pseudoephedrine can include nervousness, restlessness, dizziness, difficulty sleeping & upset stomach. Luckily, when the drug is taken as directed in OTC preparations these are not terribly common & often pass rather quickly with usage. Very rarely, difficulty breathing, fast or irregular heartbeat, muscle weakness, tremors & hallucinations can occur. Given these possibilities, one would be well advised to give medications containing pseudoephedrine a trial run before engaging in any activity for which it could conceivably pose a risk.
I know of only one study that has examined the effects of pseudoephedrine on scuba diving & it reported nothing of concern. A number of divers take pseudoephedrine containing drugs like the various Sudafed compounds, a few seem to report any significant problem.
The input from the allergist should be useful even though s/he is not a diving doc. You may also inquire of DAN
http://www.diversalertnetwork.org/medical/ if you are so disposed.
Of course, your daughter should inform her OW instructor of all medications she is taking.
This is educational only and does not constitute or imply a doctor-patient relationship. It is not medical advice to you or any other individual, and should not be construed as such.
Best regards.
DocVikingo
