Carrots are rich in carotenes, which are substances related to vitamin A. They're found in the orange pigments and are good for you, but, if you eat lots and lots of carrots, you can develop a yellowish or orange cast to your skin. It's mostly noticeable on the soles of your feet and the palms of your hands.
Benadryl is another decongestant safe for use in cats, although it is usually not as effective as chlortrimeton in treating congestion. Benadryl is generally more beneficial with treating snake bites, reactions to vaccinations, itching, and insect bites.
At the present time I think that thalidomide is not available to veterinarians in the United States, though. There is evidence to support the use of AZT (ziduvudine, Retrovir, Rx) in cats for severe stomatitis associated with FIV. The dosage that was used in one study was 5mg/kg given by subcutaneous injection twice daily (Hartman 1992) and cats treated with the medication improved compared to the control group.