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.
Metronidazole is widely used to treat infections of Giardia in dogs, cats, and other companion animals, although it does not reliably clear infection with this organism and is being supplanted by fenbendazole for this purpose in dogs and cats.