I decided to follow up some more recent research into the side effects of
taking too much cinnamon and found the following excerpts:

Oral mucosal reactions to cinnamon-flavored chewing gum; oral leukoplakia
caused by cinnamon food allergy. Also:

The 1997 Commission E on Phytotherapy and Herbal Substances of the German
Federal Institute for Drugs recommends Cinnamon 'For loss of appetite,
dyspeptic complaints such as mild, spastic condition of the
gastrointestinal tract, bloating, flatulence.'

'Side Effects: Frequently, allergic reactions of skin and mucosa.'

'Daily Dosage: 2 - 4 g of bark; 0.05 - 0.2 g of essential oil; equivalent
preparations. Mode of Administration: Cut or ground bark for teas,
essential oil, as well as other galenical preparations for internal use.
Actions: Antibacterial; Fungistatic; Promotes motility.'

Other signs of acute cinnamon toxicity include facial flushing, shortness
of breath, tachycardia, dizziness, and abdominal pain. ...

There was a reference to 'cinnamon abuse in adolescents' but I was unable
to access the paper. I can only assume that they mistook it for nutmeg,
unless anyone else can explain this <g>

Having been intrigued by the research that Marilyn posted, I looked at
some earlier research and found one that might be of interest to those of
us who love lots of fat in our diets, and don't object to being compared
to smaller mammals ;-)

Anti-oxidant effects of cinnamon (Cinnamomum verum) bark and greater
cardamom (Amomum subulatum) seeds in rats fed high fat diet.

Indian J Exp Biol 1999 Mar;37(3):238-42    (ISSN: 0019-5189)
Dhuley JN
Pharmacology and Toxicology Division, Hindustan Antibiotics Limited,
Pimpri, Pune, India.

In order to gain insight into the antioxidant effect of cinnamon
(Cinnamomum verum; Lauraceae) and cardamom (Amomum subulatum;
Zingiberaceae) hepatic and cardiac antioxidant enzymes, glutathione (GSH)
content and lipid conjugated dienes were studied in rats fed high fat diet
along with cinnamon or cardamom. The antioxidant enzyme activities were
found to be significantly enhanced whereas GSH content was markedly
restored in rats fed a fat diet with spices. In addition, these spices
partially counteracted increase in lipid conjugated dienes and
hydroperoxides, the primary products of lipid peroxidation. Thus, it
appears that these spices exert antioxidant protection through their
ability to activate the antioxidant enzymes.

Cheers,

Persephone (who loves cinnamon in mulled wine)