Caroline, just a thought about nattokinase. It is an enzyme, produced by adding the bacterium Bacillus natto to boiled soybeans.

Enzymes are proteins.

All of the comp/alt med sites that I can see sell it in a form to be taken by mouth.

If you are taking it by mouth that is fine - it will not harm you but will not help either.

That is because nattokinase, in just the same way as all of the other proteins in your food, will be broken down into its constituent amino acids by digestive enzymes in your gut. Amino acids can cross the gut wall into your blood - whole proteins can not.

A close analogy: people with Type 1 diabetes need a daily dose of insulin (which is a small protein) to stay alive - they get that dose by injection.

Taking insulin by mouth would be pointless because, (just the same as nattokinase), it would be broken down into its amino acids during digestion. Insulin can not cross the gut wall - that is why people with Type 1 diabetes do not get their insulin in oral form.