Summary
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Health benefits of nattokinase supplements:
Nattokinase supplements have been promoted to reduce the risk of blood clots and reduce blood pressure. However, the evidence for these effects in people remains preliminary: No study has definitively shown a reduction in clots in people from using nattokinase, although a reduction in blood clotting factors has been demonstrated, and nattokinase causes only a small reduction blood pressure. (See "What It Does") -
How to choose a nattokinase supplement:
When choosing a nattokinase supplement, it is important to look for one which lists its enzyme activity, which will be in FU (fibrin degradation or fibrinolytic units). Listing just the amount of enzyme in milligrams doesn't tell you enough, since not all nattokinase is equally active. You'll want a product providing at least 1,000 FU per pill or unit (see "What It Is"). Also, check that ConsumerLab.com or another reputable independent 3rd party has verified the enzyme activity, as not all products provide the activity they list (see "What CL Found"). 
Best value for nattokinase:
Products which ConsumerLab.com found to contain their listed nattokinase enzyme activity are indicated as Approved in the 3rd column of the Results Table below. Among those, several provide the best value (i.e., greatest enzyme activity at lowest cost) -- see Top Picks.-
Nattokinase safety and side effects:
Short term use of nattokinase supplements is generally well-tolerated but people who are taking medications such as blood-thinners or blood-pressure lowering medication should use them only with caution (See "Concerns and Cautions"). Nattokinase may also increase bleeding in the event of trauma or during and after surgery. Many nattokinase supplements contain soy and should not be used by people with an allergy to soy. See the last column of the Results Table to find out which claim soy.
