A bottle of nattokinase says 50 mg. Another says 2,000 FU. A third says 4,000 FU. Which one contains more enzyme? The first number describes weight. The others describe activity in a laboratory test. You can compare labeled activity once you know whether each number belongs to one capsule, one softgel, or an entire serving. You cannot convert an arbitrary weight of nattokinase to FU without the activity specification for that material.
Here is the surprise in three real labels. Allergy Research Group’s 50 mg capsules and its 100 mg softgels both supply 2,000 FU per labeled serving. One serving takes two capsules or one softgel, respectively. Arthur Andrew Medical’s Nattovena lists 4,000 FU in one capsule. That is a meaningful difference for reading the packages. It does not tell you which would be appropriate for a person or which would improve a health outcome.
What a fibrinolytic unit measures
Nattokinase is an enzyme associated with the production of natto, the Japanese food made by fermenting soybeans. Enzymes can be described by weighing a preparation or by measuring how it performs under specified test conditions. FU stands for fibrinolytic units. The assay measures activity involving fibrin, a protein involved in clot formation. A finished supplement panel reports the activity the manufacturer assigns to the product under those conditions. Memorial Sloan Kettering’s nattokinase overview
Think of how a baker describes yeast. You can weigh two packets to see how much material each contains. A separate test would tell you how the yeast behaves in a particular recipe. For an enzyme supplement, the gap between a laboratory measurement and its effects in a person is even more important. The label does not measure how much enzyme will reach a target in your body, how your other medicines affect the outcome, or whether a clinical event becomes less likely.
This explains why “50 mg versus 4,000 FU” is an unfinished comparison. If both weight and activity are disclosed for a specific preparation, you can calculate their relationship on that label. You cannot carry the ratio over to every nattokinase product. Manufacturing, formulation, and the details of the activity claim matter. When the activity line is missing, ask the manufacturer for the specification per full serving instead of using a conversion you found for another brand.
Three bottles, two different serving sizes
| Product | One full serving | Nattokinase material on that serving | Activity per serving |
|---|---|---|---|
| Arthur Andrew Medical Nattovena | 1 capsule | Weight not stated on panel reviewed | 4,000 FU |
| Allergy Research Group NSK-SD 100 mg | 1 softgel | 100 mg | 2,000 FU |
| Allergy Research Group NSK-SD 50 mg | 2 capsules | 100 mg total | 2,000 FU |
Arthur Andrew Medical Nattovena puts the activity number directly on the Supplement Facts panel. The package we reviewed lists one capsule per serving and 4,000 FU. There is no need to invent a milligram figure to compare that activity with another item. If weight matters for a particular professional recommendation, the missing measurement remains a question for the manufacturer. Arthur Andrew Medical’s product information
Allergy Research Group Nattokinase 100 mg softgels list 100 mg and 2,000 FU together in one softgel. Both numbers refer to the same ingredient in the same serving. They are not two amounts of material that should be added together. The physical format matters too. A softgel can have a different shell and other ingredients than a vegetarian capsule. Compare the full ingredients when an allergy or dietary restriction drives your choice. Manufacturer’s 100 mg softgel
Allergy Research Group Nattokinase 50 mg capsules are a good example of a product name that uses the amount per individual capsule. The full two-capsule panel lists 100 mg and 2,000 FU. Dividing the serving by two yields a nominal 50 mg and 1,000 FU per capsule. That arithmetic clarifies a product name. It does not provide a personal dosing instruction or make a half serving appropriate. Manufacturer’s 50 mg capsule
A practical way to compare two labels in a store
Start by covering the large number on the front with your thumb and reading the top of the back panel. Say the serving size aloud. Then put the activity figure and its units next to that serving. If you write “2 capsules = 2,000 FU” on one line and “1 softgel = 2,000 FU” on another, the two bottles become much easier to compare. You can now see why the different front-label milligrams did not imply different activity per full serving.
Next, compare package counts. Ninety of the 50 mg capsules give 45 full two-capsule servings. Sixty of the 100 mg softgels give 60 full one-softgel servings. Someone looking only at “90 versus 60” might buy the first bottle expecting it to last longer. What counts as a day’s supply depends on the actual directions and any professional advice. What counts as a complete labeled serving can be determined immediately from the panel.
Finally, check the product identity when reordering. “NSK-SD” appears on more than one Allergy Research Group bottle. A search result that preserves the branded ingredient but drops the strength, shell and count can lead you to a different item. Keep a photo of the old panel or save the specific product link. It is easier to resolve a changed label with both versions in front of you than with a remembered number and a similar-looking cap.
If you are comparing two listings for the same apparent product, check the spelling of the manufacturer’s name and the full bottle count before comparing prices. A store may show a low starting price for its smallest size while displaying a picture of the largest bottle. Select the variant first. Then write the number of complete servings beside that variant’s price. This prevents a common error in online shopping, where the price for one package ends up divided by the count for another.
What the price comparison can and cannot answer
We checked RCW’s one-time U.S. item prices on November 2, 2026. The 90-count Nattovena bottle was $39.99, the 60-count Allergy Research Group softgel bottle was $44.09, and the 90-count Allergy Research Group 50 mg capsule bottle was $62.39. Dividing by full labeled servings gives approximately $0.44, $0.73, and $1.39 per serving, respectively. The calculation excludes shipping, tax and any discount applied at checkout.
The serving comparison is useful for a shopping budget, but the activity per serving differs. To compare price for the same activity on paper, divide the price by total labeled activity in the bottle, then multiply by a convenient unit such as 1,000 FU. The 90-count Nattovena example contains 360,000 labeled FU in total. The 60-softgel example contains 120,000 FU. The 90-count 50 mg capsule example contains 90,000 FU. The calculation yields about $0.11, $0.37 and $0.69 per 1,000 labeled FU.
Here is the reason to stop the calculation there. A lower price per activity unit does not establish a lower price per health benefit. There is no line on any of these panels describing a guaranteed reduction in a person’s cardiovascular risk. If a clinician has advised against nattokinase in your situation, a cheaper bottle or a lower number on the front does not change that advice. If you compare another package size, repeat the arithmetic using its own price and count.
How a human study changes the meaning of the numbers
One randomized, double-blind trial enrolled 265 adults without clinical cardiovascular disease and compared nattokinase with a matching placebo. Researchers followed participants for a median of three years and measured changes in carotid artery wall thickness and stiffness. They found no statistically significant difference between groups on those measures. The study used a preparation providing 2,000 FU. That number describes the research protocol, not a recommendation for the reader. Randomized nattokinase prevention study
Notice how different that question is from the one an activity assay answers. A laboratory can describe fibrin breakdown in a test system. A prevention trial asks what happens to specified outcomes over time in people who take a particular preparation. The trial result does not mean the panel’s activity claim is wrong. It means that the activity number cannot be treated as evidence that the intervention achieved the studied clinical objective.
Likewise, the negative finding in that group does not automatically establish the outcome at a different strength, for someone with a different medical history, or in combination with medication. Those alternatives would need evidence of their own. A graph of 4,000 versus 2,000 FU is a graph of what the bottles declare. Looking at the taller bar and predicting twice the clinical benefit would add information that no one measured.
When the medication question comes first
Nattokinase can pose a bleeding concern, particularly alongside anticoagulants or antiplatelet medicines. If you take warfarin, aspirin, or another medicine affecting clotting, speak with the prescribing clinician before considering a nattokinase product. Tell them about the exact supplement and its labeled activity. If you are preparing for surgery, include supplements when the clinical team asks for your medication list. Memorial Sloan Kettering safety information
Never replace a prescribed anticoagulant with nattokinase or use a supplement to treat a suspected blood clot. A plan to change an anticoagulant belongs with the prescriber who knows why you take it. A concern about a possible clot needs medical attention. Looking for the largest FU figure is the wrong next step in either situation. The assay on the package cannot evaluate a symptom, identify a clot, or supply emergency care.
People sometimes ask whether switching from a soy food to a capsule settles an allergy question. Read the exact product’s allergen declaration. The Allergy Research Group panels identify soy. Nattovena’s panel includes its own allergen statement. A different statement on another brand is not evidence about your bottle, and someone with a serious soy allergy should verify the source and suitability with their clinician and the manufacturer before purchase.
Questions shoppers ask about FU and milligrams
Are 2,000 FU always equal to 100 mg?
No. That pairing is disclosed for the two NSK-SD servings compared here. It gives a ratio for those specified preparations. A different ingredient may disclose another activity per milligram or omit weight entirely. Use the activity claim from the particular product and ask for clarification if one of the quantities needed for your comparison is missing.
Does a 50 mg capsule have half the activity of the 100 mg softgel?
For these specific Allergy Research Group labels, the nominal per-capsule activity is half the amount declared for one 100 mg softgel. However, the 50 mg product defines a full serving as two capsules. Compare full servings and the activities match. This distinction is useful for recognizing a reorder and for checking how many servings are in the bottle.
Is a higher FU rating a better choice?
It is a higher labeled activity per unit when the serving and assay are comparable. It cannot decide who should take an enzyme, how often, or for what condition. If you are evaluating nattokinase because of a medical concern, share the three product panels with a clinician rather than using the graph as a ranking of outcomes.
Can I use a natto food serving as an equivalent?
A portion of fermented soybeans is a food with multiple components, and you may not have an activity test for that specific portion. The amount by weight does not let you assign it the same FU as a tested supplement. Enjoying natto as part of a meal and comparing enzyme supplement labels involve different decisions.
Why might a 180-count bottle last a different amount of time than expected?
First establish whether the count refers to capsules or softgels. Divide by the units per full serving, and only then look at the directions. A 180-softgel bottle with one softgel per serving contains 180 full servings. A hypothetical 180-capsule bottle with two capsules per serving would contain 90. How often a serving is used is a separate question.
Where can I see the exact formulas again?
Our Heart & Circulation collection includes all three products. The Nattovena product guide focuses on that single formula. For a comparison you can reuse, write down the full serving, FU, capsule count and exact product name. Those four details survive a change in packaging much better than a memory of which label looked strongest.