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NOW Foods vs Doctor's Best Phosphatidylserine (2026)
Disclosure: We earn commissions on purchases made through our links. This never influences our scores. Editorial policy
The Verdict
NOW Foods edges it on our rubric, 82 to 81 on our 0-100 execution score. Dosing and form ties at 22 and transparency ties at 23. NOW wins purity verification 19 to 16 on its testing program; Doctor's Best wins value 20 to 18 and holds our Best Value badge in the phosphatidylserine scorecard, on the reasoning in its own note that it is the cheapest verified branded-extract PS after the 2026 category repricing. On raw cost per 300mg day NOW is the cheaper of the two, about $0.55 against $0.72, with an unnamed source. In our view that is the trade in one sentence: pay about seventeen cents a day more for a named branded extract, or keep the money and rely on NOW's testing program instead of on the ingredient brand.
We would take the named extract if the goal is to match the material the trials used, and NOW otherwise. The framing our profile insists on either way is the honest ceiling on both products: the FDA allows a qualified health claim here for cognitive dysfunction in the elderly while flagging the evidence itself as limited and inconclusive.
Phosphatidyl Serine 100mg
NOW Foods
Phosphatidylserine 100mg with SerinAid
Doctor's Best
Head-to-Head Comparison
| Category | Phosphatidyl Serine 100mg NOW Foods | Phosphatidylserine 100mg with SerinAid Doctor's Best |
|---|---|---|
| Brand Score | 82/100Winner | 81/100 |
| Dosing & Form | 22/25Winner | 22/25 |
| Purity | 19/25Winner | 16/25 |
| Value | 18/25 | 20/25Winner |
| Transparency | 23/25Winner | 23/25 |
| Cost/Day | $0.55Winner | $0.72 |
| Dose/Serving | 100mg | 100mg |
| Form | Soy-Derived Vegetarian Capsule | SerinAid Soy-Derived Vegetarian Capsule |
| Third-Party Tested | ✓ Yes | No |
| Proprietary Blend | No | No |
Why This Comparison Matters
Both of these are 100mg soy-derived phosphatidylserine capsules, both take three capsules to reach the 300mg a day our profile lists for cognitive use, and they finish one point apart. The difference between them is whether the source extract is named.
Doctor's Best identifies SerinAid, the Chemi Nutra branded phosphatidylserine, on the label; our notes call it a legitimate alternate branded form and say the trials behind the soy-PS category used either Sharp-PS or SerinAid. NOW does not call out a branded extract on this SKU, so our notes describe the source as unidentified, but NOW operates NPA A-rated GMP facilities with in-house and third-party testing and publishes lot-level data. Neither carries USP or NSF certification and both are vegetarian capsules.
On cost, NOW is about $0.55 per 300mg day from $21.99 for 120 capsules, and Doctor's Best is about $0.72 from $28.99 for 120 capsules. Our profile notes that the cognitive trials use 100mg three times daily while the exercise cortisol trials use 600 to 800mg a day, which are very different dose tiers.
Detailed Score Breakdown
Phosphatidyl Serine 100mg
NOW Foods
Soy lecithin-derived phosphatidylserine; NOW does not call out a branded extract on this SKU, so the source is generic Sharp-PS-tier rather than identified
NOW operates NPA A-rated GMP facilities with in-house and third-party testing; published lot-level COAs
$0.55/day at 300mg (3 caps) - middle of the pack
Full disclosure, no proprietary blend, but the PS source extract is not branded on the label
NOW publicly tested and called out other PS brands for under-delivering on label-claimed PS content; their own SKU is consistent with label
Phosphatidylserine 100mg with SerinAid
Doctor's Best
Uses SerinAid (Chemi Nutra) soy-derived PS, an alternate branded form with its own clinical sourcing rather than Sharp-PS
Doctor's Best produces in GMP facilities and identifies the SerinAid branded extract on the label; no NSF/USP certification
$0.72/day at 300mg (3 caps, $28.99 for 120ct) - the cheapest verified branded-extract PS after the 2026 category repricing
SerinAid identified on label, full disclosure, vegan capsule shell
SerinAid is a legitimate alternate branded PS - the trials behind the soy-PS category have used either Sharp-PS or SerinAid
How We Compared These Products
Every product in our database is scored on four equally-weighted pillars: dosing accuracy and form quality, purity verification (third-party testing), cost per clinically effective dose (not cost per pill), and label transparency. Each pillar is worth 25 points for a total of 100.
Cost per effective dose is calculated using the clinically studied dose from published research, not the manufacturer's suggested serving. If a product requires multiple servings to reach the dose used in clinical trials, that cost is reflected in the value score.
For a full explanation of our scoring methodology, see our methodology page. Prices were last checked on the dates listed for each product and may have changed.
Frequently Asked Questions
What is SerinAid and does the branded extract matter?
SerinAid is the Chemi Nutra branded soy-derived phosphatidylserine used in the Doctor's Best product. Our notes call it a legitimate alternate branded form and say the trials behind the soy-PS category have used either Sharp-PS or SerinAid, so it is trial-relevant material. NOW does not name a branded extract on this SKU, which its own notes list as a con.
Which phosphatidylserine is cheaper per day?
NOW, at about $0.55 per 300mg day against Doctor's Best at about $0.72. Both bottles hold 120 capsules, at $21.99 and $28.99. Our Best Value badge still sits with Doctor's Best, on the reasoning in its own note that it is the cheapest verified branded-extract PS after the 2026 category repricing, and our value pillar splits 20 to 18 in its favor.
How many capsules a day do these take?
Three of either, since both are 100mg per capsule and our profile lists 100mg three times daily, 300mg total, for cognitive use. That gives 40 days from a 120-capsule bottle. Our profile notes the exercise cortisol trials run much higher at 600 to 800mg a day, which would double or nearly triple that capsule count.
More Phosphatidylserine Comparisons
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FDA Disclaimer: These statements have not been evaluated by the Food and Drug Administration. Dietary supplements are not intended to diagnose, treat, cure, or prevent any disease. Always consult with a qualified healthcare professional before starting any supplement regimen.