Label arithmetic · NIH DSLD 295971
Source Naturals Magnesium Citrate 133 mg: 133 mg of magnesium per capsule, 1–3 capsules a day
133 mg of magnesium per capsule; the label's 1–3 capsules a day give 133–399 mg. No US price matched (Nov 2). Inside: salt weight, capsule size.
Source Naturals Magnesium Citrate 133 mg declares 133 mg of elemental magnesium per serving as citrate, which needs 823–1,177 mg of magnesium citrate in each capsule, against 1,100 mg in the largest standard capsule (size 000) at powder density 0.8 g/mL, the top of the usual 0.6–0.8 range: it fits only that size. No US retail price matched as of 2026-11-02; 17 of the 135 citrate labels in this registry have a matched price. NIH DSLD 295971, label dated 2023-08-23.
computed from the filed label
Chart data
| Displayed chart text |
|---|
| 545 mg |
| 730 mg |
| 1,100 mg |
| 823–1,177 mg of citrate per capsule |
Data release 2026-08-10-f441aa9f · registry snapshot 2026-08-10 · latest price observation 2026-10-19 · chemistry 2026-10-17
Mass: 823–1,177 mg per capsule · Price: none matched · % DV: 33% vs 32%
Elemental: The magnesium itself; the rest of the compound weight is the partner molecule.
Compound: The whole salt, such as magnesium glycinate, that must physically fit in the capsule.
Size 000: The largest standard capsule, about 1,100 mg of powder at 0.8 g/mL, the top of the usual 0.6–0.8 range; size 00 holds about 730 mg and size 0 about 545 mg.
Recompute with your price
Enter the price you paid; the declared amount and servings of this label are prefilled, so the result is the cost per 100 mg of elemental magnesium for your bottle.
Same-salt comparison appears here.
Will 133 mg of citrate actually fit in one capsule, or do I need more than one?
Estimated salt mass versus assumed capsule capacity: Source Naturals Magnesium Citrate 133 mg implies 823–1,177 mg of magnesium citrate in each capsule to deliver 133 mg of elemental magnesium, against 1,100 mg in the largest standard capsule (size 000) at powder density 0.8 g/mL, the top of the usual 0.6–0.8 range. Verdict: needs size 000, read at the most favourable hydration and the most units per serving.
computed with assumption| Measure | Value |
|---|---|
| Elemental magnesium per serving | 133 mg |
| Units per serving | 1 |
| Magnesium citrate per serving | 823–1,177 mg |
| Magnesium citrate per capsule | 823–1,177 mg |
| Capsule capacity 0 · 00 · 000 | 545 · 730 · 1,100 mg |
| Verdict | Needs size 000 |
The filed salt can have more than one hydration state (trimagnesium dicitrate 16.2%; dibasic and hydrated forms as low as 11.3%), so the compound mass is a range.
Source · NIH DSLD 295971 · label 2023-08-23; snapshot 2026-08-10 · release 2026-08-10-f441aa9f · CSV · method
How much elemental magnesium is actually in this label's filed magnesium lines?
Source Naturals Magnesium Citrate 133 mg files 1 magnesium line in NIH DSLD 295971; the selected primary line declares 133 mg of elemental magnesium per serving, against 0 other rows excluded from the primary amount. A salt named under another nutrient does not turn that nutrient's quantity into elemental magnesium.
measured| Filed amount | Salt or note as filed | Role |
|---|---|---|
| 133 mg | citrate · Magnesium (Form: as Magnesium Citrate) | Primary serving |
Source · NIH DSLD 295971 · label 2023-08-23; snapshot 2026-08-10 · release 2026-08-10-f441aa9f · CSV · method
Does this label's citrate claim hold up, or could the magnesium come from another source?
The label names one magnesium form, citrate, resolved from the filed magnesium line; at that salt the declaration is within the assumed size 000 capacity at powder density 0.8 g/mL, compared with oxide, the salt richest in magnesium at 60.3%.
computed with assumption| Form named on the label | Elemental fraction | Source |
|---|---|---|
| Magnesium citrate | 11.3–16.2% | filed magnesium line |
Source · NIH DSLD 295971 · label 2023-08-23; snapshot 2026-08-10 · release 2026-08-10-f441aa9f · CSV · method
Is this a good price for the elemental magnesium I'm actually getting?
No US retail price is matched to this label as of 2026-11-02; 17 of 135 citrate labels have one, against a median of $0.1159 per 100 mg among 12 ranked citrate offers.
computed
Chart data
| Displayed chart text |
|---|
| n=12 |
| P25 $0.0843 |
| P75 $0.1469 |
| median $0.1159 |
| Rank | Label | Per 100 mg | Observed |
|---|---|---|---|
| 1 | Best Naturals Magnesium Citrate 200 mg | $0.0344 | 2026-11-02 |
| 2 | Solgar Magnesium Citrate | $0.0607 | 2026-11-02 |
| 3 | LES Labs Magnesium Citrate | $0.0777 | 2026-11-02 |
| 4 | Bluebonnet Magnesium Citrate | $0.0865 | 2026-11-02 |
| 5 | Solaray Magnesium Citrate 400 mg | $0.0868 | 2026-11-02 |
| Median | 12 ranked citrate offers | $0.1159 | 2026-11-02 |
Source · Amazon via licensed data provider; NIH DSLD · unique ASIN × date; prices observed 2026-10-26 to 2026-11-02 · release 2026-08-10-f441aa9f · CSV · method
How many days will this bottle last at the label's own serving, and what does a day cost?
At the label's own serving, Source Naturals Magnesium Citrate 133 mg lasts 30–90 days: 90 servings against 1–3 servings a day in the filed directions.
computed| Measure | Value |
|---|---|
| Net contents as filed | 90 Capsule(s) |
| Serving size as filed | 1 Capsule(s) |
| Servings per container | 90 |
| Servings per day in the directions | 1–3 |
| Days per bottle | 30–90 days |
| $ per 30 days at one label serving a day | No ranked price as of 2026-11-02 |
| $ per 30 days at 420 mg Daily Value | No ranked price as of 2026-11-02 |
Source · NIH DSLD 295971 · label 2023-08-23; snapshot 2026-08-10 · release 2026-08-10-f441aa9f · CSV · method
What does "33% Daily Value" mean here, and does it recompute?
The label declares 33% Daily Value; 133 mg against the 420 mg reference in 21 CFR 101.9 recomputes to 32%, the same within one point.
computed| Group as filed | Declared | Reference | Recomputed |
|---|---|---|---|
| Adults and children 4 or more years of age | 33% | 420 mg | 32% |
Source · NIH DSLD 295971; 21 CFR 101.9 · label 2023-08-23 · release 2026-08-10-f441aa9f · CSV · method
Why does this label contain magnesium stearate, what shell is it, and who is it filed for?
Source Naturals Magnesium Citrate 133 mg files 4 other ingredients, including magnesium stearate (reference fraction 4.1% magnesium; no quantity filed, so it is not added to the total) and a gelatin shell, against 43 of 135 citrate labels that list magnesium stearate.
measured| Entry | Filed ingredient or declaration |
|---|---|
| 1 | Gelatin |
| 2 | Dibasic Calcium Phosphate |
| 3 | Silica |
| 4 | Magnesium Stearate |
| Shell | gelatin |
| Target group | Adult (18 - 50 Years) |
| Target group | Gluten Free |
| Target group | Dairy Free |
1 additional rows
| Entry | Filed ingredient or declaration |
|---|---|
| Target group | Sugar Free |
Source · NIH DSLD 295971 · label 2023-08-23; snapshot 2026-08-10 · release 2026-08-10-f441aa9f · CSV · method
What has research measured about citrate, and about side effects?
10 studies in the PubMed-checked registry measured outcomes involving citrate; 1 mention gastrointestinal or adverse outcomes. They measured the salt, not this label.
measured| Year | Study | PubMed |
|---|---|---|
| 2025 | Comparing the Bioavailability of Two Seawater-Derived Magnesium Preparations. | 40955524 |
| 2024 | Comparative Clinical Study on Magnesium Absorption and Side Effects After Oral Intake of Microencapsulated Magnesium (MAGSHAPE™ Microcapsules) Versus Other Magnesium Sources. | 39770988 |
| 2022 | Effects of short-term magnesium supplementation on ionized, total magnesium and other relevant electrolytes levels. | 35041150 |
Source · PubMed-checked study registry · registry checked 2026-08-10 · release 2026-08-10-f441aa9f · CSV · method
Has this brand had FDA recalls or adverse event reports?
Source Naturals has 6 FDA recall records matched by brand name in the enforcement data queried 2026-10-19. Source Naturals has FDA CAERS adverse event reports on record at brand level, as do 143 of 273 brands in this registry; openFDA states that “there is no certainty that the reported event (adverse event) was actually due to the product” and that reports “cannot be used to estimate the incidence of these events.”
measured| Recall | Date | Reason | Status |
|---|---|---|---|
| F-0100-2014 | 2013-11-13 | The firm found small piece of metal fragment in one tablet during its inspection process. | Terminated |
| F-1100-2014 | 2013-12-25 | Dietary Supplements were made with bulk products provided by National Enzyme Company which are currently under recall for chloramphenicol | Terminated |
| F-2178-2017 | 2017-05-10 | Testing of Vitamin D-3 as a result of a consumer complaint found specific lots to have lower concentrations than product specifications of ingredient labeling. | Terminated |
| F-2380-2017 | 2017-07-19 | Dietary supplements contain low levels of undeclared boron | Terminated |
| F-2383-2017 | 2017-07-19 | Dietary supplements contain low levels of undeclared boron | Terminated |
Source · openFDA enforcement and CAERS · queried 2026-10-19 · release 2026-08-10-f441aa9f · CSV · method
Is this the same formula as another brand's, and how do their prices differ?
Same filed formulation as 1 other labels of this brand; no other brand files it as of 2026-11-02.
computed| Label | Brand | Price per 100 mg |
|---|---|---|
| No cross-brand match as of 2026-11-02 |
Source · NIH DSLD 295971 · label 2023-08-23; snapshot 2026-08-10 · release 2026-08-10-f441aa9f · CSV · method
Which labels are closest to this one, with the same salt and dose?
6 labels use the same resolved citrate within ±10% of this label's 133 mg per unit, compared side by side on price and capsule verdict.
computed| Label | Elemental per unit | Price | Verdict |
|---|---|---|---|
| Source Naturals Magnesium Citrate 133 mg (DSLD 2954) | 133 mg | No price | Needs size 000 |
| Source Naturals Magnesium Citrate 133 mg (DSLD 295972) | 133 mg | No price | Needs size 000 |
| AN Amazing Nutrition Amazing Formulas Magnesium Citrate 400 mg | 133 mg | No price | Capsule sizes do not apply |
| Protocol For Life Balance Magnesium Citrate | 133 mg | No price | Capsule sizes do not apply |
| OL Olympian Labs Magnesium Citrate 400 mg (DSLD 326662) | 133 mg | No price | Needs size 000 |
| OL Olympian Labs Magnesium Citrate 400 mg (DSLD 326663) | 133 mg | No price | Needs size 000 |
Source · NIH DSLD 295971 · label 2023-08-23; snapshot 2026-08-10 · release 2026-08-10-f441aa9f · CSV · method
Where does this record come from, what is missing, and how do I cite or correct it?
Every value on this page traces to NIH DSLD 295971 (label 2023-08-23, snapshot 2026-08-10) and the chemistry model of 2026-09-13. 1 gap remain: No US retail price matched as of 2026-11-02 (barcode 0 21078 02099 8). The CSV carries the values shown here.
measured| Field | As filed |
|---|---|
| NIH DSLD label | NIH DSLD 295971 |
| Scanned label (PDF) | Label 295971 scan |
| Label date | 2023-08-23 |
| Date entered into DSLD | 2023-08-23 |
| Barcode (UPC) as filed | 0 21078 02099 8 |
| Label version · Package size difference, same product | NIH DSLD 274898 |
| Label version · Package size difference, same product | NIH DSLD 2954 |
| Label version · Package size difference, same product | NIH DSLD 295972 |
18 additional rows
| Field | As filed |
|---|---|
| Manufactured for | Source Naturals, Inc., Santa Cruz, CA |
| Claim category as filed | Nutrient |
| Claim category as filed | All Other |
| Claim category as filed | Structure/Function |
| FDA Statement of Identity | Dietary Supplement |
| Formulation re: Other | Supports bone and heart health |
| Suggested/Recommended/Usage/Directions | Suggested Use: 1 capsule 1 to 3 times daily with meals. |
| Precautions re: Pregnant or Nursing or Prescription Medications | Warning: If you are pregnant, may become pregnant, breastfeeding, have a history of kidney dysfunction or if you are taking any prescription drug, consult your health care professional before using this product. |
| Precautions re: All Other | If you experience loose stools, reduce your dosage. If symptoms persist, discontinue use and consult your health care professional immediately. |
| Storage | Store in a cool, dry place. |
| Formula re: Contains | Stress may interfere with the body's ability to absorb magnesium, so make sure your body has the optimal quantities. Magnesium Citrate is a highly absorbable form of magnesium, a profoundly important mineral that supports the body's bones, energy production, and glucose balance. Optimal intake of magnesium is essential to support relaxation and calming. Further, magnesium supports proper muscle function and is essential for cardiovascular health; in fact it is involved in over 300 cellular processes. |
| Formulation re: Does NOT Contain | Contains no yeast, dairy, egg, gluten, soy or wheat. Contains no sugar, starch, preservatives, or artificial color, flavor or fragrance. |
| Precautions re: All Other | Do not use if either tamper-evident seal is broken or missing. |
| Precautions re: Children | Keep out of the reach of children. |
| FDA Disclaimer Statement | These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease. |
| Brand IP Statement(s) re: (c), (TM), (SM) | Copyright SOURCE NATURALS, INC. |
| Physical state | Capsule |
| Registry snapshot | 2026-08-10 |
Source · NIH DSLD 295971 · label 2023-08-23; snapshot 2026-08-10 · release 2026-08-10-f441aa9f · CSV · method
6 brand pages linked below contain magnesium labels from the NIH DSLD registry snapshot dated 2026-08-10.