Potassium supplements stop at 99 mg because two United States drug rules draw a line at 100 mg of potassium per tablet, not because the Food and Drug Administration limits how much potassium a supplement may contain. One, section 201.306 of title 21 of the Code of Federal Regulations, cited as 21 CFR 201.306, requires some potassium salt tablets supplying 100 mg or more to carry a warning about small-bowel injury. The other, 21 CFR 216.24, lists solid potassium chloride products at that level among drug products withdrawn from the market. Ninety-nine sits one milligram under the line, and the agency has never ruled on whether a supplement above it needs the warning. For how much potassium adults need in a day, see what the 3,400 mg daily potassium target looks like in food.
Written by Dr Brad Stanfield, a general practitioner registered in New Zealand and Australia. Check every number against the sources at the end. This is general information, not medical advice.
The short version
- 21 CFR 201.306 is a drug labeling rule. It sits in Title 21, Subchapter C, which covers drugs, and it reaches coated tablets of a potassium salt supplying 100 milligrams or more of potassium each, uncoated tablets at the same level, and liquid preparations at 20 milligrams or more of potassium per milliliter.
- A second drug rule, 21 CFR 216.24, lists solid potassium chloride products supplying 100 mg or more of potassium per dose among drug products withdrawn from the market for reasons of safety or effectiveness. Controlled-release forms and products meant to be dissolved before drinking are left out. The approvals were withdrawn in 1977 and 1992.
- On their text both rules are written for drugs, and the Food and Drug Administration has never ruled on whether they apply to supplements. Section 411 of the Federal Food, Drug, and Cosmetic Act, added in 1976, bars the Secretary of Health and Human Services from setting maximum potency limits on a vitamin or mineral under the misbranding and food-standard provisions.
- The National Institutes of Health Office of Dietary Supplements states that the Food and Drug Administration "has not issued a ruling about whether dietary supplements containing more than 99 mg potassium must carry a warning label".
- Supplements above 99 mg are already on sale. The same label database that records NOW potassium citrate capsules at 99 mg records NOW potassium citrate powder at 448 mg per quarter teaspoon.
- 99 mg is 2 percent of the 4,700 mg Daily Value for potassium. One medium banana carries 422 mg, and the 2019 Adequate Intake is 3,400 mg a day for men and 2,600 mg for women.
What 21 CFR 201.306 actually says
21 CFR 201.306 is titled "Potassium salt preparations intended for oral ingestion by man". It sits in Title 21, Subchapter C, which is headed "Drugs: General", inside Part 201 on labeling and Subpart G on specific labeling requirements for specific drug products. Everything in it is addressed to a drug. The Code of Federal Regulations dates the current text to the Federal Register of 27 March 1975, at volume 40, page 13998, which lawyers write as 40 FR 13998.
Paragraph (a) says the Food and Drug Administration "will initiate no regulatory action with respect to the continued marketing of coated tablets containing potassium chloride or other potassium salts which supply 100 milligrams or more of potassium per tablet" provided several conditions are met. The label has to carry the prescription caution statement from section 503(b)(4) of the Act. The labeling has to carry a warning about small-bowel injury, reproduced word for word inside the regulation. Any other labeling or advertising has to match it, and the manufacturer has to file a new drug application.
Paragraph (b) handles the uncoated version. The agency may act against uncoated tablets supplying 100 milligrams or more of potassium each, and against liquid preparations supplying 20 milligrams or more of potassium per milliliter, unless those products are prescription-only and their labeling tells the prescriber to have patients dissolve the tablet or dilute the liquid before swallowing it.
Read the two paragraphs together and the threshold is 100 milligrams of potassium in one dose unit. Ninety-nine is the largest whole number underneath it. The National Institutes of Health Office of Dietary Supplements gives two reasons manufacturers hold potassium at 99 mg: this labeling rule, and the Food and Drug Administration's finding, covered below under 21 CFR 216.24, that some potassium chloride drug products above 99 mg are not safe. Both are drug rules, and the category was built around them rather than around a dose.
What 21 CFR 201.72, the over-the-counter potassium rule, requires
21 CFR 201.72 is the other potassium rule inside Part 201. It sits in Subpart C, the subpart that governs over-the-counter drug labeling rather than prescription products. It requires an over-the-counter oral product to declare its potassium content when a single maximum recommended dose supplies 5 milligrams or more. It requires the warning "Ask a doctor before use if you have kidney disease, a potassium-restricted diet" when the labeled maximum daily dose carries more than 975 milligrams of potassium. Published in 2004 at 69 FR 13734, it draws its line at 975 mg a day, about ten times what a 99 mg pill delivers, and it produces no 99 mg figure anywhere.
Who 21 CFR 201.306 is written for
A dietary supplement is treated as a food in the United States. Section 201(ff) of the Federal Food, Drug, and Cosmetic Act deems it to be one, and a product sold for diagnosing, treating, curing or preventing a disease is regulated as a drug. 21 CFR 201.306 speaks throughout about prescription status, practitioners and new drug applications, none of which exist in the supplement framework. On its text the rule is written for drugs, and the Food and Drug Administration has never ruled on whether it applies to a supplement.
Where the small-bowel warning in 21 CFR 201.306 came from
The warning that 21 CFR 201.306 requires is printed inside the regulation, and it describes a specific problem from the 1960s. It opens: "There have been several reports, published and unpublished, concerning nonspecific small-bowel lesions consisting of stenosis, with or without ulceration, associated with the administration of enteric-coated thiazides with potassium salts." It goes on to say those lesions caused obstruction, hemorrhage and perforation, that surgery was frequently required, and that deaths occurred.
The reports behind that paragraph are real and they are dated. The Journal of the American Medical Association, JAMA, published the first on 16 November 1964: Baker, Schrader and Hitchcock, "Small-bowel ulceration apparently associated with thiazide and potassium therapy". Its issue of 22 February 1965 carried two more papers, one a clinical series titled "The circumferential small-bowel ulcer: clinical aspects in 17 patients" and one titled "Ulcerative-obstructive lesions of the small intestine". On 31 May 1965 Boley and colleagues published an experimental study asking whether thiazides and potassium could produce the lesions deliberately.
The regulation is more careful than the folklore it produced. Its own warning text says: "Based on a large survey of physicians and hospitals, both United States and foreign, the incidence of these lesions is low, and a causal relationship in man has not been definitely established." It also states the scope of the concern: the warning applies to "any capsule or coated tablet of a potassium salt intended for oral ingestion without prior dilution with an adequate volume of liquid to preclude gastrointestinal injury". The worry was a concentrated solid resting against the wall of the small intestine, not potassium as a nutrient.
What 21 CFR 216.24 says about potassium chloride
21 CFR 216.24 is the Food and Drug Administration list of drug products "withdrawn or removed from the market because such drug products or components of such drug products have been found to be unsafe or not effective". Products on that list may not be compounded under the exemptions in the Act. One entry reads: "Potassium chloride: All solid oral dosage form drug products containing potassium chloride that supply 100 milligrams or more of potassium per dosage unit (except for controlled-release dosage forms and those products formulated for preparation of solution prior to ingestion)."
The proposed rule that introduced the list, published in the Federal Register on 8 October 1998 at volume 63, page 54082, gives the agency's reason in a single sentence: "Concentrated solid oral dosage forms of potassium salt were associated with small bowel lesions." The same page records that approvals for those drug products were withdrawn on 29 July 1977 and on 29 April 1992. The final rule was published on 8 March 1999 at 64 FR 10944 and took effect on 7 April 1999.
The entry carves out two things. Controlled-release forms are excluded, and so is anything "formulated for preparation of solution prior to ingestion", which means a powder dissolved in water before it is drunk. The agency was regulating how a concentrated solid behaves in the gut, which is why the form of the dose changes the answer even on the drug side of the line.
Why the Food and Drug Administration does not cap potassium in a supplement
Section 411 of the Federal Food, Drug, and Cosmetic Act, codified at 21 U.S.C. 350, is the reason. Congress added it through the Vitamin-Mineral Amendments of 1976, Public Law 94-278. The Secretary "may not establish, under section 321(n), 341, or 343 of this title, maximum limits on the potency of any synthetic or natural vitamin or mineral within a food to which this section applies". The next clause adds that the Secretary "may not classify any natural or synthetic vitamin or mineral (or combination thereof) as a drug solely because it exceeds the level of potency which the Secretary determines is nutritionally rational or useful".
That protection has a boundary. Section 411(a)(2) switches it off where a product is "represented for use by individuals in the treatment or management of specific diseases or disorders, by children, or by pregnant or lactating women". Sell a mineral for a disease and the shield goes away.
The Dietary Supplement Health and Education Act of 1994, Public Law 103-417, amended section 411 to add powders, softgels and gelcaps to the forms it covers, and it wrote the safety standard that stands in place of a potency limit. Under section 402(f), 21 U.S.C. 342(f), a supplement is adulterated if it "presents a significant or unreasonable risk of illness or injury" under the conditions of use its labeling recommends. The same paragraph adds: "In any proceeding under this subparagraph, the United States shall bear the burden of proof on each element to show that a dietary supplement is adulterated."
Under that paragraph the agency can act against a potassium supplement, and carries the burden of proving the risk. The National Institutes of Health Office of Dietary Supplements records the position in its potassium fact sheet, updated 2 June 2022: the Food and Drug Administration "has not issued a ruling about whether dietary supplements containing more than 99 mg potassium must carry a warning label". The Council for Responsible Nutrition, the supplement industry's own trade association, answered a member asking the same question in 2019. Its reply says the 99 mg figure "is specific to OTC drugs", meaning over-the-counter medicines, that the agency "has not actually ruled or commented on potassium in dietary supplements", and that "FDA does not set maximums for supplements". It ends with this advice: "But due to the nature of the safety concern, which presumably would apply to supplements and OTC drugs equally, it would be prudent for manufacturers to stick with the less than 100 mg limit or consider the warning statement for liability reasons."
No one in that exchange points to a rule that caps potassium in a supplement. The trade association still advises its own members to stay under 100 mg or carry the warning, because it presumes the safety concern behind the drug rules applies to supplements too.
What potassium supplements actually contain
The National Institutes of Health Dietary Supplement Label Database holds the Supplement Facts panels from tens of thousands of products, which makes the convention checkable rather than assumed. Potassium-only pills mostly sit at or just below the threshold. The formats that are not pills ignore it.
| Product, as the label reads | Serving | Potassium (% of Daily Value) |
|---|---|---|
| Nature Made Potassium Gluconate 550 mg | 1 tablet | 90 mg (1.9%) |
| NOW Potassium Citrate 99 mg | 1 veg capsule | 99 mg (2.1%) |
| Solaray Potassium Citrate 99 mg | 1 vegcap | 99 mg (2.1%) |
| Pure Encapsulations Potassium (Citrate) | 1 capsule | 200 mg (4.3%) |
| Nutricost Potassium Chloride 365 mg | 0.7 g powder | 365 mg (7.8%) |
| Liquid I.V. Hydration Multiplier | 16 g stick | 370 mg (7.9%) |
| NOW Potassium Citrate powder | 0.25 level teaspoon | 448 mg (9.5%) |
| Dr. Clark Research Potassium Citrate 530 mg | 4 capsules | 760 mg (16.2%) |
All eight panels come from the Dietary Supplement Label Database. The percentages are calculated here against the current 4,700 mg Daily Value in 21 CFR 101.9 rather than copied from the labels, because some of the older panels were entered before that Daily Value took effect. Two of these products carry more than 99 mg in a capsule, which is the format the drug rule was written about, and they are sold openly.
The sharpest test is a single brand. NOW sells potassium citrate as a 99 mg veg capsule and as a powder, and the powder declares 448 mg in a quarter of a level teaspoon. Same company, same potassium salt, and 4.5 times the dose decided by the container.
Why the front of the bottle and the Supplement Facts panel disagree
The number printed on the front of the bottle is usually the weight of the whole salt, while the Supplement Facts panel gives elemental potassium, which trips people up more often than the regulation does. A Nature Made tablet prints 550 mg of potassium gluconate on the front and declares 90 mg of potassium in the Supplement Facts panel. Potassium is 16.7 percent of potassium gluconate by weight, so the compound weight on the front runs about six times the mineral weight on the back. The same arithmetic for each common salt, from chloride at 52.4 percent potassium to gluconate at 16.7, is worked through in how much potassium each potassium salt carries.
How 99 mg compares with a day of potassium
In 2019 the National Academies of Sciences, Engineering, and Medicine published Dietary Reference Intakes for Sodium and Potassium and set the adult Adequate Intake at 3,400 mg a day for men aged 19 and over and 2,600 mg for women. The committee found the data insufficient to derive an Estimated Average Requirement, which is why the number is an Adequate Intake rather than a Recommended Dietary Allowance. It also declined to set a Tolerable Upper Intake Level for potassium, and declined to set a chronic disease risk reduction intake, in both cases for want of evidence.
Against those numbers a 99 mg pill is a small fraction of a day. It is 2.9 percent of the male Adequate Intake, 3.8 percent of the female one, and 2.1 percent of the 4,700 mg Daily Value printed on United States labels. One medium banana carries 422 mg, more than four such pills. The Office of Dietary Supplements records the practical consequence from the 2013 to 2014 National Health and Nutrition Examination Survey: among the 12 percent of Americans aged 2 and over who take a potassium-containing supplement, it adds a mean of 87 mg to the day.
Who should not take supplemental potassium
Supplemental potassium is genuinely hazardous for some people, and the list is short enough to read in full. Do not take a potassium supplement, a potassium salt substitute or an electrolyte powder carrying potassium without asking your own doctor first if you have chronic kidney disease or any condition that impairs potassium excretion, if you have been told to limit potassium, or if you take an angiotensin converting enzyme inhibitor such as benazepril, an angiotensin receptor blocker such as losartan, or a potassium-sparing diuretic such as spironolactone or amiloride. The Office of Dietary Supplements notes that in people with impaired urinary potassium excretion, "even dietary potassium intakes below the AI can cause hyperkalemia", where AI is the Adequate Intake, and advises anyone at risk to ask a doctor or registered dietitian about potassium from all sources: food, supplements and salt substitutes together. Hyperkalemia is potassium high enough in the blood to be dangerous, and severe cases can cause muscle weakness, paralysis, palpitations and heart rhythms that are life threatening. Milder cases often cause no symptoms at all.
Two other cautions belong on the same list. Do not stack sources without counting them, because a supplement, a salt substitute and an electrolyte sachet taken on the same day add together. Type 1 diabetes, congestive heart failure, adrenal insufficiency and liver disease also raise the risk, so the same conversation applies. If you are in any of these groups, the fact that a supplement is on sale is not the question you should be asking.
Why this drink carries 500 mg when potassium pills stop at 99
This article is published on a store that sells a potassium drink, so the obvious question deserves a direct answer. Potassium Fiber is a drink powder with 500 mg of potassium as potassium citrate and 8 grams of fiber from acacia gum per serving, five times the 99 mg convention; the case for acacia gum over the other fiber supplements is made separately. On their text both rules are written for drugs, and the Food and Drug Administration has never ruled on whether they apply to supplements. Both targeted concentrated doses swallowed without dilution; this drink is stirred into at least 300 mL of water before it is drunk.
The 500 mg was chosen as a share of the day rather than against either rule. It is about 15 to 19 percent of the adult Adequate Intake of 3,400 mg for men and 2,600 mg for women, a top-up rather than a large single dose, and larger single doses of potassium are harder to hide in a drink.
None of that makes extra potassium right for everyone. The list above of people who should not take supplemental potassium without their doctor's advice applies to this drink as much as to any pill.
What the 99 mg rules do not settle
This article makes no claim that a larger dose of potassium is better for you than a smaller one, and no claim about what supplemental potassium does to any health outcome. It answers a regulatory question only: where the 99 mg figure came from and what it binds. The absence of a Tolerable Upper Intake Level is not permission, and the National Academies committee was explicit that it withheld one for lack of evidence rather than as a finding of safety at any dose. The reason to write it down is that the question is usually answered with a flat claim that the Food and Drug Administration caps supplements at 99 mg. The statutes and the three regulations quoted above say something narrower, and the difference is what you need if you are trying to read a label.
Sources
- United States Food and Drug Administration. Potassium salt preparations intended for oral ingestion by man. 21 CFR 201.306 [40 FR 13998, 27 March 1975, as amended at 55 FR 11576 and 67 FR 4906]. govinfo.gov
- United States Food and Drug Administration. Potassium labeling. 21 CFR 201.72 [69 FR 13734, 24 March 2004]. The over-the-counter drug labeling rule, requiring a warning above 975 mg of potassium in the labeled maximum daily dose. govinfo.gov
- United States Food and Drug Administration. Drug products withdrawn or removed from the market for reasons of safety or effectiveness. 21 CFR 216.24 [81 FR 69676, 7 October 2016, as amended at 83 FR 63573]. govinfo.gov
- United States Food and Drug Administration. List of Drug Products That Have Been Withdrawn or Removed From the Market for Reasons of Safety or Effectiveness. Proposed rule. Federal Register. 1998;63:54082 (potassium chloride entry at 54086). govinfo.gov
- United States Food and Drug Administration. List of Drug Products That Have Been Withdrawn or Removed From the Market for Reasons of Safety or Effectiveness. Final rule. Federal Register. 1999;64:10944. govinfo.gov
- Vitamins and minerals. 21 U.S.C. 350 (section 411 of the Federal Food, Drug, and Cosmetic Act), added by Public Law 94-278, 22 April 1976, amended by Public Law 103-417, 25 October 1994. govinfo.gov
- Adulterated food. 21 U.S.C. 342(f) (section 402(f) of the Federal Food, Drug, and Cosmetic Act), added by the Dietary Supplement Health and Education Act of 1994, Public Law 103-417. govinfo.gov
- Baker DR, Schrader WH, Hitchcock CR. Small-bowel ulceration apparently associated with thiazide and potassium therapy. JAMA. 1964;190:586-590. doi:10.1001/jama.1964.03070200022005. PubMed 14215519
- Morgenstern L, Freilich M, Panish JF. The circumferential small-bowel ulcer: clinical aspects in 17 patients. JAMA. 1965;191:637-640. doi:10.1001/jama.1965.03080080027006. PubMed 14242420
- Lawrason FD, Alpert E, Mohr FL, McMahon FG. Ulcerative-obstructive lesions of the small intestine. JAMA. 1965;191:641-644. doi:10.1001/jama.1965.03080080031007. PubMed 14242421
- Boley SJ, Schultz L, Krieger H, Schwartz S, Elguezabal A, Allen AC. Experimental evaluation of thiazides and potassium as a cause of small-bowel ulcer. JAMA. 1965;192:763-768. doi:10.1001/jama.1965.03080220027006. PubMed 14285709
- National Institutes of Health, Office of Dietary Supplements. Potassium: Fact Sheet for Health Professionals. Updated 2 June 2022. ods.od.nih.gov
- National Institutes of Health. Dietary Supplement Label Database. Label records 9198, 313976, 338535, 278239, 270725, 249696, 313975 and 223474. dsld.od.nih.gov
- National Academies of Sciences, Engineering, and Medicine. Dietary Reference Intakes for Sodium and Potassium. Washington DC: The National Academies Press; 2019. doi:10.17226/25353. doi.org
- United States Food and Drug Administration. Nutrition labeling of food: reference daily values. 21 CFR 101.9(c)(8)(iv). Potassium, 4,700 mg. govinfo.gov
- Council for Responsible Nutrition. Does FDA have an Upper Limit for potassium? CRN Experts: Here for you with answers to your regulatory questions. 29 April 2019. crnusa.org
This article is general information, not medical advice. Nothing here is legal advice either. Potassium Fiber is a drink powder containing 500 mg of potassium as potassium citrate and 8 grams of fiber from acacia gum per serving, on pre-sale and shipping from 1 December 2026.