Potassium chloride vs citrate: cheap and dense vs gentle and alkalinizing

Potassium has the inverse problem of magnesium. Magnesium has many forms with very different absorption profiles; potassium has many forms with very similar absorption profiles. Once potassium dissociates from its counter-ion in the gut, it absorbs like any other potassium ion — there's no "slow potassium" or "fast potassium" the way there's slow and fast magnesium. The form question for potassium is mostly about three other things: how much elemental potassium per gram (density), what the counter-ion contributes (acid-base balance, taste), and what the U.S. 99mg pill convention does to your buying options.

Density matters most for electrolyte drinks. Potassium chloride is 52% potassium by weight; anhydrous potassium citrate is about 38%. To deliver 380mg of potassium (roughly the Liquid I.V. dose), you need 0.73g of KCl or about 1.0g of anhydrous citrate — a meaningful size difference. In a 16g electrolyte stick, this matters because powder volume is constrained by the sachet. Every clinical ORS, including the WHO formula, uses KCl for this reason. Re-Lyte, LMNT, Liquid I.V., and Nuun all use KCl as their primary potassium source. The DIY Lyte Lab builder defaults to KCl for the same reason — it's the cheapest, densest, and most clinically validated path.

The counter-ion matters most for clinical use cases. Potassium citrate is metabolized to potassium plus bicarbonate, making it alkalinizing — a small but real net base-load increase to the body. This is why nephrologists prescribe potassium citrate to patients with calcium-oxalate kidney stones (Curhan 1996; AUA guidelines): the citrate inhibits stone formation through urinary citrate elevation and the alkalinization is mildly protective. For someone without stone history, this advantage is irrelevant. For someone with a history, it's significant — and the form choice changes from cost-driven to clinical.

The 99mg potassium tablet convention is the most under-discussed piece of the potassium puzzle. FDA drug-labeling rules and historical small-bowel lesion concerns shaped the U.S. pill market, so many retail potassium pills are tiny (~99mg per pill). That is not a universal FDA cap on all potassium foods, diluted powders, or prescription potassium. Electrolyte drinks at 200-400mg per serving and KCl powder sold as salt substitute are regulated differently from solid oral potassium drug products. Potassium citrate prescription products at 5-15mEq per tablet (195-585mg potassium) are how serious dosing happens under medical supervision.

An honest framing: for daily diet, potassium from food (bananas, potatoes, leafy greens, legumes) is usually better than supplements because you get water, fiber, and the rest of the food matrix. For electrolyte drinks at 200-400mg/serving, KCl is the right pick. For prescription stone prevention or specific clinical protocols, citrate at higher doses under medical supervision is the right pick. For retail pills, both KCl and gluconate are commonly sold around 99mg, but you'd need 10-30 of them to hit a meaningful daily deficit, which makes them an inefficient supplementation tool.