Fact check: Tiny amounts of potassium in vaccine doses are not harmful

A popular Facebook post, described as being written by an anonymous doctor, falsely claims that Potassium Chloride, which is an ingredient in some vaccines, is dangerous in any amount and that it will kill recipients or causes miscarriages. Potassium Chloride in small amounts is safe and is given intravenously to treat potassium depletion. Monitoring of people who received vaccines for COVID-19 indicates that the vaccines are safe.

Reuters Fact Check. REUTERS

The post says: “A direct injection of ANY AMOUNT of Potassium Chloride (KCl) into the blood will in fact cause heart irregularities (palpitations and tachycardia) in even the most healthy of people (because it causes disruptions in the sodium-potassium pump mechanism essential for healthy heart function) - but in the elderly - even miniscule amounts directly injected into the blood will often cause death.  Any amount of KCl directly injected into the blood of a pregnant woman will also likely cause a miscarriage.” (here).

Potassium levels vary within a range in human blood, and can cause serious medical problems when they rise or fall out of this range (here). 

Potassium chloride, also called potassium salt or KCl, is a salt that is regularly used orally to raise potassium levels in the blood of people who are potassium deficient and is given intravenously in severe cases (see p. 490 here here).

In a case where enough potassium chloride was given that it raises blood potassium levels above the safe range, this could cause death from cardiac depression, arrhythmias or heart attacks (here).

The Moderna COVID-19 vaccine doesn’t use any potassium chloride (here).

The Pfizer COVID-19 vaccine lists potassium chloride in its ingredients, along with potassium dihydrogen phosphate, but these substances are present in very small doses. “This vaccine contains potassium, less than 1 mmol (39 mg) per dose, i.e. essentially ‘potassium-free',” a patient information leaflet says (pdf here).

For comparison, the amount of potassium in the blood ranges from 3.6 to 5.2 millimoles (mmol) per litre (here). Adults have around 5-6 litres of blood in their body.

Reports that could indicate problems with the COVID-19 vaccines are closely monitored, but data after hundreds of millions of doses tally with trials that showed the vaccines are safe. Reuters has written about how the number of deaths (here) and severe adverse effects (here) reported in people who have received the vaccine do not differ significantly from what would be expected if they had not.


False. While very high levels of potassium in the bloodstream can cause medical problems, there is only a tiny amount of potassium in the Pfizer COVID-19 vaccine and none in the Moderna vaccine. Potassium chloride can be given intravenously and in highly controlled amounts is a treatment for severe potassium deficiency. Data from trials and COVID-19 vaccine rollouts show that the vaccines are safe.

Read more about our work to fact-check social media posts here .