A high blood potassium concentration — hyperkalemia[1] — is associated with an increased risk of heart problems (e.g., heart arrhythmias).[2][3][4][5] Hyperkalemia-related symptoms have been associated with salt substitutes in several case studies,[6][7][8][9][10] but case studies of individual people only show what is possible rather than what is typical.
In people without known health conditions, serum potassium concentrations are between 3.5 and 4.5 millimoles per liter of blood (mmol/L).[11][12][13] A meta-analysis of randomized controlled trials found that daily supplementation with potassium chloride in the range of 22 to 140 mmol/day — equivalent to approximately 0.9 to 5.5 grams/day of potassium — caused a statistically significant but clinically meaningless increase (+0.14 mmol/L) in serum potassium.[14] Therefore, generally, supplementation with potassium is unlikely to cause hyperkalemia. Furthermore, in potassium supplementation studies, adverse effects are uncommon and biomarkers of renal function (urinary and serum sodium and creatinine) are typically unaffected.[14]
While supplementation with potassium salts (e.g. potassium chloride) can improve (i.e., lower) blood pressure,[15][16][17][18][19] some evidence shows that very high doses might increase blood pressure.[20] Consequently, if you use a potassium salt to treat high blood pressure, always use the dose recommended by your doctor.