text: An example demonstrating how drug combination with additive effect can cause adverse effects is the co-administration of ACEI and potassium-sparing diuretics. Despite having different mechanisms of action, the drugs are able to reduce potassium excretion from the body. Hence, both ACEI and potassium-sparing diuretics have the side effect of hyperkalemia. When two drugs are used together, the risk of having hyperkalemia is doubled. Since hyperkalemia has the potential to cause arrhythmia and metabolic acidosis, the combination of ACEI and potassium-sparing diuretics is avoided.