Magnesium (oral salts: citrate, glycinate, oxide, sulfate) × Omeprazole

Here the supplement does not obstruct the drug: the drug drains the patient of magnesium. The label records hypomagnesaemia as an adverse reaction of unknown frequency and warns that the severe form can come with hypocalcaemia and hypokalaemia. It appears after months or years of treatment, by which point nobody links the symptom to the stomach protector.

Cramps and muscle spasms, tremor, palpitations, dizziness, irritability. In severe cases tetany, arrhythmias and seizures. Low serum magnesium usually travels with low potassium and calcium that will not correct until magnesium is replaced.

On long-term proton pump inhibitor therapy, measure serum magnesium before starting and periodically thereafter, especially alongside digoxin or a diuretic. Oral supplementation corrects most mild cases, but severe hypomagnesaemia often resolves only when the inhibitor is withdrawn. Also review whether it is still indicated: many of these courses run on out of inertia.