According to a U.K. medical journal, Novartis AG’s two hypertension drugs made by combining Diovan and Tekturna although more effective in lowering blood pressure, may have some life-threatening side effects.

A recent study found that these drugs when taken in combination, at the maximum recommended doses, are more beneficial than when taken separately. However, the combination drug may cause a life-threatening side effect of high blood potassium.

Novartis has disputed these results by claiming that these drugs are no more likely to increase blood potassium levels than when either of the two drugs is taken alone.