Increased risk of lithium toxicity. May cause and potentiate orthostatic hypotension when used with alcohol, barbiturates, neuroleptics, narcotics or other antihypertensives. Increased risk of acute renal insufficiency in dehydrated patients when used with systemic NSAIDs or high dose salicylates. May increase risk of hypoglycaemia in patients on concurrent treatment with hypoglycaemic sulfonamides/insulin. Concurrent use with baclofen may potentiate antihypertensive effect. May reduce antihypertensive effect when used with corticosteroids or tetracosactide. Increased risk of hyperkalaemia when used with potassium-sparing diuretics or potassium supplements. May increase hypotensive effect of certain anaesthetic drugs. Increased risk of leucopenia when used with allopurinol, immunosuppressants, procainamide or systemic corticosteoids. Additive hypotensive effect when used with other antihypertensives.