May reduce diuretic, natriuretic, & antihypertensive effects w/ NSAIDs (ie, ASA at anti-inflammatory dosage regimens, COX-2 inhibitors, & non-selective NSAIDs). Telmisartan: Dual blockade of the renin-aldosterone system (RAAS) w/ aliskiren. Reversible increase in serum conc & toxicity of lithium. Hydrochlorothiazide: Thiazide-induced hypokalaemia or hypomagnesaemia favors the onset of digitalis-induced arrhythmia. May enhance hyperglycaemic effects of β-blockers & diazoxide. May increase bioavailability w/ anticholinergic agents (eg, atropine, biperiden). May aggravate orthostatic hypotension w/ alcohol, barbiturates, narcotics, or antidepressants.