What happens to lithium levels in blood when used with hydrochlorothiazide?
(Refer: Katzung’s Basic and Clinical Pharmacology, 10thedition,pg no: 244)

Thiazide diuretics act by inhibiting the NaCl channel of DCT resulting in increased solute loss in urine without affecting the negative free water clearance.
This loss of solutes especially sodium is compensated by increased reabsorption in the PCT.
Renal lithium excretion is affected by changes in the sodium balance.
Drugs causing renal loss of sodium causes increased reabsorption of lithium in PCT.
Eg: ACE inhibitors, AT2 receptor blockers, NSAIDS, Thiazides
Blood levels of lithium rise
Blood levels of lithium decrease
Blood levels of hydrochlorothiazide rise
Blood levels of hydrochlorothiazide fall