Lithium

Prescription lithium has a narrow therapeutic window; the effective dose sits uncomfortably close to the toxic one, so blood levels are monitored regularly. Toxicity causes tremor, nausea, vomiting, confusion, unsteadiness, and in severe cases seizures, kidney injury, and coma. Long-term use requires periodic checks of kidney and thyroid function, since lithium can suppress the thyroid and, over years, stress the kidneys; dehydration and certain drugs (NSAID pain relievers, some blood-pressure medicines) can push levels dangerously high. Low-dose or trace forms are far gentler, but any sustained supplementation is worth discussing with a clinician. Not medical advice.

Lithium has well-documented pharmacokinetic interactions centered on renal clearance; the drug is removed from the body almost exclusively by the kidneys, so any medication that affects glomerular filtration or renal tubular ion transport can alter lithium elimination and potentially cause toxicity ^[5]. Nonsteroidal anti-inflammatory drugs (NSAIDs) reduce renal lithium clearance and can raise serum lithium concentrations by 20 to 50%; this effect varies among different NSAIDs but represents a genuine pharmacokinetic risk.

Thiazide diuretics are the most notorious interactants, often increasing lithium levels by 25 to 40 percent; this occurs because thiazides reduce sodium excretion in the proximal tubule, and lithium reabsorption increases in parallel. Angiotensin-converting enzyme (ACE) inhibitors also impair lithium elimination and can precipitate toxicity, though the risk appears lower than with thiazides. Loop diuretics and osmotic diuretics have minor or opposite effects (tending to increase lithium clearance). Interactions not well studied include most antibiotics, most antihistamines, and combination use with selective serotonin reuptake inhibitors as a class, despite their common concurrent prescription in clinical practice.

Checking a whole stack? Run it through interactions + stacks.