Why this matters
Lithium is cleared almost entirely by the kidneys, and NSAIDs reduce renal blood flow enough to cut that clearance meaningfully. There is no dose adjustment that makes this safe for routine use: the interaction is well established, the therapeutic window for lithium is narrow, and toxicity — tremor, confusion, in severe cases seizures — can develop over days rather than weeks.
In short: NSAIDs reduce renal lithium excretion: they can push it to toxic levels.
What to do at the counter
- Avoid NSAIDs in anyone on lithium. Paracetamol (acetaminophen) is the substitute, and it does not share this mechanism.
- If an NSAID genuinely cannot be avoided — a short, medically supervised course — lithium levels need checking at around day 5-7, not left to the next routine blood test.
- This applies to a single OTC purchase, not just prescribed NSAID courses: someone buying ibuprofen for a headache who happens to mention they are on lithium is exactly the conversation this is for.
Which medicines this covers
NSAIDs
ibuprofen, naproxen, diclofenac, dexketoprofen, ketoprofen, celecoxib, etoricoxib, indomethacin, piroxicam, meloxicam, aceclofenac
Medicine
lithium
Checking a longer medication list, or a pair not listed here? Run it through the full drug interactions checker — it covers the whole list at once, pair by pair.
Frequently asked questions
Is paracetamol definitely safe with lithium?
Yes — it does not share the renal mechanism that makes NSAIDs a problem, and it is the standard first-line analgesic recommendation for anyone on lithium.
How would I even know someone is on lithium?
It rarely comes up unprompted. If a repeat customer is buying ibuprofen or naproxen regularly, or mentions a mood-stabiliser in passing, it is worth a direct question — the interaction is serious enough to justify asking.
Does the same apply to other mood stabilisers, like sodium valproate or lamotrigine?
No — the renal-clearance mechanism is specific to lithium. Valproate and lamotrigine do not carry the same NSAID interaction.