Fluoxetine and Lithium interaction
Fluoxetine and Lithium: both prescribing labels flag this combination with the strongest language, such as a contraindication, a boxed warning, or an instruction to avoid it.
Do not combine without a prescriber's guidance. The label language below is the strongest FDA uses.
What the FDA labels say
From the Fluoxetine (Prozac) label · effective 2026-01-08
If concomitant use of PROZAC with other serotonergic drugs is clinically warranted, patients should be made aware of a potential increased risk for serotonin syndrome, particularly during treatment initiation and dose increases ( 5.2 )
If concomitant use of PROZAC with other serotonergic drugs is clinically warranted, inform patients of the increased risk for serotonin syndrome and monitor for symptoms.
Lithium — There have been reports of both increased and decreased lithium levels when lithium was used concomitantly with fluoxetine.
Cases of lithium toxicity and increased serotonergic effects have been reported.
Lithium levels should be monitored when these drugs are administered concomitantly [see Warnings and Precautions ( 5.2 )] .
From the Lithium (Lithium Carbonate) label · effective 2026-06-04
If concomitant use of lithium with other serotonergic drugs is clinically warranted, inform patients of the increased risk for serotonin syndrome and monitor for symptoms.
• Serotonergic Agents: Increased risk of serotonin syndrome when co-administered with lithium.
Serotonergic Drugs Clinical Impact: Concomitant use can precipitate serotonin syndrome.
If serotonin syndrome occurs, consider discontinuation of lithium and/or concomitant serotonergic drugs [see Warnings and Precautions ( 5.6 )] .
The risk is increased with concomitant use of other serotonergic drugs (including selective serotonin reuptake inhibitors, serotonin and norepinephrine reuptake inhibitors, triptans, tricyclic antidepressants, fentanyl, tramadol, tryptophan, buspirone, and St.
Taking more than these two? Interactions stack. Check your whole list at once; it stays in your browser.
Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.