Sertraline and Phenytoin: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jul 2, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Phenytoin
Sertraline
No brand names on record
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
Taking phenytoin (Dilantin) and sertraline together can push things in two directions. Sertraline can slow down how your body breaks down phenytoin, so phenytoin levels can climb. Because phenytoin is a seizure medicine with a narrow safe range, even a small rise can cause side effects like dizziness, unsteady walking, slurred speech, drowsiness, or double vision.
At the same time, phenytoin can speed up how your body clears sertraline, so your antidepressant may not work as well. The good news is your care team can manage this. They may check your phenytoin blood levels and adjust doses as needed. Please don't stop or change either medicine on your own, just tell your doctor or pharmacist.
Effect: Increased phenytoin exposure (toxicity risk) and reduced sertraline efficacy. Neither drug is a prodrug; interpret as bidirectional.
- Mechanism: Sertraline inhibits CYP2C9/CYP2C19-mediated phenytoin metabolism, raising phenytoin levels. Phenytoin is a potent CYP inducer that accelerates sertraline metabolism, lowering its levels/effect.
- NTI: Phenytoin has a narrow therapeutic index; small PK changes are clinically meaningful.
- Evidence: Probable; elevated phenytoin levels reported in 2 elderly patients.
- Management: Monitor phenytoin serum levels when starting/titrating sertraline; reduce phenytoin dose if needed. Adjust both agents when phenytoin is added or withdrawn. Watch for loss of antidepressant response.
What happens
Increased risk of phenytoin toxicity and reduced efficacy of sertraline
Interaction Deep Dive
Using phenytoin, which acts as a substrate for CYP2C9 and CYP2C19 as well as a strong inducer of CYP enzymes, together with sertraline can heighten the likelihood of phenytoin toxicity while diminishing the effectiveness of sertraline34. In 2 elderly patients, giving phenytoin alongside sertraline led to raised serum phenytoin concentrations5. For the best clinical results, dose modifications of both phenytoin and sertraline should be considered whenever phenytoin is introduced into or removed from a patient's therapy. Monitoring of phenytoin serum drug levels is advised34 when sertraline is started or its dose is adjusted. If necessary, lower the phenytoin dose1.
Why it happens (mechanism)
Inhibition of CYP-mediated phenytoin metabolism by sertraline; induction of CYP-mediated sertraline metabolism by phenytoin
How to manage this interaction
Your care team can manage this combination safely with monitoring and individualized dosing.
- Keep taking both exactly as prescribed unless your doctor tells you otherwise.
- Your team may check phenytoin blood levels when sertraline is started or its dose is changed, and adjust the phenytoin dose if needed.
- Doses of both medicines may need to be adjusted and individualized whenever phenytoin is added or stopped.
- Tell your doctor if you feel dizzy, unsteady, very drowsy, or notice double vision or slurred speech (possible phenytoin toxicity), or if your mood symptoms seem to return.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
2 reports — tap to read
a) Two elderly patients experienced raised serum phenytoin concentrations while receiving sertraline concurrently. Patient 1, a 78-year old man, was taking phenytoin 300 mg per day along with several other medications. When sertraline 25 mg every night was introduced to treat depression, his serum phenytoin concentration rose from 5.2 mcg/mL to 12.3 mcg/mL. Following stepwise increases in the sertraline dose to 75 mg per day, the patient's serum phenytoin concentration climbed to 30.9 mcg/mL. Phenytoin was stopped but was subsequently reinstated successfully at 200 mg per day. Sertraline 100 mg per day was likewise given without any further adverse effects. Patient 2, an 85-year old man, showed rising serum phenytoin concentrations (from 15.6 mcg/mL to 20 mcg/mL) after sertraline 25 mg every other day was added to phenytoin 260 mg per day. The authors advise measuring serum phenytoin concentrations within one week of beginning sertraline therapy or making a change to the sertraline dose 5.
b) Sertraline is recognized as a moderate to weak inhibitor of the CYP2D6 isoenzyme and is thought to inhibit the CYP2C9 and CYP3A4 hepatic isoenzymes. Phenytoin metabolism may involve the CYP2D6 6 and CYP2C9 hepatic isoenzymes 72.
Common questions
Can I take Sertraline and Phenytoin together?
Combining phenytoin and sertraline can raise phenytoin levels (toxicity risk) while weakening sertraline's effect; your care team can manage this by checking phenytoin blood levels and adjusting doses, so keep taking both as prescribed and report new side effects. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Sertraline and Phenytoin interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How is the Sertraline and Phenytoin interaction managed?
Your care team can manage this combination safely with monitoring and individualized dosing. Keep taking both exactly as prescribed unless your doctor tells you otherwise. Your team may check phenytoin blood levels when sertraline is started or its dose is changed, and adjust the phenytoin dose if needed. Doses of both medicines may need to be adjusted and individualized whenever phenytoin is adde… Management is individual — always follow your own care team's guidance.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Sertraline or Phenytoin need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (7)
- Product Information: ZOLOFT oral tablets, oral solution, sertraline hydrochloride oral tablets, oral solution. Viatris Specialty LLC (per FDA), Morgantown, WV, 2023. DailyMed
- DeVane CL: Pharmacokinetics of the newer antidepressants: clinical relevance. Am J Med 1994; 97(suppl 6A):13S-23S. PubMed
- Product Information: Dilantin(R) intravenous injection, intramuscular injection, phenytoin sodium intravenous injection, intramuscular injection. Parke-Davis (per FDA), New York, NY, 2013. DailyMed
- Product Information: Dilantin-125(R) oral suspension, phenytoin oral suspension. Parke-Davis (per FDA), New York, NY, 2013. DailyMed
- Haselberger MB, Freedman LS, & Tolbert S: Elevated serum phenytoin concentrations associated with coadministration of sertraline. J Clin Psychopharmacol 1997; 17:107-109. PubMed
- Murray M: P450 enzymes: inhibition mechanisms, genetic regulation and effects of liver disease. Clin Pharmacokinet 1992; 23:132-146.
- Riesenman C: Antidepressant drug interactions and the cytochrome P450 system: a critical appraisal. Pharmacotherapy 1995; 15(6 part 2):84S-99S. DOI
Keep reading about Phenytoin
Keep reading about Sertraline
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