Gabapentin and supplements: interactions, cautions, and safe stacks
Gabapentin is excreted unchanged by the kidneys and has no CYP-mediated metabolism. That removes most of the supplement interactions you would worry about with anti-epileptics like phenytoin, carbamazepine, or valproate. The dominant pharmacokinetic concern is at the absorption step: gabapentin uses the saturable L-amino acid transporter (LAT-1), and its absorption is reduced when divalent cations are present in the gut.
Avoid combiningAvoid
Kava (high-dose extract) combines additive CNS sedation with kava's known hepatotoxicity. Either issue on its own is manageable; combined they are not. Several countries have restricted high-extract kava products; the combination with any CNS-active prescription deserves the strongest caution rather than being treated as a mild additive issue. PMID 38025741; FDA Consumer Advisory 2002
Caution / dose-separate or watch closelyCaution
Magnesium-containing supplements (magnesium glycinate, citrate, oxide; magnesium-containing antacids) reduce gabapentin AUC by approximately 20% via chelation when co-ingested. The fix is timing, not avoidance: separate gabapentin and magnesium dosing by at least 2 hours. PMID 8902323; Neurontin FDA label
Oral calcium supplements and calcium-containing antacids have the same chelation effect. Same 2-hour dose separation rule. Neurontin FDA label
Iron (ferrous sulfate, ferrous bisglycinate, heme iron) chelates gabapentin similarly. Separate dosing by 2 hours. Iron also has its own absorption considerations (best with vitamin C, away from coffee/tea), so coordinating both rules takes some planning. PMID 8902323
CBD (cannabidiol) at neurological doses causes additive sedation and may potentiate gabapentin's effects beyond what either produces alone. Case reports of excessive somnolence in combination, particularly in elderly patients. PMID 38025741
Valerian root adds modest sedation; clinically relevant in elderly patients on gabapentin (fall risk) and at higher valerian extract doses. PMID 38025741
Watch (mild signals)Watch
Melatonin at standard supplement doses (0.3–3 mg) is generally fine with gabapentin. Higher doses (5–10 mg) compound CNS sedation and increase fall risk in elderly patients. Newer "extended release" or high-strength melatonin should be discussed with the prescriber. PMID 38025741
Vitamin B6 (pyridoxal-5-phosphate) is depleted by carbamazepine and phenytoin but not meaningfully by gabapentin — long-term gabapentin patients do not need routine B6 supplementation unless there is another reason for it. Manufacturer label
Often supportive / no problematic interactionSafe
St John's wort does not interact with gabapentin pharmacokinetically — gabapentin is not CYP-metabolised. The general anti-epileptic-class caution about St John's wort does not apply here. (If you are on gabapentin and a CYP-metabolised antidepressant, the St John's wort warning still applies to the antidepressant — see the sertraline page for an example.) Manufacturer label
Mechanism — why gabapentin is different from other anti-epileptics
Gabapentin's pharmacokinetics are structurally different from those of phenytoin, carbamazepine, valproate, and lamotrigine. Three features dominate the interaction profile:
- No CYP metabolism. Renal excretion unchanged. This removes the major class of supplement interactions (St John's wort induction, grapefruit/berberine/piperine inhibition) that drives most anti-epileptic concerns.
- Saturable LAT-1 absorption. Bioavailability is ~60% at 300 mg single dose and drops to ~35% at 1200 mg. Dose-splitting (3 times daily rather than once) improves total absorption and explains the standard TID dosing schedule.
- Cation chelation. Divalent and trivalent cations (Mg²⁺, Ca²⁺, Al³⁺, Fe²⁺/Fe³⁺) bind gabapentin in the gut and reduce absorption. The effect is real but manageable with timing: separate dosing by 2 hours.
The other half of gabapentin's interaction story is purely pharmacodynamic: any sedative supplement (kava, valerian, melatonin, CBD) adds to gabapentin's own CNS depression. This is dose-dependent and matters most in elderly patients, where fall risk is the dominant downstream harm.
Practical dosing notes
The simplest workable schedule for a patient on gabapentin TID plus a magnesium or calcium supplement: take gabapentin with breakfast, lunch, and dinner; take magnesium/calcium with the bedtime snack or first thing in the morning, separated by at least 2 hours from any gabapentin dose. Iron supplementation usually fits well at mid-morning (away from breakfast caffeine and away from gabapentin doses by 2+ hours).
If you've been taking magnesium concurrently with gabapentin for some time and your pain or seizure control feels suboptimal, this absorption issue is worth a one-line question to your prescriber — a small dose adjustment or just better dose timing can recover the missing 20%.
Related class context
Gabapentin's "no CYP" profile differs sharply from valproate, lamotrigine, carbamazepine, and phenytoin — those all interact with St John's wort, grapefruit, and many other CYP-modulating supplements. Pregabalin (Lyrica) has the same α2δ mechanism and similar non-CYP absorption profile, so the rules on this page largely transfer. See the anti-epileptic class overview for the broader comparison.
Sources
- Pfizer. Neurontin (gabapentin) prescribing information. US FDA label, accessed 2026-05. (Divalent-cation absorption rule; CYP-independent metabolism.)
- Stewart BH, et al. A saturable transport mechanism in the intestinal absorption of gabapentin is the underlying cause of the lack of proportionality between increasing dose and drug levels in plasma. PMID: 8902323.
- Asadi-Pooya AA, et al. Drug interactions in epilepsy: a focused review of herbal and supplement co-therapy. PMID: 38025741.
- US Food and Drug Administration. Consumer advisory: kava-containing dietary supplements may be associated with severe liver injury, 2002.
- Russmann S, et al. Kava hepatotoxicity: comparison of aqueous, ethanolic, acetonic kava preparations and kava-herb mixtures. (Hepatotoxicity contextual reference.)
- Brown JD, Winterstein AG. Potential adverse drug events and drug–drug interactions with medical and consumer cannabidiol (CBD) use. (Additive sedation context.)
Educational reference, not medical advice. Gabapentin discontinuation should be gradual to avoid withdrawal seizures. Confirm any supplement change with your prescriber before acting on this page.