SeriousCaution
Melatonin
Melatonin can add to phenobarbital sedation and psychomotor impairment.
Recommendation: Avoid or use only with prescriber guidance; do not drive if impaired.
Phenobarbital
Prescription ·Strong evidence ·Reviewed May 2026
Phenobarbital is a long-acting barbiturate used for seizure disorders and, less commonly, sedative indications. It is habit-forming, can cause respiratory depression and profound sedation, and abrupt withdrawal after chronic use can precipitate seizures or death. Chronic enzyme induction can lower vitamin D and folate status and contribute to bone disease.
What it's good for
- Long-term seizure prevention in selected generalized or focal seizure disorders2
- Neonatal seizure management in specialist settings
- Sedative-hypnotic use is now limited because safer alternatives usually exist
What to watch for
- Sedation
- Cognitive slowing
- Ataxia
- Hypersensitivity to barbiturates
- Manifest or latent porphyria2
The bottom line
Evidence rating strong. Most-documented uses: long-term seizure prevention in selected generalized or focal seizure disorders, neonatal seizure management in specialist settings, sedative-hypnotic use is now limited because safer alternatives usually exist. 3 sources indexed (1968–2025), with 4 interaction records on file.
The science
How it works, mechanistically.
Core mechanism
Phenobarbital enhances GABA-A receptor-mediated inhibitory neurotransmission, mainly by prolonging chloride-channel opening, and at higher concentrations can reduce excitatory glutamate transmission. It is a strong inducer of hepatic drug-metabolizing enzymes, including CYP pathways and UGTs. Enzyme induction accelerates vitamin D catabolism and can reduce folate status, contributing to osteomalacia, low bone mineral density, and megaloblastic changes during prolonged therapy.1,2
Class
Barbiturate anticonvulsant
Dosing
Dosing & protocol.
Common range
Adult anticonvulsant maintenance is commonly 60-200 mg/day individualized by response and serum levels; sedative dosing is lower and indication-specific.
Recommended form
Oral tablet or elixir for maintenance; injectable formulation in acute or inpatient settings
Can be taken with or without food. Avoid alcohol and other CNS depressants unless specifically supervised.
Depletions
What it depletes.
Nutrients this medication can lower over time, and what to replace.
Vitamin D
SignificantPhenobarbital induces hepatic enzymes that accelerate vitamin D catabolism, lowering 25-hydroxyvitamin D and reducing calcium absorption.
Replace Vitamin D3Monitor Serum 25-hydroxyvitamin DOnset Months to years of chronic therapy, with higher risk when intake or sunlight exposure is low
Calcium
ModerateReduced vitamin D activity decreases intestinal calcium absorption and can contribute to secondary hyperparathyroidism and bone loss.
Replace CalciumMonitor Serum calcium, parathyroid hormone, and bone density when indicatedOnset Months to years, usually secondary to vitamin D disruption
Folate
ModerateChronic enzyme-inducing anticonvulsant therapy can lower folate status through altered metabolism and absorption, increasing risk of megaloblastic changes.
Replace MethylfolateMonitor CBC, serum folate, red blood cell folate, and homocysteineOnset Months to years of long-term therapy
Safety
Full safety detail.
Side effects
- Sedation
- Cognitive slowing
- Ataxia
- Dizziness
- Respiratory depression at high doses or with sedatives
- Dependence and withdrawal seizures
- Depression or behavioral changes
- Rash or hypersensitivity
- Megaloblastic anemia
- Osteopenia or osteomalacia with chronic therapy
- Suicidal thoughts or behavior warning for antiepileptic drugs
Interactions
Interaction records.
ModerateCaution
L-Theanine
L-Theanine may add calming or sedating effects to phenobarbital.
Recommendation: Use cautiously and avoid additional sedatives or alcohol.
ModerateCaution
Ashwagandha
Ashwagandha may be sedating and can compound phenobarbital CNS depression.
Recommendation: Avoid during titration or if sedation is present.
ModerateConflict
Ginkgo Biloba
Ginkgo has seizure case reports and may undermine seizure control.
Recommendation: Avoid ginkgo in patients using phenobarbital for seizures.
Sources
Sources, by evidence tier.
Numbered references. Citations throughout the page link here.
Reviews & position papers
1- 1Antiepileptics and bone healthNeeds reviewNo linkPack AM · Current Opinion in Neurology · 2004
Review links enzyme-inducing antiseizure drugs including phenobarbital with altered vitamin D metabolism and bone disease.
Reference material
2- 2PHENOBARBITAL tablets, US Prescribing InformationNeeds reviewURLU.S. National Library of Medicine · DailyMed · 2025
Labeling describes barbiturate warnings, contraindications, long half-life, and need for periodic laboratory evaluation with prolonged therapy.
- 3Folate deficiency and anticonvulsant therapyNeeds reviewNo linkReynolds EH · Lancet · 1968
Classic clinical literature describes folate lowering during chronic anticonvulsant therapy.
Keep exploring
Deep dives & adjacent profiles.
This page is educational. Do not start, stop, or change a supplement or medication based on it without checking with a qualified healthcare professional.
Use this with your stack
Phenobarbital in NutriStack.
Add it to your stack, see how it interacts with everything else you take, and get a Stack Score that updates the moment it does.