| ⚠️ Key Safety Summary On March 20, 2026, the FDA issued a Drug Safety Communication requiring new warnings on all carbidopa/levodopa-containing medications for Parkinson’s disease, addressing the risk of vitamin B6 (pyridoxine) deficiency and associated seizures. What the FDA found: 14 confirmed cases of seizures linked to vitamin B6 deficiency in patients on carbidopa/levodopa products, including 2 fatalities. All cases involved levodopa doses exceeding 1,000 mg daily. Latency periods ranged from 23 to 132 months, meaning the problem can develop years into treatment. The seizures are clinically distinctive: they do not respond to standard anti-seizure medications but resolve after vitamin B6 supplementation. In 9 of 9 patients who received B6 supplementation, seizures fully resolved. In some cases, progression to status epilepticus was observed before the diagnosis was made. What is now required: healthcare professionals must evaluate baseline vitamin B6 levels before starting treatment, monitor periodically during treatment, and supplement as needed. If you or someone you care for is on a carbidopa/levodopa medication: do not stop the medication without medical guidance. Report new symptoms (seizures, confusion, numbness, tingling) to your prescriber promptly. |
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Parkinson’s disease affects approximately 1 million Americans and is the second most common neurodegenerative condition in the United States. The cornerstone of pharmacological management is levodopa, which the brain converts to dopamine to compensate for the progressive loss of dopamine-producing neurons. Levodopa is almost always combined with carbidopa, which prevents levodopa from being metabolized in the bloodstream before it reaches the brain, allowing lower and more effective doses.
These medications work well. Many patients take them for years or decades. But a drug safety communication issued by the FDA on March 20, 2026 has established, for the first time with a formal labeling requirement, that the same mechanism that makes carbidopa/levodopa effective is also depleting vitamin B6, and that this depletion can, in some patients, cause seizures that clinicians may not immediately recognize as B6-related.
What the FDA Found: 14 Cases, 2 Deaths, and a Seizure Type That Resists Standard Treatment
The FDA’s safety review identified 14 cases of seizures linked to vitamin B6 deficiency in patients using carbidopa/levodopa products. Thirteen were postmarketing reports submitted to the FDA Adverse Event Reporting System (FAERS) database; one was identified in the medical literature.
Because the FDA notes that its review relied on spontaneous case reports and that similar cases may exist unreported, the 14 confirmed cases likely underestimate the true incidence.
Key characteristics of the 14 cases:
| Feature | Detail |
|---|---|
| Total confirmed cases | 14 |
| All cases: levodopa dose | Above 1,000 mg daily in every case |
| Higher doses (above 1,500 mg) | Associated with shorter time to deficiency development |
| Latency period (treatment start to seizure onset) | 23 to 132 months |
| Seizure type | Focal onset seizures with secondary generalization; some progressed to status epilepticus |
| Response to standard anti-seizure medications | Did not respond in the majority of cases |
| Response to vitamin B6 supplementation | 9 of 9 treated patients had complete resolution |
| Fatalities | 2, both with documented low vitamin B6 levels and poorly controlled seizures |
| Formulations involved | Oral tablets and enteral suspension |
| Cases involving Stalevo or Vyalev | None confirmed, but biological plausibility supports similar risk |
Source: FDA Drug Safety Communication, March 20, 2026.
The status epilepticus finding is the most urgent clinical detail
The FDA communication notes that progression to status epilepticus was observed in some of the reported cases. Status epilepticus is a neurological emergency, defined as a seizure lasting more than five minutes or two or more seizures without full recovery of consciousness between them. It carries significant risk of brain injury and death if not treated rapidly. In the context of this safety communication, the critical clinical implication is that if a patient on carbidopa/levodopa presents with new-onset seizures that do not respond to conventional anti-seizure medications, vitamin B6 deficiency should be in the differential diagnosis immediately, not as a last resort.
The seizure pattern described is consistent with vitamin B6-dependent epilepsy: focal onset seizures with secondary generalization that resist standard anticonvulsants and resolve with pyridoxine. This pattern has a known biochemical mechanism.
The supporting evidence for B6 deficiency in these cases
Beyond the seizures themselves, the FDA review found additional laboratory and clinical evidence of vitamin B6 deficiency in the reviewed cases:
- Elevated homocysteine levels in four cases (B6 is required for homocysteine metabolism; deficiency causes it to accumulate)
- Microcytic or normocytic anemia in three cases (B6 is required for heme synthesis)
- Neuropsychiatric symptoms in four cases
This multi-system evidence of B6 deficiency strengthens the FDA’s conclusion that “there is reasonable evidence of a causal association between drug products containing carbidopa/levodopa and vitamin B6 deficiency-associated seizures.”
Why Carbidopa/Levodopa Depletes Vitamin B6: The Mechanism
Understanding the biochemical basis of this safety signal helps explain both why it is real and why it has been underrecognized.
Vitamin B6 (pyridoxine) is a water-soluble vitamin with a critical role in over 100 enzymatic reactions in the body, particularly in amino acid metabolism and neurotransmitter synthesis. Its active form, pyridoxal-5′-phosphate (PLP), is the biologically active cofactor.
Carbidopa/levodopa depletes B6 through two mechanisms operating simultaneously:
First: The conversion of levodopa to dopamine (and its subsequent metabolism) consumes PLP as a cofactor. At higher levodopa doses, this ongoing metabolic consumption exceeds normal dietary intake and tissue stores.
Second: Carbidopa itself binds to and inactivates pyridoxal phosphate. This is not a side effect unique to therapeutic use. The structural interaction between carbidopa and PLP is well-characterized biochemically, and it was the reason that earlier levodopa formulations without carbidopa actually caused peripheral B6 depletion through a somewhat different pathway.
The combined effect is a functional reduction in available B6 that compounds over time at higher doses. The long latency period (23 to 132 months) reflects this gradual depletion dynamic: it takes time for dietary intake and tissue stores to be overwhelmed.
What Products Are Affected
The new warning requirement applies to all drug products containing carbidopa and levodopa. These include:
| Brand name | Components | Formulation |
|---|---|---|
| Sinemet, Sinemet CR | Carbidopa/levodopa | Oral tablets (immediate and controlled release) |
| Rytary | Carbidopa/levodopa | Oral extended-release capsules |
| Dhivy | Carbidopa/levodopa | Oral tablets |
| Crexont | Carbidopa/levodopa | Oral extended-release capsules |
| Duopa | Carbidopa/levodopa | Enteral suspension (continuous infusion) |
| Stalevo | Carbidopa/levodopa/entacapone | Oral tablets |
| Vyalev | Foscarbidopa/foslevodopa | Subcutaneous infusion |
No confirmed cases of B6-deficiency seizures were found with Stalevo or Vyalev, which the FDA attributes to lower usage patterns, more recent approval dates, and different dosing requirements. However, the FDA explicitly states that biological plausibility supports similar risk across all formulations, noting that vitamin B6 deficiency was observed in the clinical trials for the injectable product. The warning applies to all formulations.
For Patients and Caregivers
Do not stop your medication without speaking to your neurologist or prescriber first
Carbidopa/levodopa is essential for managing Parkinson’s symptoms. Stopping abruptly can cause serious problems including a Parkinson’s crisis (sudden, severe worsening of symptoms), and in rare cases, a potentially life-threatening condition called neuroleptic malignant-like syndrome from abrupt withdrawal. The solution to B6 depletion is monitoring and supplementation, not stopping the medication.
What to watch for and report to your doctor immediately
Contact your prescriber promptly if you experience any of the following:
- New or unexplained seizures of any kind
- Confusion or worsening cognitive symptoms
- Depression that seems different from your baseline
- Numbness, tingling, sharp pains, or weakness in the hands, feet, or limbs
- Mouth sores, inflammation of the tongue or lips, or skin changes
- Persistent fatigue
If a seizure occurs and does not respond to emergency anti-seizure treatment, inform emergency responders and hospital staff that you are taking carbidopa/levodopa and that vitamin B6 deficiency-associated seizures should be considered. The seizures described in the FDA cases did not respond to conventional anticonvulsants but resolved with B6 supplementation.
Ask your provider about monitoring
Based on the new FDA warning, your prescriber should now:
- Check your vitamin B6 level before starting or continuing treatment (particularly if you have been on levodopa for a long time or are on high doses)
- Recheck B6 levels periodically during treatment
- Consider whether vitamin B6 supplementation is appropriate for your situation
Do not self-supplement with high-dose B6 without medical guidance. While standard dietary doses of B6 are safe, high-dose pyridoxine supplementation (above 50 to 100 mg per day for extended periods) carries its own risk of peripheral neuropathy and should be managed by your provider.
Resources for people living with Parkinson’s disease
The Parkinson’s Foundation and the Michael J. Fox Foundation for Parkinson’s Research both maintain current patient-facing information on Parkinson’s medications, including updates on drug safety communications. The FDA’s safety communication page is updated as new information becomes available.
For Healthcare Professionals
The FDA’s new labeling requirement translates to the following clinical actions:
| When | Action |
|---|---|
| Before starting carbidopa/levodopa | Evaluate baseline vitamin B6 (pyridoxine) and PLP levels |
| Periodically during treatment | Recheck B6 levels, frequency guided by dose and clinical status |
| If new symptoms appear | Evaluate B6 levels promptly regardless of time on therapy |
| If seizures occur | Recognize that B6 deficiency-associated seizures do not respond to standard anticonvulsants; vitamin B6 administration is the treatment |
| When titrating to doses above 1,000 mg levodopa | Higher vigilance warranted; doses above 1,500 mg levodopa associated with shorter time to deficiency |
| If adding anti-seizure medications | Be aware that select anticonvulsants can worsen B6 deficiency |
The seizure type is distinctive and should be recognized: focal onset with secondary generalization, consistent with pyridoxine-dependent epilepsy, unresponsive to conventional anticonvulsants, and resolving with B6 administration. Elevated homocysteine, microcytic or normocytic anemia, and neuropsychiatric symptoms are supporting laboratory findings that can help confirm the diagnosis when seizures occur in the context of carbidopa/levodopa use.
Reporting Adverse Events
Patients and healthcare professionals should report adverse events related to carbidopa/levodopa products to the FDA MedWatch program online at fda.gov/safety/medwatch or by calling 1-800-332-1088. Reporting contributes to the pharmacovigilance database that identifies safety signals like this one. The FDA’s 14-case dataset almost certainly undercounts the true incidence of this adverse effect; reporting by clinicians who encounter it helps the agency characterize the full scope.
For related coverage of drug safety communications and post-market safety monitoring on Health Evidence Digest, see our post on the Tavneos (avacopan) serious liver injury warning and what it means when the FDA and a manufacturer disagree about risk and our analysis of why the FDA required post-marketing studies for Foundayo after its accelerated approval.
Sources
FDA Drug Safety Communication (primary source): FDA Is Requiring Warning about Vitamin B6 Deficiency and Associated Seizures for Drug Products Containing Carbidopa/Levodopa. March 20, 2026. fda.gov.
FDA DSC PDF: Drug Safety Communication PDF. fda.gov/media/191605.
FAERS reporting system: Questions and Answers: FDA’s Adverse Event Reporting System. fda.gov.
Vitamin B6 (pyridoxine) overview: Vitamin B6: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements.
Homocysteine and B6: Homocysteine. StatPearls. NCBI.
Status epilepticus: Status Epilepticus. StatPearls. NCBI.
Parkinson’s disease overview: Parkinson’s Disease. NINDS.
Levodopa withdrawal syndrome: Neuroleptic Malignant Syndrome and Parkinsonism-Hyperpyrexia. StatPearls. NCBI.
MedWatch reporting: FDA MedWatch. fda.gov/safety/medwatch.
Patient resources: Parkinson’s Foundation | Michael J. Fox Foundation
| Disclaimer: Health Evidence Digest provides general information about FDA drug safety communications and health research for educational purposes. This content is not a substitute for professional medical advice. Patients taking carbidopa/levodopa-containing medications should not discontinue treatment without consulting their neurologist or prescribing clinician. Report new symptoms to your healthcare provider. |
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