FDA Warns: Carbidopa/Levodopa Can Cause Vitamin B6 Deficiency — and Seizures

Carbidopa/levodopa is one of the main treatments used to control the movement symptoms of Parkinson's disease.

Levodopa is converted into dopamine, helping replace some of the dopamine that is lost as Parkinson's progresses.

But the chemistry of these drugs can also affect vitamin B6.

Vitamin B6 is involved in the conversion of levodopa to dopamine. Carbidopa also binds to pyridoxal 5'-phosphate (PLP), the active coenzyme form of vitamin B6.

The result can be reduced vitamin B6 availability.

Higher doses of carbidopa/levodopa may increase the risk of deficiency.

The FDA conducted a safety review after reports of seizures in people taking carbidopa/levodopa.

It identified 14 cases of seizures linked to vitamin B6 deficiency.

Thirteen were reported to the FDA's adverse-event reporting system and one came from the medical literature.

The FDA says there are likely additional cases that were not identified.

All 14 reviewed cases involved more than 1,000 mg of levodopa per day.

That's the levodopa component—not the combined weight of the carbidopa/levodopa tablet.

For example, someone taking ten 25/100 mg carbidopa/levodopa tablets in a day would receive 1,000 mg of levodopa.

The FDA found that doses above 1,500 mg of levodopa were associated with a shorter time from starting treatment to identifying vitamin B6 deficiency.

The reported time between starting treatment and identifying the deficiency ranged from 23 to 132 months.

These were not routine clinical-trial findings. They were postmarketing reports and published case evidence, so they cannot tell us how often this complication occurs among everyone taking carbidopa/levodopa.

That is an important limitation.

This is one of the more striking parts of the FDA review.

Many of the reported seizures did not respond to traditional anti-seizure medications but resolved after vitamin B6 was administered.

Of the nine patients who received vitamin B6 supplementation, all nine had resolution of their seizures.

The majority had previously shown a lack of response to multiple anti-seizure medications.

Two people in the FDA's review died. Both had documented low vitamin B6 levels and poorly controlled seizures.

The FDA concluded that there was reasonable evidence of a causal association between carbidopa/levodopa products and vitamin B6-deficiency-associated seizures.

That is why the warning is strong.

But the number of reported cases cannot tell us the actual frequency of the problem.

There's another wrinkle worth knowing about.

The FDA notes that some anti-seizure medications can further worsen vitamin B6 deficiency.

That matters because several of the patients in the reported cases had already been treated with multiple anti-seizure medications.

This does not erase the FDA's finding. In fact, the resolution of seizures after vitamin B6 supplementation provides important evidence supporting B6 deficiency as part of the problem.

But it does mean these cases can be medically complicated.

A person with Parkinson's who develops seizures may have several possible contributing factors, and doctors need to look at the entire medication and nutritional picture rather than assuming there is only one cause.

The FDA says vitamin B6 deficiency can also produce other symptoms.

These include:

• Numbness
• Tingling
• Sharp nerve pain
• Muscle weakness
• Depression
• Confusion
• Inflammation of the lips
• Inflammation of the tongue
• Skin inflammation
• Anemia
• Seizures

The neurological symptoms are particularly relevant because neuropathy can have multiple causes in someone with Parkinson's disease.

New or worsening nerve symptoms shouldn't automatically be assumed to be “just Parkinson's.”

Here's a wrinkle that is easy to miss.

Vitamin B6 deficiency isn't the only B6-related problem.

Too much vitamin B6 can also cause peripheral neuropathy.

That means someone who develops tingling or numbness shouldn't simply conclude that they need to start taking a large dose of B6.

The goal is to determine what's actually happening.

A 2023 systematic review examined abnormal vitamin B6 levels in people living with Parkinson's disease.

Across the studies included in the review, abnormal B6 levels were reported in 60 of 145 people, although the underlying studies were small and heterogeneous.

Low B6 was reported in 52 people and high B6 in eight.

Low B6 was reported particularly often among people receiving levodopa/carbidopa, including both oral treatment and intestinal-gel treatment.

In almost all studies reporting low B6 among people receiving oral levodopa/carbidopa, the levodopa dose was at least 1,000 mg per day.

The authors emphasized that better epidemiological research is needed to establish how common abnormal B6 levels actually are and what they mean clinically.

A 2026 scoping review looked specifically at the direct evidence concerning vitamin B6 depletion during carbidopa/levodopa treatment.

The researchers identified 36 reports meeting their criteria, including human studies and case reports or case series.

They found that lower B6 biomarkers appeared most consistently with high or rapidly increased exposure, but the findings were not uniform.

Other factors—including dose, route of administration, advanced Parkinson's disease, nutrition and vitamin supplementation—could not always be separated.

The review concluded that no study has yet established:

• The population-level incidence of B6 depletion
• A definite clinical risk threshold
• The ideal testing interval
• Or a universal preventive B6 dose

The researchers said direct vitamin B6 testing, interpreted alongside the patient's nutritional, blood and neurological picture, is better supported than relying on a single indirect marker such as homocysteine.

That's a useful reality check.

The FDA warning is real.

The causal signal is meaningful.

But science still doesn't know exactly how common this complication is or precisely who is most vulnerable.

A 2025 case report described an adult with Parkinson's disease who developed new seizures that were resistant to multiple anti-seizure medications after a recent increase in carbidopa/levodopa.

The patient was found to have vitamin B6 deficiency.

The seizures resolved after pyridoxine supplementation, and the patient was subsequently able to discontinue the anti-seizure medications without further seizures.

A single case cannot establish how common the problem is.

But it adds to the pattern that prompted the FDA warning.

And there are earlier published case reports describing similar problems in people with Parkinson's receiving carbidopa/levodopa, particularly at high doses.

The most important point is simple:

Don't stop your Parkinson's medication on your own.

Abruptly reducing or stopping levodopa can cause serious problems.

Instead, the FDA recommends that healthcare professionals evaluate vitamin B6 levels:

• Before starting carbidopa/levodopa
• Periodically during treatment
• And when symptoms suggesting vitamin B6 deficiency appear

The FDA says healthcare professionals should consider vitamin B6 supplementation when necessary.

So if you take carbidopa/levodopa, a reasonable question to ask your healthcare professional is:

“Should my vitamin B6 level be checked?”

That question may be particularly relevant if you take a high dose, recently increased your dose, have nutritional problems, or have developed unexplained neurological symptoms.

And if you have a new seizure, that's an urgent medical problem regardless of its suspected cause.

The FDA warning applies to drug products containing carbidopa/levodopa.

These include products such as:

• Crexont
• Dhivy
• Duopa
• Rytary
• Sinemet
• Sinemet CR
• Stalevo
• Vyalev

These products come in different formulations, including oral medications, intestinal suspension and continuous subcutaneous infusion.

The FDA did not identify reported B6-deficiency-associated seizures in its review involving carbidopa/levodopa/entacapone products or the injectable carbidopa/levodopa product.

However, the FDA said biological plausibility suggests the risk could potentially apply across carbidopa/levodopa products, and vitamin B6 deficiency was also observed in clinical trials involving the injectable product.

That's an important distinction:

No reported cases in the FDA review does not mean no possible risk.

It's a better question:

“Could vitamin B6 deficiency be contributing to what's happening to me?”

That's especially worth discussing if you're taking carbidopa/levodopa and experience:

• A new seizure
• Unexplained numbness or tingling
• New or worsening nerve pain
• Muscle weakness
• Other unexplained neurological changes

A healthcare professional can decide whether B6 testing or supplementation makes sense.

And remember:

More B6 isn't automatically better.

High doses of B6 can themselves cause nerve damage.

The FDA has issued a new safety warning that carbidopa/levodopa can cause vitamin B6 deficiency and B6-deficiency-associated seizures. The FDA identified 14 seizure cases in its review, all involving more than 1,000 mg of levodopa per day. Nine patients who received B6 supplementation had their seizures resolve.

That provides a meaningful causal signal.

But these were postmarketing reports and case evidence, so we don't know how frequently this complication occurs among people taking carbidopa/levodopa.

The warning also matters for people experiencing new or worsening neuropathy—such as numbness, tingling, sharp pain or weakness.

The important message isn't to stop Parkinson's medication or start taking large amounts of vitamin B6 on your own.

It's to know that B6 deficiency is now an FDA-recognized potential complication of carbidopa/levodopa treatment and that it may be worth checking when the symptoms fit.

Sometimes the most useful medical information isn't a new treatment.

It's knowing what question to ask when something doesn't make sense.