FDA’s New Warning: Link of Carbidopa/Levodopa to Vitamin B6 Deficiency and Seizures
On March 20, 2026, the U.S. Food and Drug Administration (FDA) issued a safety warning that requires products containing carbidopa/levodopa to carry new labeling which warns about the potential for Vitamin B6 (pyridoxine) deficiency. The warning guides physicians and other health care professionals to test for baseline vitamin B6 levels (with a blood test) prior to starting patients on treatment with carbidopa/levodopa therapies and periodically while on treatment and to supplement with vitamin B6 as necessary. Of note – it is important that patients do not take vitamin B6 on their own without monitoring blood levels, since vitamin B6 levels that are too high can be dangerous as well.
Carbidopa/Levodopa
Carbidopa/levodopa combinations are the most commonly used treatments for the motor symptoms of Parkinson’s disease (PD) such as tremors, stiffness, and slowed movement. Levodopa is converted into dopamine in the brain to aid in the replenishment of that neurotransmitter which is depleted in PD patients. Carbidopa enhances this effect by preventing levodopa from breaking down before it reaches the brain. These medications are widely prescribed for PD patients due to their effectiveness, and many rely on them long term to treat the motor symptoms of PD.
What the FDA Found
This decision by the FDA follows a safety review that identified 14 cases of seizures linked to vitamin B6 deficiency in patents taking carbidopa/levodopa. Since thirteen of these cases were identified via submission to the FDA in post-marketing reports, the FDA speculates that there are likely more cases which were not submitted.
In all these cases, patients were taking relatively high doses of levodopa at greater than 1,000 mg per day. Some of these reported cases progressed to severe and/or prolonged seizures, with two reported deaths. An important finding was that many of these patients did not respond to standard anti-seizure medications but did respond to vitamin B6 supplementation.
New Recommendations for Patients and Clinicians
The FDA is advising healthcare professionals to check baseline vitamin B6 levels prior to starting carbidopa/levodopa therapy, and if vitamin B6 is low, to consider vitamin B6 supplementation. In addition, vitamin B6 levels should be monitored periodically during treatment. Besides seizures, deficiency of vitamin B6 can also cause specific skin changes (such as rash, red tongue, and cracks in the corner of the mouth) as well as symptoms of neuropathy, which can manifest as numbness or tingling in the hands and feet.
Most people will not experience low vitamin B6 levels from carbidopa/levodopa and this medication remains an essential part of managing PD symptoms. This additional guidance from the FDA will hopefully identify those who do experience low vitamin B6 levels so that they can be safely corrected by a health care provider.