Levodopa / Carbidopa (Parkinson's)
Common brand names: Sinemet, Rytary, Duopa, Stalevo
Three nutrients listed against this medication. The most severe is marked critical.
At a glance
One of the three is marked well documented. The other two carry their own evidence levels.
At a glance
- Vitamin B6 (P5P)Critical · Well documented
- Vitamin B12Critical · Moderate evidence
- Folate (5-MTHF)Moderate · Mechanism only, no human trial
Color shows how serious each listed effect is. The label beside it shows how strong the evidence is. The cards below explain each one and show its evidence.
Nutrients it can lower
Mechanism, CRITICAL: B6 accelerates peripheral levodopa conversion, on levodopa MONOTHERAPY, B6 reduces central dopaminergic effect and is CONTRAINDICATED. With carbidopa combination (Sinemet, standard), peripheral conversion is blocked, making B6 safe and beneficial.
Common signs, Monotherapy: reduced drug efficacy. Sinemet: B6 deficiency causes peripheral neuropathy, depression, worsening cognition.
Yahr and Duvoisin (JAMA, 1972; PMID PubMed ID: the permanent number the US National Library of Medicine gives a published paper. Each one links to that paper's record on PubMed. 5067358): pyridoxine reverses the effect of levodopa given as monotherapy. Modern carbidopa-levodopa combinations were designed around this interaction.
B6 is used only with a levodopa-plus-carbidopa combination (Sinemet, Stalevo, Rytary) and is avoided with levodopa alone, because B6 accelerates peripheral decarboxylation of unprotected levodopa. Where it is used, P5P 25–50 mg daily is a range in common use and is not from a trial cited on this row.
Mechanism, Levodopa methylation consumes SAMe, increasing homocysteine An amino acid in the blood that rises when vitamin B12, folate or B6 are low. and depleting B12. B12 deficiency in Parkinson's causes peripheral neuropathy clinically indistinguishable from Parkinson's progression. A dangerous diagnostic confusion.
Common signs, Peripheral neuropathy (mimics Parkinson's worsening), cognitive decline, megaloblastic anemia
Rajabally & Martey (Neurology, 2011; PMID 22049200): in Parkinson's patients, cumulative levodopa exposure correlated with lower vitamin B12 and higher neuropathy risk.
Methylcobalamin was used at 1,000–2,000 mcg sublingual daily, with B12 monitored every 6 months; it is among the most important repletions in Parkinson's disease.
Mechanism, Levodopa methylation consumes folate via the one-carbon cycle. Elevated homocysteine from this pathway is associated with accelerated neurodegeneration in Parkinson's.
Common signs, Elevated homocysteine, cardiovascular risk, cognitive decline, accelerated neurodegeneration
Levodopa is O-methylated by COMT, consuming methyl groups and raising homocysteine (Lamberti et al., Movement Disorders, 2005; PMID 15390046). A direct fall in folate levels has not been shown. The concern is mechanistic.
5-MTHF (methylfolate, the active form) was used at 400 to 1,000 mcg daily. That is what the trials administered. It is not a claim that folic acid fails in people with common MTHFR variants: CDC states those variants process folic acid normally.
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Disclosure
These statements have not been evaluated by the Food and Drug Administration. Any grade on this page describes the strength of published human trial evidence in the populations studied. It is not a recommendation for any individual and is not medical advice. Starting, stopping or changing any supplement or medication is a decision for your physician.
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