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[Biochemistry](https://durgical.com/en/biochemistry/) · Molecule

# L-DOPA (levodopa)

L-DOPA is the first product of catecholamine synthesis. Given as levodopa, it crosses into the brain and replaces dopamine in Parkinson disease.

Updated 2026-11-01

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## Key facts

- Made from tyrosine by tyrosine hydroxylase (BH4), the rate-limiting step of catecholamine synthesis.
- Unlike dopamine, it crosses the blood–brain barrier on the large neutral amino acid carrier.
- AADC (B6) decarboxylates it to dopamine; carbidopa blocks this outside the brain.
- In melanocytes tyrosinase also makes L-DOPA on the way to melanin.

**Also called**
3,4-Dihydroxyphenylalanine

**Formula**
C₉H₁₁NO₄

**PubChem**
[CID 6047](https://pubchem.ncbi.nlm.nih.gov/compound/6047)

## Structure

- Tyrosine with a second hydroxyl on the ring: a catechol (3,4-dihydroxyphenyl) amino acid.

## Clinical notes

- Levodopa with carbidopa is the most effective treatment for the motor signs of Parkinson disease.
- Protein-rich meals compete with levodopa for absorption and brain entry.
- Dopa-responsive dystonia (tyrosine hydroxylase or GTP cyclohydrolase defects) improves dramatically with levodopa.

## Pathways

- [Catecholamine synthesis and breakdown](https://durgical.com/en/biochemistry/pathways/catecholamine-synthesis-and-breakdown/)

## Related conditions

- [Parkinson disease](https://durgical.com/en/conditions/parkinson-disease/)
- [Oculocutaneous albinism](https://durgical.com/en/conditions/oculocutaneous-albinism/)

## Related

- [Tyrosine](https://durgical.com/en/biochemistry/molecules/tyrosine/)
- [Tyrosine hydroxylase](https://durgical.com/en/biochemistry/enzymes/tyrosine-hydroxylase/)
- [Dopamine](https://durgical.com/en/biochemistry/molecules/dopamine/)
- [Tetrahydrobiopterin (BH4)](https://durgical.com/en/biochemistry/molecules/tetrahydrobiopterin/)
- [Vitamin B6 (pyridoxal phosphate)](https://durgical.com/en/biochemistry/molecules/vitamin-b6/)

## Test yourself

Think of the answer, then tap the question to see it.

## Why is Parkinson disease treated with levodopa rather than dopamine?

Dopamine does not cross the blood–brain barrier; levodopa does and is decarboxylated to dopamine in the brain.

## Which enzyme makes L-DOPA, and what cofactor does it need?

Tyrosine hydroxylase, which needs tetrahydrobiopterin (BH4), Fe²⁺ and O₂.

## What does carbidopa do?

It blocks DOPA decarboxylase outside the brain, so more levodopa reaches the brain.

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Molecules are shown in their neutral form, as the databases deposit them; in the cell the acids and phosphates are ionised.

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Levodopa (CID 6047)](https://pubchem.ncbi.nlm.nih.gov/compound/6047) (PubChem, NCBI, 2026) · Public domain; [TH gene: MedlinePlus Genetics](https://medlineplus.gov/genetics/gene/th/) (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/biochemistry/molecules/l-dopa/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/molecules/l-dopa/