A medicine given with levodopa for Parkinson's disease
Carbidopa
A medicine given together with levodopa in Parkinson's disease that helps more levodopa reach the brain.
What is Carbidopa?
Carbidopa is a medicine used in Parkinson's disease, but it is almost never used on its own. It is given together with levodopa, and its job is to stop levodopa being broken down in the body before it reaches the brain, so that more of it gets to where it is needed and lower doses can be used with fewer side effects such as nausea. By itself carbidopa has little effect on Parkinson's symptoms. The combination can cause nausea, light-headedness when standing up from low blood pressure, and, over time, involuntary movements. It is usually prescribed as a single combination tablet.
Education and reference only. This is a plain-language guide to Carbidopa — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Carbidopa is a medicine used in the treatment of Parkinson's disease, almost always as part of a combination product with levodopa. Levodopa is the medicine that actually replaces the missing brain chemical (dopamine) in Parkinson's, but a lot of it is broken down in the body before it can reach the brain. Carbidopa's role is to protect levodopa from this early breakdown. On its own, carbidopa does very little for Parkinson's symptoms, which is why it is taken alongside levodopa rather than separately. It is usually supplied as a single tablet containing both medicines.
How it works
In Parkinson's disease the brain is short of dopamine, and levodopa is given because the brain can turn it into dopamine. However, an enzyme in the rest of the body converts much of the levodopa into dopamine before it gets to the brain, which both wastes the medicine and causes side effects such as nausea. Carbidopa blocks this enzyme outside the brain, so more levodopa survives to reach the brain, where it can be converted to dopamine and ease the symptoms. Because carbidopa does not cross into the brain itself, it does not interfere with the helpful conversion that happens there.
Company & origin
Originated / developed by: Various manufacturers.
A medicine used in the UK almost always combined with levodopa to treat Parkinson's disease, helping levodopa reach the brain.
What it treats
Conditions Carbidopa is used for
Practical use
How to take Carbidopa
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it as the combination tablet with levodopa, at the regular times your specialist sets, to keep symptoms steady.
- Stand up slowly from sitting or lying down, as the combination can lower blood pressure and cause light-headedness.
- Take it with or after food if it makes you feel sick, but follow any specific advice your team gives about food and protein timing.
- Do not stop the combination suddenly, as this can cause a serious worsening of symptoms; any changes should be guided by your specialist.
- Tell your team about any unusual movements, sudden sleepiness or changes in mood or behaviour.
Weighing it up
Advantages & disadvantages of Carbidopa
Advantages
- Helps more levodopa reach the brain, so it works better in Parkinson's disease.
- Allows lower levodopa doses, which reduces side effects such as nausea.
- Usually given as a single convenient combination tablet.
Disadvantages
- Has little effect on Parkinson's symptoms when taken on its own.
- The combination can cause nausea and a drop in blood pressure with light-headedness on standing.
- Over time, the combination can cause involuntary movements and wearing-off between doses.
Practical use
Good to know
The key thing to understand is that carbidopa is a helper medicine: it makes levodopa work better and with fewer side effects, but it has little effect on Parkinson's by itself, which is why it is given as a combination product. Because the combination works on dopamine, it can cause nausea, especially at first, and it can lower blood pressure, leading to light-headedness or dizziness when standing up, so it helps to rise slowly. Over time, as Parkinson's progresses and treatment continues, people may develop involuntary movements or notice the medicine wearing off between doses, and the specialist team adjusts the timing and dose to manage this. It is important not to stop the combination suddenly, as this can cause a serious worsening of symptoms. Taking doses at regular, consistent times helps keep symptoms steady.
Who should not take it / use with caution
- People who have had a serious allergic reaction to carbidopa or levodopa should not take it.
- It is used with caution in people with certain heart, eye (closed-angle glaucoma) or mental-health conditions, under specialist guidance.
- It should not be used close to certain older antidepressants known as MAOIs, and any changes should be made under specialist supervision.
Monitoring
- Reviewing how well Parkinson's symptoms are controlled and adjusting timing and dose over time.
- Watching for blood-pressure drops, involuntary movements and wearing-off effects.
- Checking for changes in mood, sleepiness or impulsive behaviour.
Side effects
- Nausea, especially when treatment is first started.
- Light-headedness or dizziness on standing, from a drop in blood pressure.
- Over time, involuntary movements, vivid dreams, and occasionally sudden sleepiness or changes in mood or impulsive behaviour, which should be reported.
Key interactions
- It must not be combined with certain older antidepressants called MAOIs, which can cause a dangerous rise in blood pressure.
- Iron supplements and some antacids can reduce how well the levodopa it is paired with is absorbed, so separate the timing.
- A few medicines, including some used for nausea and certain antipsychotics, can work against its effect on Parkinson's.
Available as: Tablets taken by mouth, almost always combined with levodopa.
Answers
Carbidopa: frequently asked questions
What does carbidopa do?
It is given with levodopa in Parkinson's disease and stops levodopa being broken down before it reaches the brain, so more of it gets to where it is needed.
Does carbidopa work on its own?
No. On its own it has little effect on Parkinson's symptoms; its job is to help levodopa work better, which is why it is given as a combination product.
Why do I feel dizzy when I stand up?
The combination can lower blood pressure, causing light-headedness on standing, so it helps to get up slowly from sitting or lying down.
Why does it reduce nausea from levodopa?
By blocking the breakdown of levodopa outside the brain, carbidopa reduces the dopamine made in the body that causes nausea, so the combination is better tolerated.
Can I stop taking it suddenly?
No. Stopping the combination suddenly can cause a serious worsening of symptoms, so any changes should be made gradually under your specialist's guidance.
The wider class
About Levodopa-protecting medicine (Parkinson's)
Carbidopa belongs to the levodopa-protecting medicine (parkinson's) class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
Browse by body system
Authoritative sources
- BNF
- NICE CKS
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