What Is Carbidopa/Levodopa Therapy?

The combination of levodopa and carbidopa is a treatment used for Parkinson’s disease (PD). Levodopa/carbidopa is the most effective treatment available for the motor symptoms of PD. Levodopa was first discovered as a treatment for the symptoms of Parkinson’s disease more than 50 years ago.1-4

How does it work?

Dopamine is a neurotransmitter (chemical messenger) with many jobs. Dopamine is responsible for producing smooth, purposeful movement. PD damages the neurons in the brain that make dopamine. This causes the motor symptoms of PD. This includes symptoms like:1-4

  • Tremor
  • Rigidity
  • Impaired balance
  • Loss of spontaneous movement

These motor symptoms are related to the loss of dopamine in the brain. By the time motor symptoms of PD appear, about 60 to 80 percent of the neurons in the brain that make dopamine have already been damaged or destroyed.1-4

Dopamine cannot enter our brains. This means that dopamine by itself cannot work as a treatment for PD. However, levodopa can enter the brain. Levodopa is the building block our bodies can use to make dopamine. Levodopa is converted to dopamine in the brain. The influx of dopamine created by levodopa helps treat the motor symptoms of PD.1-4

Adding carbidopa prevents levodopa from being converted into dopamine in the bloodstream. This allows more of the drug to get to the brain. This also means that lower doses of levodopa can be given. The addition of carbidopa also reduces the risk of some side effects like nausea or vomiting.1,2

Examples of different therapies

Several different carbidopa/levodopa therapies are used to treat PD, including:1

  • Sinemet® (carbidopa levodopa)
  • Sinemet® CR (carbidopa levodopa ER)
  • Parcopa® (carbidopa levodopa) orally disintegrating tablet
  • Stalevo® (carbidopa/levodopa/entacapone)
  • Rytary® (carbidopa levodopa ER)
  • Inbrija® (levodopa inhalation powder)
  • Duopa® (carbidopa levodopa) enteral suspension

There are different dosages for each of these therapies. People may be prescribed different dosages at different points in their disease to manage their symptoms.1

  • Sinemet® – A tablet that comes in 3 different strengths.
  • Sinemet® CR – A sustained-release tablet that releases the ingredients over a longer timeframe. Sinemet CR is no longer produced, but some generic forms are.
  • Parcopa® – Taken by mouth and dissolves on the tongue. No water is required to take Parcopa.
  • Stalevo® – A tablet that includes carbidopa, levodopa, and entacapone. Entacapone may allow more levodopa to reach the brain. It blocks the COMT enzyme that breaks down levodopa and dopamine.
  • Rytary® – An extended-release tablet that comes in 4 different strengths.
  • Inbrija® – A form of levodopa that is inhaled when someone has an "off" period.
  • Duopa® – A gel that is delivered directly into the intestines by a pump for up to 16 hours. It requires a procedure to make a small hole (stoma) in the stomach wall. It is an option for people who still have PD symptoms with oral treatments.

What are the possible side effects?

The most common side effects of carbidopa/levodopa therapy include:1

  • Nausea
  • Vomiting
  • Falling blood pressure that occurs upon standing (orthostatic hypotension)
  • Worsening of glaucoma (a condition that damages the eye)
  • Dyskinesia (spontaneous, involuntary movements)
  • Hallucination (seeing things that are not real)
  • Psychosis
  • Low blood pressure
  • Confusion
  • Dry mouth
  • Dizziness

Dyskinesias are a common side effect of long-term levodopa therapy. Dyskinesias can impact quality of life. The severity of dyskinesia due to levodopa varies among people with PD. The risk of dyskinesia is higher in early-onset PD. Medicines may be added or adjusted to prevent dyskinesia. Deep brain stimulation may also be an option.3,5

These are not all the possible side effects of carbidopa/levodopa therapy. Talk to your doctor about what to expect when taking carbidopa/levodopa therapy. You should also call your doctor if you have any changes that concern you when taking carbidopa/levodopa therapy.

Additional therapy

For some people, their PD symptoms are not well controlled by carbidopa/levodopa. In this case, more treatments may be added. People may also be switched to other drugs. Other treatments for PD symptoms include:4

  • Dopamine agonists
  • Monoamine oxidase-B (MAO-B) inhibitors
  • Surgery for deep brain stimulation

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Written by: Emily Downward and Juliette Daly | Last reviewed: September 2021