Reviewed on 9/13/2021

What Is Carbidopa and How Does It Work?

Carbidopa is a prescription drug used in treatment of Parkinson's disease, postencephalitic parkinsonism, and symptomatic parkinsonism.

Carbidopa is available under the following different brand names: Lodosyn.

Dosages of Carbidopa

Adult and Pediatric Dosages:


  • 25 mg

Dosage Considerations – Should be Given as Follows:

Parkinson's Disease

  • For use with carbidopa-levodopa or with levodopa for Parkinson's disease in patients for whom the dosage of carbidopa-levodopa combo provides less than adequate daily dosage of carbidopa, or in patients whose dosage requirement of carbidopa and levodopa necessitates separate titration of each entity
  • Dosage dependent upon concurrent dose of carbidopa-levodopa or levodopa and and patient's specific needs
  • Patients taking Sinemet 10/100: Administer 25 mg carbidopa daily with first daily dose of Sinemet 10/100 if necessary; may administer 12.5-25 mg carbidopa with each subsequent dose of Sinemet 10/100; not to exceed 200 mg carbidopa/day including carbidopa from Sinemet
  • Patients taking Sinemet 25/250 or 25/100: Administer 25 mg carbidopa daily with either Sinemet strength throughout the day; not to exceed 200 mg/day of carbidopa including the Sinemet combination
  • Titration of carbidopa and levodopa (individually)
  • Administer 25 mg carbidopa orally every 6-8 hours concurrently with levodopa; administer 20-25% less than the previous levodopa in carbidopa naive patients; first dose of carbidopa should be taken before or at 12 hours after the test dose of levodopa in carbidopa naive patients; increase or decrease dose by 1/2 or 1 tablet/day


  • Safety and efficacy not established


Dementia, Alzheimer's Disease, and Aging Brains See Slideshow

What Are Side Effects Associated with Using Carbidopa?

Common side effects of carbidopa include:

  • agitation
  • allergic reaction (difficulty breathing, closing of the throat, swelling of the lips, tongue, or face or hives)
  • anxiety
  • blurred vision
  • confusion
  • constipation
  • darkening or urine or sweat
  • decreased appetite
  • depression or suicidal thoughts
  • dizziness or drowsiness
  • dry mouth
  • fatigue
  • hand tremor
  • insomnia
  • irregular heart beat or fluttering in your chest
  • mild nausea
  • muscle twitches
  • nightmares
  • persistent nausea, vomiting, or diarrhea
  • seizures
  • uncontrolled movements of a part of the body
  • unusual changes in mood or behavior
  • vomiting

This document does not contain all possible side effects and others may occur. Check with your physician for additional information about side effects.

What Other Drugs Interact with Carbidopa?

If your doctor has directed you to use this medication, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider or pharmacist first.

  • Carbidopa has no known severe interactions with other drugs.
  • Carbidopa has no known serious interactions with other drugs.
  • Carbidopa has moderate interactions with 71 different drugs.
  • Minor interactions of carbidopa include:

This information does not contain all possible interactions or adverse effects. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share this information with your doctor and pharmacist. Check with your health care professional or doctor for additional medical advice, or if you have health questions, concerns or for more information about this medicine.

What Are Warnings and Precautions for Carbidopa?


This medication contains carbidopa. Do not take Lodosyn if you are allergic to carbidopa or any ingredients contained in this drug.

Keep out of reach of children. In case of overdose, get medical help or contact a Poison Control Center immediately.


  • Hypersensitivity
  • Nonselective monoamine oxidase (MAO) inhibitors are contraindicated for use with levodopa or carbidopa-levodopa combination products with or without carbidopa. These inhibitors must be discontinued at least two weeks prior to initiating therapy with carbidopa. Carbidopa-levodopa or levodopa may be administered concomitantly with the manufacturer's recommended dose of an MAO inhibitor with selectivity for MAO type B (selegiline HCl)
  • Carbidopa or carbidopa-levodopa products, with or without cardibopa, are contra-indicated in patients with narrow-angle glaucoma

Effects of Drug Abuse

  • None

Short-Term Effects

  • See "What Are Side Effects Associated with Using Carbidopa?"

Long-Term Effects

  • See "What Are Side Effects Associated with Using Carbidopa?"



  • As with carbidopa alone, periodic evaluations of hepatic, hematopoietic, cardiovascular, and renal function are recommended during extended concomitant therapy with carbidopa and levodopa, or with carbidopa and carbidopa-levodopa or any combination of these drugs

Impulse Control/Compulsive Behaviors

  • Postmarketing reports suggest that patients treated with anti-Parkinson medications can experience intense urges to gamble, increased sexual urges, intense urges to spend money uncontrollably, binge eating, and other intense urges. Patients may be unable to control these urges while taking one or more of the medications that are used for the treatment of Parkinson's disease and that increase central dopaminergic tone, including carbidopa taken with levodopa and lodosyn. In some cases, although not all, these urges were reported to have stopped when the dose of anti-Parkinson medications was reduced or discontinued. Because patients may not recognize these behaviors as abnormal it is important for prescribers to specifically ask patients or their caregivers about the development of new or increased gambling urges, sexual urges, uncontrolled spending or other urges while being treated with carbidopa. Physicians should consider dose reduction or stopping carbidopa or levodopa if a patient develops such urges while taking carbidopa with carbidopa/levodopa.

Hallucinations/Psychotic-Like Behavior

  • Hallucinations and psychotic like behavior have been reported with dopaminergic medications. In general, hallucinations present shortly after the initiation of therapy and may be responsive to dose reduction in levodopa. Hallucinations may be accompanied by confusion and to a lesser extent sleep disorder (insomnia) and excessive dreaming. Carbidopa when taken with carbidopa-levodopa may have similar effects on thinking and behavior. This abnormal thinking and behavior may present with one or more symptoms, including paranoid ideation, delusions, hallucinations, confusion, psychotic-like behavior, disorientation, aggressive behavior, agitation, and delirium.
  • Ordinarily, patients with a major psychotic disorder should not be treated with carbidopa and carbidopa-levodopa, because of the risk of exacerbating psychosis. In addition, certain medications used to treat psychosis may exacerbate the symptoms of Parkinson's disease and may decrease the effectiveness of carbidopa.


  • Carbidopa may potentiate the dopaminergic side effects of carbidopa and may cause or exacerbate preexisting dyskinesia.


  • Patients treated with carbidopa and carbidopa-levodopa should be observed carefully for the development of depression with concomitant suicidal tendencies.


  • Epidemiological studies have shown that patients with Parkinson's disease have a higher risk (2 to approximately 6-fold higher) of developing melanoma than the general population. Whether the observed increased risk was due to Parkinson's disease or other factors, such as drugs used to treat Parkinson's disease, is unclear
  • For the reasons stated above, patients and providers are advised to monitor for melanomas frequently and on a regular basis when using carbidopa tablets for Parkinson's disease
  • Ideally, periodic skin examinations should be performed by appropriately qualified dermatologists

Laboratory Tests

  • Abnormalities in laboratory tests may include elevations of liver function tests such as alkaline phosphatase, SGOT (AST), SGPT (ALT), lactic dehydrogenase, and bilirubin. Abnormalities in blood urea nitrogen and positive Coombs test have also been reported. Commonly, levels of blood urea nitrogen, creatinine, and uric acid are lower during concomitant administration of carbidopa and levodopa than with levodopa alone
  • Carbidopa and carbidopa-levodopa combination products may cause a false-positive reaction for urinary ketone bodies when a test tape is used for determination of ketonuria. This reaction will not be altered by boiling the urine specimen. False-negative tests may result with the use of glucose-oxidase methods of testing for glucosuria

Carcinogenesis, Mutagenesis, Impairment of Fertility


  • There were no significant differences between treated and control rats with respect to mortality or neoplasia in a 96-week study of carbidopa at oral doses of 25, 45, or 135 mg/kg/day. Combinations of carbidopa and levodopa (10-20, 10-50, 10-100 mg/kg/day) were given orally to rats for 106 weeks. No effect on mortality or incidence and type of neoplasia was seen when compared to concurrent controls.


  • Mutagenicity studies have not been performed with either carbidopa or the combination of carbidopa and levodopa.


  • Carbidopa had no effect on the mating performance, fertility, or survival of the young when administered orally to rats at doses of 30, 60, or 120 mg/kg/day. The highest dose caused a moderate decrease in body weight gain in males
  • The administration of carbidopa-levodopa at dose levels of 10-20, 10-50, or 10-100 mg/kg/day did not adversely affect the fertility of male or female rats, their reproductive performance, or the growth and survival of the young

Pregnancy and Lactation

  • There are no adequate and well-controlled studies with carbidopa in pregnant women. It has been reported from individual cases that carbidopa crosses the human placental barrier, enters the fetus, and is metabolized. Carbidopa concentrations in fetal tissue appeared to be minimal. Carbidopa should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus
  • Carbidopa, at doses as high as 120 mg/kg/day, was without teratogenic effects in the mouse or rabbit. In the rabbit, but not in the mouse, carbidopa-levodopa produced visceral anomalies, similar to those seen with levodopa alone, at approximately 7 times the maximum recommended human dose. The teratogenic effect of levodopa in rabbits was unchanged by the concomitant administration of carbidopa
  • It is not known whether carbidopa is excreted in human milk. Because many drugs are excreted in human milk, and because of their potential for serious adverse reactions in nursing infants, a decision should be made whether to discontinue breastfeeding or to discontinue the drug, taking into account the importance of the drug to the breastfeeding woman


Parkinson's disease is only seen in people of advanced age. See Answer
Medscape. Carbidopa.
RxList. Lodosyn Side Effects Drug Center.

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