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Carbidopa and levodopa

by Sama Mohamed · February 14, 2026

Drug Class: Dopaminergic antiparkinsonism agents

Active Ingredient: Carbidopa, Levodopa

Generic Name: Carbidopa/Levodopa

Brand Name: Sinemet® (and multiple international generics)

Company: Originally developed and marketed by Merck & Co.; currently manufactured by multiple international generic pharmaceutical companies

Dosage Form:

Tablet, orally disintegrating tablet, extended-release tablet, capsule

Drug Form: Capsule

Tablet Description: Chemical description: Levodopa (L-3,4-dihydroxyphenylalanine) has the molecular formula C₉H₁₁NO₄. Carbidopa has the molecular formula C₁₀H₁₄N₂O₄. Pharmacological description: Levodopa is a metabolic precursor of dopamine that crosses the blood–brain barrier and is converted to dopamine in the CNS. Carbidopa inhibits peripheral aromatic L-amino acid decarboxylase, reducing peripheral metabolism of levodopa and increasing its availability in the brain while decreasing peripheral side effects.

What is carbidopa and levodopa?

Carbidopa and levodopa may be used alone or in combination with other medication to treat symptoms of Parkinson’s disease, such as stiffness or tremors in adults.

Carbidopa and levodopa is also used in adults to treat Parkinson’s disease caused by infection, carbon monoxide poisoning or manganese intoxication.

Carbidopa and levodopa may also be used for purposes not listed in this medication guide.

Carbidopa and levodopa side effects

Get emergency medical help if you have signs of an allergic reaction: hives, difficult breathing, swelling of your face, lips, tongue, or throat.

Tell your doctor right away if you have new or sudden changes in mood or behavior, including depression or anxiety, panic attacks, trouble sleeping, or if you feel impulsive, irritable, agitated, aggressive, more active or talkative, or have thoughts about suicide or hurting yourself.

Some people taking carbidopa and levodopa have fallen asleep during normal daytime activities such as working or driving after starting carbidopa and levodopa and up to a year after. Tell your doctor if you have any problems with daytime sleepiness.

Carbidopa and levodopa may cause serious side effects. Call your doctor at once if you have:

  • signs of stomach bleeding–bloody or tarry stools, coughing up blood or vomit that looks like coffee grounds;
  • uncontrolled muscle movements, blurred vision, eye pain or redness, seeing halos around lights; or
  • severe nervous system reaction–very stiff (rigid) muscles, high fever, sweating, confusion, fast or uneven heartbeats, tremors, feeling like you might pass out.

You may have increased sexual urges, unusual urges to gamble, or other intense urges while taking this medicine. Talk with your doctor if this occurs.

Your dose may be reduced or permanently discontinued if you have certain side effects.

Common side effects of carbidopa and levodopa may include:

  • uncontrolled muscle movements;
  • dry mouth, anxiety, headache, dizziness;
  • drops in blood pressure or feeling light-headed when standing up;
  • sleep problems (insomnia), strange dreams, muscle contractions; or
  • nausea, vomiting, constipation.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects.

Warnings

Do not use this medicine if you have used a MAO inhibitor in the past 14 days, such as isocarboxazid, linezolidmethylene blue injection, phenelzine, or tranylcypromine.

Some people have thoughts about suicide while taking carbidopa and levodopa. Tell your doctor right away if you have any sudden changes in mood or behavior, or thoughts about suicide.

Before taking this medicine

You should not use carbidopa and levodopa if you are allergic to it or any of its ingredients, or if you have narrow-angle glaucoma.

Do not use carbidopa and levodopa if you have used a MAO inhibitor in the past 14 days. A dangerous drug interaction could occur. MAO inhibitors include isocarboxazid, linezolid, methylene blue injection, phenelzine, and tranylcypromine. Wait at least 14 days after stopping an MAO inhibitor before you take carbidopa and levodopa.

If you already take levodopa, you must stop taking it at least 12 hours before you start taking carbidopa and levodopa.

Tell your doctor if you have or have ever had:

  • an endocrine disease, heart disease, high blood pressure, or heart attack;
  • asthma, chronic obstructive pulmonary disease (COPD), or other breathing disorder;
  • skin cancer (melanoma), a stomach or intestinal ulcer;
  • glaucoma, depression, mental illness, or psychosis;
  • if you received general anesthesia; or
  • liver or kidney disease.

The orally disintegrating tablet may contain phenylalanine and could be harmful if you have phenylketonuria (PKU). Ask your doctor about your risk.

Some people have thoughts about suicide while taking carbidopa and levodopa. Stay alert to changes in your mood or symptoms. Your family or caregivers should also watch for sudden changes in your behavior.

People with Parkinson’s disease may have a higher risk of skin cancer (melanoma). Ask your doctor about skin symptoms to watch for.

It is not known if carbidopa and levodopa will harm an unborn baby. The benefit of this treatment may outweigh any risks to the mother and baby. Tell your doctor if you are pregnant or plan to become pregnant.

Ask a doctor if it is safe to breastfeed while using carbidopa and levodopa.

How should I take carbidopa and levodopa?

Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose. Use the medicine exactly as directed.

Stop taking any other medications that contain carbidopa and levodopa when you start taking the extended-release form.

Your dose needs may change if you switch to a different brand, strength, or form of this medicine. Avoid medication errors by using exactly as directed on the label, or as prescribed by your doctor.

Take this medicine at evenly spaced intervals. Follow your doctor’s instructions about whether to take your medication with food or on an empty stomach.

Swallow the capsule whole and do not crush, chew, break, or open it. The tablet is sometimes broken in half to give the correct dose. Always swallow a whole or half tablet without chewing or crushing.

If you cannot swallow an extended-release capsule whole, open it and mix the medicine with applesauce. Swallow the mixture right away without chewing.

Remove an orally disintegrating tablet from the package with dry hands only when you are ready to use the medicine. Allow the orally disintegrating tablet to dissolve in your mouth without chewing.

It may take up to several weeks before your symptoms improve. Tell your doctor if your symptoms do not improve or if the effects of this medicine wear off quickly between doses.

Carbidopa and levodopa will most likely darken the color of your saliva, urine, or sweat to an orange or red color. This is a normal effect and is not harmful. This may also cause stains to your underwear that may be permanent.

You may need frequent medical tests and your doctor will need to check your progress on a regular basis.

This medicine can affect the results of certain medical tests. Tell any doctor who treats you that you are using carbidopa and levodopa.

Do not stop using carbidopa and levodopa suddenly, or you could have unpleasant withdrawal symptoms (such as agitation, confusion, tingling). Ask your doctor before stopping the medicine.

You may need to follow a special diet. Learn about the foods you should eat or avoid.

Store tightly closed at room temperature, away from moisture, heat, and light.

What happens if I miss a dose?

Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

Get your prescription refilled before you run out of medicine completely.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line .

What should I avoid while taking carbidopa and levodopa?

Avoid driving or hazardous activity until you know how carbidopa and levodopa will affect you. Dizziness or drowsiness can cause falls, accidents, or severe injuries. Also avoid getting up too fast from a sitting or lying position, or you may feel dizzy.

Drinking alcohol with this medicine can cause side effects.

Avoid taking iron supplements, high-fat, or high-calorie meals before or after taking carbidopa and levodopa. These can make it harder for your body to absorb carbidopa and levodopa.

What other drugs will affect carbidopa and levodopa?

Using carbidopa and levodopa with other drugs that make you drowsy can worsen this effect. Ask your doctor before using opioid medication, a sleeping pill, a muscle relaxer, or medicine for anxiety or seizures.

When you start or stop taking carbidopa and levodopa, your doctor may need to adjust the doses of other medicines you use on a regular basis.

Tell your doctor about all your other medicines, especially:

  • phenytoin, metoclopramide;
  • papaverine, isoniazid, selegiline, reserpine, tetrabenazine;
  • vitamin or mineral supplements that contain iron; or
  • medicine to treat blood pressure, nausea or vomiting, anxiety, mood disorders, or mental illness such as schizophrenia.

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