Carbidopa and Levodopa (Oral)

Carbidopa and levodopa is a combination medication which is used to counteract some of the symptoms exhibited by Parkinson’s Disease patients, by supplying needed dopamine to the brain, where a dopamine deficiency has usually occurred.


It is thought by scientists that many patients who suffer from Parkinson’s Disease are experiencing a deficiency of a substance called dopamine in the brain, and that treatment of the disease should therefore focus on supplying that needed dopamine to the brain. This, in effect, is how carbidopa and levodopa work, as levodopa is changed into dopamine when it moves into the brain, thereby helping to control the erratic movements normally associated with Parkinson’s.

Levodopa’s partner medication, carbidopa, helps to prevent levodopa from being broken down by the body before it can reach the brain and become useful in symptom management. There is an additional benefit realized by pairing these two medications, in that carbidopa helps to mitigate some of the side effects which sometimes bother patients being treated, for instance, the nausea and vomiting which are fairly common.

While levodopa undergoes its conversion to dopamine as it crosses the so-called ‘blood-brain barrier’, carbidopa does not cross this barrier, and contributes by reducing side effects and lowering the dosage needed in order for levodopa to be effective.

As most people know, Parkinson's disease is a progressive neurodegenerative disorder which affects mobility and control of the muscular system. The disease is characterized by tremors, uncontrolled kinetic movements, and periodic rigidity. While the disease cannot be cured, the symptoms of the disease can be mitigated to some extent by treatments such as levodopa therapy.

Scientific research has demonstrated that many of the symptoms of Parkinson's disease are attributable to the fact that there is a depletion of dopamine in the corpus striatum. A straightforward administration of dopamine to a patient having Parkinson's disease would not be effective because dopamine by itself is unable to cross the blood-brain barrier.

However, that is not the case with levodopa, which is a metabolic precursor of dopamine that does have the capability of crossing the blood-brain barrier, after which it is converted into dopamine. There is a catch to this though because when levodopa is orally administered, it becomes rapidly decarboxylated before it has a chance to cross the blood-brain barrier and to become useful in treating the symptoms of the disease.

That makes it necessary to provide large doses of levodopa to a patient in order to achieve any kind of effective therapeutic response so that a significant amount actually crosses the blood-brain barrier where it can achieve a beneficial effect.

When levodopa is paired with carbidopa, the decarboxylation of levodopa is slowed significantly, making much more levodopa available to the brain for symptom relief. There are some drawbacks to this combination medication approach though, because patients being treated with carbidopa/levodopa sometimes develop noticeable motor fluctuations that have the appearance of on/off mobility function. This means that a patient's mobility may fluctuate between complete immobility and relatively complete mobility. In many cases, patients have also reported various levels of nausea and vomiting, which is likely attributable to the high dosage of levodopa necessary to achieve a therapeutic effect.

Condition Treated

  • Parkinson’s Disease

Type of Medicine

  • Inhibitor of aromatic amino acid decarboxylation

Side Effects

There are a number of side effects which may occur when taking carbidopa and levodopa in combination, some of which are relatively mild in nature and are not cause for alarm, while others are more serious and should be reported to your doctor. Some even call for immediate medical attention, to prevent the worsening of a major medical condition. The potential side effects from using the combination drug are listed below, categorized by level of severity. There are many people who used carbidopa/levodopa without incurring any side effects at all, or for just a few days, during the period when your body is becoming acclimated to using the drug.

The side effects in the milder category include the following:

• Anxiety or nervousness
• stools which may be tarry and black
• bluish tinge to the skin
• blurry vision
• tightening or discomfort in the area of the chest
• fevers and or chills
• convulsions or seizure-like symptoms
• coughing, raspiness or hoarseness in the throat
• light-headedness or dizziness, especially when rising up from a resting position
• dry mouth
• stubborn adherence to obviously false beliefs
• fast, irregular, pounding, or racing heartbeat or pulse
• thoughts about self-abuse or about hurting others
• general fatigue or weakness
• hyperventilation
• increased sex drive
• profuse sweating
• noticeable swelling in the areas of the face, eyes, lips, throat, or tongue
• unusual swelling of the legs, feet, hands, or sex organs
• sudden loss of bladder control
• unexplained pains in the lower back or sides
• nausea and or vomiting
• restlessness or inability to relax
• sensing things through sight or hearing which aren’t really there
• severe stiffness of the muscles
• shaking, trembling, jittery motions
• a persistent sore throat
• white spots or other sores which appear in the mouth or on the lips
• noticeable swelling of glands, especially in the throat
• tenderness on certain areas of the body
• unexplained bruising or bleeding
• paleness of the skin which is abnormal for a person

The following are some side effects which occur when taking carbidopa/levodopa which are considered to be more serious, and are manifestations which you should seek medical attention for:

• unusual facial expressions
• twisting motions of the arms, legs, neck, or trunk which cannot be controlled
• difficulty sleeping
• more frequent urination
• blinking of the eyelids or spasms in the muscles around the eyes
• pain in the bladder area
• urine which is cloudy or bloody
• unexplained chest pains
• confusion or disorientation
• trouble with speaking, breathing, or swallowing
• difficulty focusing or concentrating
• uncontrollable sticking out of the tongue
• general loss of interest or pleasure in daily life
• severe loss of appetite
• unusual irritability
• strong lower back pains
• feelings of sadness or emptiness
• burning sensation during urination
• inability to move the muscles of the eyes
• feeling, hearing, or seeing things when there's nothing there.

The side effects listed below are not considered to be cause for medical concern, and for most patients will generally fade away by themselves:

• temporary weight loss
• unusual dreams
• sensation of acid or sour stomach, often accompanied by discomfort or pain
• muscle cramps
• headaches
• various aches around the body
• unusual urge to belch
• feelings of numbness, itching, or tingling of the skin (the pins and needles feeling)
• persistent diarrhea
• difficulty with bowel movements
• heartburn or indigestion
• sneezing, runny nose, or nasal congestion
• congestion in the ears
• losing your voice
• unpleasant aftertaste in the mouth
• changes in taste
• blurriness or double vision
• persistent sensation of body warmth
• enlarged pupils
• dark-colored sweat
• temporary hair loss.

There are some other generalized side effects which should be noted when taking the carbidopa/levodopa combination drug. Patients have reported falling asleep suddenly after taking the drug, in the middle of their typical daily routine, and some of these instances occurred with no prior feeling of fatigue or tiredness.

This can be a dangerous situation if you happen to be driving or operating heavy machinery, because a sudden loss of consciousness could prove fatal. This situation has affected both new patients using the drug, and those who have been taking it for a long time with no prior side effects. If you do experience a sudden urge to rest or a powerful drowsiness, make sure to avoid any kinds of activities which would be hazardous to your health if you were to lose consciousness. The risk of this sudden sleepiness increases for those using alcohol at the time, or for those using other medications in tandem with carbidopa/levodopa.

You should contact your doctor immediately if you experience some of the more serious side effects mentioned above, like spasms which are uncontrollable or those which affect the eyes, like blurred vision, double vision, inability to move the eyes, etc.

If you should begin having hallucinations or extremely strange dreams while using this medication, you should consult with your doctor. It's also possible that you could begin to feel depression-like symptoms or thoughts of suicide while taking this drug, and that should likewise be discussed with your doctor.

A temporary sore throat is not really cause for alarm, but one that persists for days or weeks should definitely be reported to your physician. Chest pains are another thing that should not be dismissed, because they could be indicators of heart problems.

If you should abruptly terminate usage of this drug, there's a potential for a condition called neuroleptic malignant syndrome to be triggered, which can be very dangerous. Symptoms for this medical condition are a fast or irregular heartbeat, extremely rapid breathing, profuse sweating, severe disorientation or confusion, unusual stiffness of the muscles, and fevers, chills, or both.

It is rare for anyone to have a serious allergic reaction to carbidopa/levodopa, but you should seek emergency medical attention if you should experience swelling of the eyes, lips, tongue, or throat immediately after taking the drug.


Dosages prescribed for individual patients will generally be different and will depend on a number of factors. The amount of medicine which is prescribed for a given patient will depend on the strength of the medication as well as how frequently it is taken during the course of the day. The dosages listed below are considered to be standard dosages for different age groups and are not meant to be taken as the correct dosage for any specific individual.

Adults taking extended-release capsules – an initial dosage of carbidopa/levodopa should be one capsule taken three times daily over the course of the first three days. If your doctor notices undesirable side effects or an intolerance on your part, these dosages can be adjusted. No more than 10 capsules ingested in a single day should be recommended. A maintenance program of carbidopa/levodopa generally includes ingestion of three to four capsules daily, with a maximum of 10 capsules, as needed by the patient.

Children taking extended-release capsules – since reactions in children can be more pronounced than in adults, and since a lesser amount of medication is generally needed by children, there is no standard dosage recommended. Any children on a program of treatment with carbidopa/levodopa will have dosages worked out by close monitoring with the family physician.

Adults taking disintegrating tablets – an initial dosage is a single tablet taken three or four times during the course of a day as needed, up to a maximum of eight tablets in a single day. A maintenance program of medication is a single tablet taken 3 to 4 times daily, with a maximum of eight tablets to be ingested in a single day. Your doctor will make any necessary adjustments to the dosage, depending on your tolerance to the medication and to the results achieved.

Children taking disintegrating tablets – children will generally require a lesser amount of medication to achieve results, but there is no standardized dosage for children because of their wide range of tolerance. For this reason, a beneficial dosage will be worked out by the family doctor after closely monitoring results achieved and patient tolerance.

If you have missed a regularly scheduled dosage of carbidopa/levodopa, it is generally safe to take the missed dosage as soon as you think of it. However, if you don't think of it until a time which is very close to the next regularly scheduled dosage, you should skip the missed dosage entirely.

It is never advisable to double up on dosages because an excessive amount of the medication can overwhelm systems in the body. If you suspect that you have overdosed on carbidopa/levodopa, contact your doctor immediately and let him know exactly how much of the medication you have taken, as well as any symptoms you are experiencing. It may be necessary for you to seek emergency medical treatment in a situation like this.


There are some drugs which have known interactions with carbidopa/levodopa, and if you are taking any of these drugs, you should make certain to discuss it with your doctor. It is not recommended that any of the drugs listed below be used concurrently with carbidopa/levodopa, and if you are taking any of the drugs on this list, it is likely that your doctor will prescribe something other than carbidopa/levodopa to treat your medical condition.

• Phenelzine
• Sulpiride
• Tranylcypromine
• Toloxatone
• Procarbazine
• Amisulpride
• Bromopride
• Methylene blue
• Pargyline
• Moclobemide
• Nialamide
• Isocarboxazid
• Furazolidone
• Clorgyline
• Linezolid
• Iproniazid

It is not advisable to use carbidopa/levodopa in conjunction with either bupropion or isoniazid, but in certain situations, concurrent usage may be necessary to achieve desired results. In those cases, your doctor may recommend prescribe dosages which are non-standard, but which will avoid undesired side effects.

Another class of interactions includes those which occur with medications that can enhance or deepen certain side effects which a patient might be experiencing. If you are taking any of the drugs on this list, you should review with your doctor any side effects that you have, and how severe any of those side effects are. This will enable your doctor to make a determination about the advisability of using the drugs on this list. It may be necessary to alter the normal dosages of other drugs or of carbidopa/levodopa, if it is felt that necessary to take these drugs concurrently with carbidopa/levodopa.

• Tyrosine
• Spiramycin
• Droxidopa
• Metoclopramide
• Phenylalanine
• Phenytoin
• Kava
• Iron
• Indinavir
• Fosphenytoin.

There are some medications which should not be used in conjunction with carbidopa/levodopa around mealtimes, or when using alcohol or tobacco, since any of these can cause interactions to occur. The foods which may trigger a reaction when used in tandem with carbidopa/levodopa are those in the category of high protein foods, such as fish, meats, and dairy products.

It is possible for an interaction to occur when taking carbidopa/levodopa if you have an existing medical condition, and the conditions on this list should always be discussed with the family doctor before taking the drug for that reason.

• Asthma
• depression or other mental disorders
• dyskinesia
• endocrine disease
• any kinds of problems with heart rhythm, such as ventricular tachycardia
• any history of heart attacks or stroke
• any known problems with blood vessels or heart disease
• kidney disease
• liver disease
• skin lesions or any undiagnosed rashes
• phenylketonuria
• melanoma or suspicion of melanoma
• narrow angle glaucoma
• lung disease or respiratory disease
• peptic ulcers
• psychosis.


Make sure to tell your doctor if you know you are allergic to either carbidopa or levodopa, or any of the ingredients included in them. You should also let your doctor know if you are aware of any other allergies at all which you have, because these could possibly be triggered by the medication. There are some inactive ingredients in the two medications which may cause allergic reactions when combined with other ingredients.

Before agreeing to a program of treatment which includes carbidopa/levodopa, you should have a thorough discussion with your family doctor about your medical history, especially as it relates to all of the following conditions:

• liver disease
• breathing problems such as asthma
• mental or mood disorders such as schizophrenia or severe depression
• blood disorders
• convulsions or seizures
• glaucoma
• any kind of heart disease or irregular heartbeat
• kidney disease
• stomach or intestinal disorders
• any kind of sleeping disorders or difficulties.

You should be aware of the potential for this drug to cause drowsiness during your waking hours, sometimes without any prior indications of impending sleepiness. Since there is a potential for you to suddenly fall asleep, it is advisable to avoid operating a motor vehicle or any kind of dangerous machinery while you are taking carbidopa/levodopa. For the same reason, you should avoid using alcohol while taking this drug, and you should also avoid any kinds of medication which may induce drowsiness, because the effects can be multiplied.

It is highly advisable that you prepare a comprehensive list of all other prescription drugs you are taking, as well as any over-the-counter drugs, vitamins, and dietary supplements, as well as all the dosages for each of these. Your doctor will need to review this list so that a determination can be made about any potential interactions between drugs, as well as to develop a plan for dosage which does not conflict with other medications you may be taking.

It will be a good idea to have this list ready if you ever have to make an unscheduled trip to an emergency room or a health clinic, because doctors there will not be aware of your medical history or your roster of current medications. Having all this information readily available will allow a doctor at the clinic to treat your condition safely without conflicting with any of your other medications.

Women who are currently pregnant or plan to become pregnant, should discuss the situation with a family doctor, because there is a potential for carbidopa/levodopa to impact the fetus at some point. It is known that levodopa does pass into breast milk, but it is unclear whether or not carbidopa passes into breast milk, so it is not advisable for pregnant women to be breast-feeding while on this medication. Since the levodopa portion of the drug can be passed on to an infant, there is at least the potential for a large amount of dopamine to be ingested by an infant, the impact of which has not been extensively studied.


Your carbidopa/levodopa medication should be stored in a location well away from the reach of children and pets, because accidental ingestion could prove to be very dangerous. The medication should also not be kept in a pill reminder container, because these are seldom equipped with safety locks which prevent tampering and/or unwanted access.

Your medication should not be frozen, or kept in a room which is subject to direct sunlight, high heat, or excessive humidity, as all these conditions can degrade the effectiveness of the medication. Bathrooms are a poor place for storage because these kinds of conditions are common in such rooms, especially during times of bathing or showering.

Any portion of your medication which goes unused or which the expiration date has been exceeded, should be disposed of in a safe manner. If you are unsure about how to dispose of unused carbidopa/levodopa, consult your physician or your pharmacist for advice on how to proceed.


Carbidopa and levodopa are often used in tandem, because the beneficial effects of treating symptoms of Parkinson’s disease are best achieved when these drugs work together. Without carbidopa, the levodopa would break down in the body much more quickly, and its effectiveness would be quite limited. It is the levodopa which becomes decarboxylated in the body and is transformed into dopamine, which is the substance that mitigates the tremors and shakiness commonly associated with Parkinson’s.

Carbidopa also has the effect of reducing some of the potential side effects which a patient might experience, for instance the sensation of nausea, and of vomiting. Without carbidopa to lessen these side effects, anyone taking levodopa alone would probably experience much more pronounced side effects and discomfort.

While there are a number of potential side effects associated with taking carbidopa and levodopa, it is uncommon for them to be severe, and for many people, there are no side effects experienced at all. While on a program of treatment with carbidopa and levodopa, there are some other medications and some other medical conditions which can be affected, so all these must be reviewed with a family doctor.