Do not take carbidopa and levodopa if you have used an MAO inhibitor such as isocarboxazid (Marplan), phenelzine (Nardil), or tranylcypromine (Parnate) within the past 14 days. Serious, life-threatening side effects can occur if you take carbidopa and levodopa before the MAO inhibitor has cleared from your body. 

You should not take this medication if you are allergic to carbidopa (Lodosyn) or levodopa (Larodopa), or if you have:

narrow-angle glaucoma;

unusual skin lesions that have not been checked by a doctor; or

a history of malignant melanoma (skin cancer).

If you have any of these other conditions, you may need a dose adjustment or special tests:

heart disease, high blood pressure, coronary artery disease, a heart rhythm disorder, or a prior heart attack;

asthma, chronic obstructive pulmonary disease (COPD), or other breathing disorder;
liver or kidney disease;

an endocrine (hormonal) disease;

a stomach or intestinal ulcer;

wide-angle glaucoma; or

depression or other mental illness.
Carbidopa and levodopa may cause you to fall asleep during normal daytime activities such as working, talking, eating, or driving. You may fall asleep suddenly, even after feeling alert. Tell your doctor if you have any problems with daytime sleepiness or drowsiness.

You may have increased sexual urges, unusual urges to gamble, or other intense urges while taking carbidopa and levodopa. It is not known whether the medicine actually causes this effect. Talk with your doctor if you believe you have any intense or unusual urges while taking carbidopa and levodopa.

Some people taking medicines for Parkinson's disease have developed skin cancer (melanoma). However, people with Parkinson's disease may have a higher risk than most people for developing melanoma. Talk to your doctor about your specific risk and what skin symptoms to watch for. You may need to have regular skin exams.
FDA pregnancy category C. It is not known whether carbidopa and levodopa will harm an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant while using this medication. Carbidopa and levodopa may pass into breast milk and could harm a nursing baby. Do not use this medication without telling your doctor if you are breast-feeding a baby.

The disintegrating tablet (such as Parcopa) may contain phenylalanine. Talk to your doctor before using this form of carbidopa and levodopa if you have phenylketonuria (PKU).

If you missed the dose take it as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.

You may notice that your sweat, urine, or saliva appears dark in color, such as red, brown, or black. This is not a harmful side effect, but it may cause staining of your clothes or bed sheets.
Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat. Call your doctor at once if you have any of these serious side effects:

restless muscle movements in your eyes, tongue, jaw, or neck;

worsening of tremors (uncontrolled shaking);

high fever, stiff muscles, sweating, fast or uneven heartbeats, rapid breathing, feeling like you might pass out;

seizure (convulsions);

painful or difficult urination;

severe nausea, vomiting, or diarrhea;

uneven heart rate or fluttering in your chest;

confusion, hallucinations, anxiety, agitation, depressed mood, thoughts of suicide or hurting yourself;

chest pain or heavy feeling, pain spreading to the arm or shoulder.

Less serious side effects may include:

mild nausea, dry mouth, loss of appetite, heartburn, diarrhea, constipation;

headache, dizziness, drowsiness, blurred vision;

sneezing, stuffy nose, cough, or other cold symptoms;

sleep problems (insomnia), strange dreams;

muscle pain, numbness or tingly feeling; or

skin rash or itching.

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