Does Carbidopa (L-Dopa decarboxylase inhibitor) cause diarrhea?

From the Guidelines

Carbidopa can cause diarrhea as a side effect in some patients, particularly when used in combination with levodopa for Parkinson's disease treatment. According to the espen guideline clinical nutrition in neurology study 1, several side-effects related to drugs prescribed for PD, including diarrhea, have been mentioned by patients to attribute to their weight loss, as well as changes in taste and smell of food. The study highlights that the use of levodopa, often in combination with carbidopa, may be associated with impaired nutritional status and risk for malnutrition.

If you're experiencing carbidopa-induced diarrhea, don't abruptly stop your medication, but consult your healthcare provider who may adjust your dosage or recommend taking the medication with food to reduce gastrointestinal irritation. Over-the-counter antidiarrheal medications like loperamide (Imodium) at standard doses (initially 4mg followed by 2mg after each loose stool, not exceeding 16mg daily) may provide temporary relief, as suggested by general medical practice. Staying hydrated and following a BRAT diet (bananas, rice, applesauce, toast) can help manage symptoms.

Key points to consider:

• Carbidopa affects gut motility through dopaminergic pathways in the enteric nervous system, which may lead to diarrhea.
• Adjusting the dosage or taking the medication with food may help reduce gastrointestinal irritation.
• Alternative formulations or adding medications like domperidone may be considered to counteract the gastrointestinal side effects while maintaining the therapeutic benefits for Parkinson's disease.
• Regular monitoring of body weight and nutritional assessment is recommended for PD patients, as weight loss and malnutrition can be associated with disease severity and progression 1.

From the FDA Drug Label

Gastrointestinal Dark saliva, gastrointestinal bleeding, development of duodenal ulcer, anorexia, vomiting, diarrhea, constipation, dyspepsia, dry mouth, taste alterations

• Diarrhea is listed as a potential adverse reaction of carbidopa and levodopa tablets.
• The FDA drug label for carbidopa 2 directly supports that diarrhea is a possible side effect.
• Therefore, yes, Carbidopa (L-Dopa decarboxylase inhibitor) can cause diarrhea.

From the Research

Carbidopa and Diarrhea

• Carbidopa is a L-Dopa decarboxylase inhibitor used in the treatment of Parkinson's disease.
• The association between Carbidopa and diarrhea is observed in several studies:
  • A 2024 study 3 reported that 21% of patients discontinued Levodopa-Entacapone-Carbidopa intestinal gel treatment due to side effects, mostly diarrhea.
  • Other studies 4, 5, 6, 7 do not specifically mention diarrhea as a common side effect of Carbidopa, but they do report various adverse events and complications associated with Levodopa-Carbidopa intestinal gel treatment.

Adverse Events and Complications

• The studies 4, 3, 5, 6, 7 report the following adverse events and complications:
  • Gastrointestinal complications, such as those related to the intestinal infusion system 5, 6
  • Device-related complications, such as jejunal tube replacement and percutaneous endoscopic gastrostomy tube replacement 5
  • Serious adverse events, including death 3
  • Minor complications, such as those reported in the 2022 study 4

Treatment Outcomes

• The studies 4, 3, 5, 6, 7 report the following treatment outcomes:
  • Improved motor function and reduced "off" time 5, 6, 7
  • Increased "on" time without dyskinesia 5, 6
  • Improved quality of life 5, 6, 7
  • Reduced polypharmacy for patients with advanced Parkinson's disease 7