Can a person take levothyroxine and Levodopa (L-Dopa) simultaneously?

From the Guidelines

It is recommended to take levothyroxine and levodopa at least 4 hours apart to minimize potential interactions, with levothyroxine typically taken in the morning on an empty stomach and levodopa taken with food to reduce stomach upset. When considering the concomitant use of these medications, it's essential to prioritize the patient's medical history and potential risk factors for drug interactions, such as liver function 1. Although the provided study does not directly address the interaction between levothyroxine and levodopa, it highlights the importance of understanding the mechanism behind drug-drug interactions and monitoring patients for potential toxicity or efficacy changes 1. Some key points to consider when taking these medications together include:

• Levothyroxine absorption can be decreased when taken with certain medications or foods, emphasizing the need for a separation in dosing times.
• Levodopa is usually taken with food to reduce stomach upset, which may affect its timing relative to levothyroxine intake.
• Both medications play critical roles in managing the patient's condition - levothyroxine for thyroid hormone replacement and levodopa for Parkinson's disease symptom management.
• Regular monitoring and open communication with the healthcare provider are crucial to adjust the medication schedule as needed and prevent potential interactions. Given the lack of direct evidence on the interaction between levothyroxine and levodopa in the provided study, the recommendation is based on general principles of drug administration and the importance of minimizing potential interactions to ensure the patient's safety and the efficacy of both medications 1.

From the Research

Interaction between Levothyroxine and Levodopa

• There is no direct evidence in the provided studies that discusses the interaction between levothyroxine and levodopa.
• However, a study from 1981 2 found that 3 out of 46 patients with Parkinson's disease were hypothyroid, suggesting that thyroid function should be evaluated in patients with Parkinson's disease.
• The same study found that the duration or quantity of L-dopa or carbidopa/L-dopa therapy did not influence thyroid function assessments.
• Other studies 3, 4, 5, 6 discuss the treatment of Parkinson's disease with levodopa, but do not mention the interaction with levothyroxine.

Pharmacokinetics of Levodopa

• A study from 2024 5 discusses the clinical pharmacokinetics of levodopa and relevant add-on therapies for Parkinson's disease.
• The study found that the addition of catechol-O-methyltransferase inhibitors, such as opicapone, can increase the plasma appearance of levodopa and reduce 3-O-methyldopa synthesis.
• Another study from 2017 6 reviews the population pharmacokinetics/pharmacodynamics analysis of levodopa in Parkinson's disease.
• The study found that the optimal dosage of levodopa is complicated by marked between-subject and between-occasion variability in this population.

Treatment of Parkinson's Disease

• A study from 2020 3 discusses the diagnosis and treatment of Parkinson's disease, including the use of levodopa preparations.
• The study found that treatment involves pharmacologic approaches, such as levodopa preparations, and nonpharmacologic approaches, such as exercise and physical therapy.
• Another study from 2020 4 reviews the approved and emerging therapies for improving the delivery of levodopa in Parkinson's disease.
• The study found that novel technologies and delivery devices are being developed to provide a more consistent and sustained levodopa delivery.