Lisdexamfetamine and Levothyroxine Co-administration
Concomitant use of lisdexamfetamine (Vyvanse) and levothyroxine is not listed as an absolute contraindication. [1] A clinically relevant interaction is mainly pharmacodynamic, with sympathomimetic effects potentially increased when thyroid hormone is used at higher doses. [1]
Interaction Classification
The concomitant use is classified as a “Moderate” interaction on a drug-interaction database. [1] Sympathomimetic effects may be potentiated with thyroid hormones, especially with larger levothyroxine doses. [1]
Medication Timing for Levothyroxine Absorption
Levothyroxine is recommended to be taken once daily on an empty stomach, typically 30 to 60 minutes before breakfast, with water. [2] Levothyroxine absorption should be separated from drugs that decrease absorption, including agents such as iron and calcium supplements and antacids. [2] Levothyroxine labeling advises not to take levothyroxine within 4 hours of iron or calcium-containing agents. [2]
Medication Timing for Lisdexamfetamine
Lisdexamfetamine labeling does not provide a levothyroxine-specific timing separation requirement. [3] Practical timing separation is typically used to avoid shared GI/empty-stomach routine issues, while maintaining levothyroxine’s required empty-stomach administration. [2][3]
Monitoring Considerations
Cardiovascular monitoring for increased sympathomimetic effects may be advisable with combined therapy. [1] Clinical assessment for cardiac function changes is recommended when increased sympathomimetic effects occur. [1]
When Caution Should Be Increased
Thyroid hormone therapy should be used cautiously in patients with cardiovascular disease, because thyroid hormones can increase myocardial contractility and heart rate. [1] Amphetamine-class stimulants may cause cardiovascular adverse effects, so increased monitoring is appropriate in patients with cardiovascular risk. [1]
Medication Administration Approach
Levothyroxine should be administered first as prescribed for absorption (empty stomach, 30 to 60 minutes before food). [2] Lisdexamfetamine should then be administered according to its prescribed schedule, commonly later in the morning after breakfast, while maintaining levothyroxine separation from interfering agents (iron/calcium/antacids). [2][3] Levothyroxine should not be co-administered with calcium or iron supplements within 4 hours. [2]