Lamotrigine Does Not Affect Thyroid Function and Does Not Require Routine Thyroid Monitoring
Lamotrigine has no significant effect on thyroid hormone levels and does not require routine thyroid function monitoring in patients taking this medication. 1, 2, 3
Evidence Supporting No Thyroid Impact
The most comprehensive and recent systematic review and network meta-analysis from 2022, analyzing 35 studies with 4,135 participants and 8 different anti-seizure drugs, definitively concluded that lamotrigine was the anti-seizure drug with the least disruptive effect on thyroid hormone levels 1. This study found no significant changes in TSH, FT4, FT3, T4, or T3 levels with lamotrigine use.
Multiple additional studies consistently support this finding:
- A 2005 review examining glucuronosyltransferase-inducing antiepileptic drugs found that lamotrigine does not alter thyroid hormone homeostasis at all, or only minimally 2
- A 2008 study confirmed that newer antiepileptics including lamotrigine had no effect on thyroid hormones 4
- A 2015 review specifically stated that lamotrigine has not been shown to result in endocrine side effects 5
- A 2015 expert review confirmed no thyroid abnormalities with lamotrigine, in contrast to older antiepileptic drugs 3
Contrast with Other Antiepileptic Drugs
This stands in stark contrast to enzyme-inducing antiepileptic drugs:
- Carbamazepine and phenytoin significantly lower T4 and T3 levels 1
- Topiramate elevates TSH levels 1
- Oxcarbazepine may decrease FT4 and FT3 1
- Valproic acid and levetiracetam may cause subclinical hypothyroidism 1
The mechanism by which older antiepileptic drugs affect thyroid function involves induction of uridine diphosphate glucuronosyltransferases (UGT), enhanced metabolism, altered protein binding, or interference with the hypothalamic-pituitary-thyroid axis 2, 3. Lamotrigine does not induce these pathways.
Clinical Recommendation
No baseline or routine thyroid function testing is indicated specifically for lamotrigine therapy. Thyroid monitoring should only be performed if clinically indicated by symptoms or other risk factors unrelated to lamotrigine use (such as personal/family history of thyroid disease, autoimmune disorders, or pregnancy) 6.
The FDA drug label for lamotrigine does not include thyroid monitoring requirements 7, further supporting that this is not a clinically relevant concern with this medication.