Lemon balm (Melissa officinalis) is a gentle, calming herb often used for restlessness, anxiety, and digestive upset. But when it comes to thyroid health, this herb has a unique consideration: it may act as an antagonist to medications for hypothyroidism.
What Does "Antagonist" Mean?
In pharmacology, an antagonist is something that blocks or reduces the effect of another substance. In this case, lemon balm may interfere with the action of thyroid hormones or medications like levothyroxine, which are prescribed to people with hypothyroidism.
How Lemon Balm Interacts with the Thyroid
Research suggests that certain compounds in lemon balm can:
- Inhibit TSH binding: TSH (thyroid-stimulating hormone) helps regulate thyroid function. Lemon balm may interfere with TSH binding to thyroid cells.
- Reduce thyroid hormone activity: Some studies indicate that lemon balm might inhibit the conversion of T4 (thyroxine) to T3 (the more active thyroid hormone).
These actions are why lemon balm is sometimes described as having thyrosuppressive activity.
Why This Is a Concern for Hypothyroid Conditions
For people with hypothyroidism, the body doesn’t produce enough thyroid hormone. Medications like levothyroxine work to restore balance. If lemon balm counteracts that effect — even slightly — it could reduce the effectiveness of the medication. This may leave symptoms like fatigue, low mood, weight gain, and slowed metabolism unresolved or worsened.
What the Evidence Says
Most of the evidence for this interaction comes from in vitro (test tube) and animal studies. While the exact impact in humans isn’t fully understood, thyroid hormone balance is delicate, and even small disruptions can have noticeable effects. That’s why many herbalists and practitioners recommend avoiding lemon balm if you are taking thyroid medication, unless guided by a knowledgeable healthcare provider.
The Takeaway
Lemon balm is a wonderful herb for calming the nervous system and supporting digestion, but if you are taking thyroid medication for hypothyroidism, it’s best to approach with caution. Always consult your healthcare provider before adding lemon balm to your routine, especially in therapeutic doses. Herbs are powerful allies — and knowing how they interact with your body ensures they’re used safely and effectively.