Lemon balm is generally well tolerated, but several groups of people should avoid it or use it cautiously. The most important are people with thyroid conditions, anyone taking sedative medications, people with glaucoma, and those preparing for surgery. Here’s a closer look at each group and why lemon balm poses a problem.
People With Thyroid Conditions
Lemon balm directly affects thyroid function. It blocks the binding of thyroid-stimulating hormone (TSH) to its receptors, which changes how much thyroid hormone your body produces. This makes it a real concern for anyone already managing a thyroid disorder, whether overactive or underactive.
The mechanism is somewhat complex. Lemon balm appears to increase circulating levels of the active thyroid hormones T3 and T4, likely by reducing blood lipid levels and boosting the protein that carries thyroid hormones in the blood. The rise in free thyroid hormones then signals the pituitary gland to dial back TSH production through a natural feedback loop. For someone whose thyroid levels are already carefully managed with medication, this interference can throw off the balance your doctor has worked to establish.
If you take levothyroxine or another thyroid hormone replacement, lemon balm may interfere with its action. The evidence supporting this interaction is still preliminary, but the biological mechanism is plausible enough that most references flag it as a combination to avoid, or at minimum to discuss with whoever manages your thyroid care.
People Taking Sedative Medications
Lemon balm has mild sedative properties on its own. That calming effect is part of why people take it for anxiety and sleep. But when combined with prescription sedatives, the effects can stack in ways that become risky. The concern isn’t just extra drowsiness. Lemon balm combined with sedative drugs can slow breathing and cause excessive sedation.
This applies to a broad category of medications classified as central nervous system depressants: sleep aids, anti-anxiety drugs, certain anticonvulsants, and similar prescriptions. If any of your medications carry a warning about drowsiness, combining them with lemon balm raises the chance of compounded effects. The interaction is rated as moderate, meaning it’s not necessarily dangerous in every case but warrants real caution.
People With Glaucoma
Anecdotal reports suggest lemon balm may increase intraocular pressure, the fluid pressure inside the eye. For most people, a slight change in eye pressure is meaningless. For someone with glaucoma, it’s a different story. Elevated intraocular pressure is the primary driver of optic nerve damage in glaucoma, and even small increases can accelerate vision loss.
The concern extends to medication effectiveness. If lemon balm raises eye pressure, it could work against the glaucoma medications you’re taking to lower it. The evidence here is based on anecdotal accounts rather than controlled studies, so it’s not a confirmed effect. Still, given that the potential consequence is irreversible vision damage, most clinical references list glaucoma as a reason to avoid lemon balm.
Anyone Scheduled for Surgery
The American Society of Anesthesiologists recommends stopping all herbal medicines at least two weeks before any surgical procedure. Lemon balm is no exception. Its sedative properties can interact unpredictably with anesthesia and other drugs used during and after surgery. The two-week window gives your body enough time to fully clear the herb’s active compounds.
This isn’t a lemon balm-specific warning so much as a general precaution that applies especially well to lemon balm because of its effects on the central nervous system. If you have a procedure coming up, mention your lemon balm use during your pre-surgical consultation, even if it seems minor.
Pregnant and Breastfeeding Women
No data exist on whether lemon balm’s active components pass into breast milk, and there’s limited safety information for pregnant women. The absence of evidence isn’t the same as evidence of harm, but it does mean no one can tell you with confidence that it’s safe during pregnancy or nursing.
There is a small silver lining for breastfeeding mothers: lemon balm has been used safely in combination with other herbs to treat colic and digestive issues in infants directly, which suggests the much smaller amounts that might pass through breast milk are unlikely to cause harm at normal doses. Some sources also note lemon balm as a traditional galactogogue, an herb thought to support milk production, though the evidence for this is weak. Still, the lack of direct safety data means most experts recommend caution.
Common Side Effects in Otherwise Healthy People
Even if you don’t fall into any of the groups above, lemon balm can occasionally cause minor side effects. In clinical trials, participants have reported headaches, dizziness, bloating, nausea, abdominal pain, decreased appetite, and wheezing. These effects are uncommon and were often reported at similar rates among people taking a placebo, which suggests some of them may not be caused by the herb at all. No serious adverse events have been reported in studies, and lab tests typically show no significant changes.
Children appear to tolerate lemon balm well. In a study of primary school children taking lemon balm and valerian root extracts over seven weeks, only two children experienced mild, temporary side effects. Previous research in children under 12 found similar tolerability for restlessness and sleep difficulties. That said, “well tolerated in studies” and “appropriate for unsupervised use” are different things, especially for younger children where dosing is less established.
The Bottom Line on Interactions
The groups most clearly affected are people with thyroid disorders, those on sedative medications, people managing glaucoma, and anyone facing surgery within the next two weeks. Pregnant and breastfeeding women fall into a gray zone where data simply doesn’t exist to confirm safety. For everyone else, lemon balm has a strong safety profile with only occasional, mild side effects. The key risk isn’t lemon balm itself but what it does in combination with existing conditions or medications that affect the same systems.