Restless legs syndrome is usually discussed as a standalone neurological condition, tied to iron deficiency, kidney disease, or genetics. But a large new analysis published in the International Journal of Neuropsychopharmacology points to a less-discussed trigger hiding in plain sight: common psychiatric medications.
What the Data Showed
Researchers drew on AMSP, a multinational pharmacovigilance program that has tracked adverse drug reactions among psychiatric inpatients across German-speaking countries since 2001. Analyzing records from January 2001 through December 2016, they identified every case of newly diagnosed, severe restless legs syndrome that clinicians attributed to a psychotropic medication.
Out of 340,099 monitored inpatients, the team found 67 cases of drug-induced RLS severe enough to be flagged — a relative frequency of roughly 0.02%. Small as that number sounds, the pattern behind it was striking: more than 80% of all cases traced back to just two drugs.
Two Drugs, Most of the Cases
The antidepressant mirtazapine was implicated in 39 of the 67 cases, and the antipsychotic quetiapine in another 16 — together accounting for the large majority of drug-triggered RLS identified across a 15-year, multinational surveillance program. No other individual psychotropic medication came close to that share.
Two details stood out about how these cases unfolded. First, the restless legs symptoms typically appeared at low doses of the drug — not at the higher doses often assumed to carry more side-effect risk. Second, onset was often fast: most cases emerged within one or two days of starting the medication or changing its dose, rather than building gradually over weeks.
For a patient starting mirtazapine for depression or quetiapine for sleep, mood, or psychotic symptoms, that timeline means a new, uncomfortable urge to move the legs — particularly in the evening or at night — could plausibly show up almost immediately, and be mistaken for anxiety, akathisia, or simple restlessness rather than recognized as RLS.
A Shared Mechanism: Histamine
Mirtazapine and quetiapine don't share an obvious pharmacological profile — one is an antidepressant, the other an antipsychotic. But the study's authors point to a property they do share: both are potent antihistamines at low doses, blocking histamine H1 receptors even before their primary therapeutic effects kick in.
The researchers propose that this shared antihistaminergic action may be a "crucial common denominator" driving secondary RLS across otherwise different drug classes. Histamine signaling has documented links to dopaminergic pathways in the brain, and dopamine dysfunction is already the central mechanism thought to underlie restless legs syndrome generally — which is why dopamine-related therapies have long been a mainstay of RLS treatment.
If the histamine hypothesis holds up, it would suggest a way to predict which future psychiatric medications might carry similar risk, simply by looking at their antihistaminergic potency.
Why This Matters Beyond Psychiatry
RLS symptoms — an irresistible urge to move the legs, often with an uncomfortable crawling or aching sensation that worsens at rest and in the evening — are already underrecognized in general medicine. When they emerge shortly after starting a psychiatric medication, they're especially easy to misattribute to the underlying condition being treated, to anxiety, or to a movement side effect like akathisia, which can look similar but has a different cause and treatment.
That distinction matters clinically. Akathisia is typically addressed by adjusting the antipsychotic or antidepressant regimen itself, while medication-induced RLS may resolve with dose reduction, switching to a less antihistaminergic alternative, or standard RLS management such as iron repletion when relevant.
What This Means for Patients
Anyone who develops a new urge to move their legs — particularly one that worsens at night or with rest — shortly after starting or adjusting a dose of mirtazapine, quetiapine, or a similar antihistaminergic psychiatric medication should mention it to their prescriber rather than assuming it's unrelated anxiety or a normal side effect to tolerate. Because these cases tend to emerge within days rather than weeks, the connection to a recent medication change is often traceable if patients and clinicians know to look for it.
The finding doesn't mean these medications should be avoided broadly — both remain effective, widely used treatments for serious conditions. But recognizing restless legs syndrome as a possible, identifiable side effect — rather than a mysterious new symptom — could help patients get faster relief, whether through a dose adjustment, a medication switch, or targeted treatment of the RLS itself.
