Restless legs and arms are most commonly caused by a condition called restless legs syndrome (RLS), which stems from disrupted dopamine signaling in the brain and, in many cases, low iron levels. While the name focuses on the legs, roughly 21% to 57% of people with more severe RLS also experience the same uncomfortable sensations in their arms. The underlying triggers range from genetics and nutrient deficiencies to medications, pregnancy, and kidney disease.
How Dopamine and Iron Drive the Symptoms
The core problem in RLS is a malfunction in dopamine, the brain chemical that helps regulate movement and sensory processing. Dopamine signals pass through a region called the basal ganglia, which acts as a gatekeeper between sensory input and motor output. When dopamine signaling drops in this area, your brain struggles to filter out low-level sensory signals that it would normally ignore. The result is that crawling, pulling, or tingling sensation that creates an overwhelming urge to move.
The dopamine picture is more complicated than a simple shortage, though. Brain imaging studies show that people with RLS actually overproduce dopamine but have reduced activity at the receptors that receive it. Think of it as a system that’s shouting louder because the listeners have gone partially deaf. This mismatch helps explain why the condition worsens over time and why certain treatments eventually stop working.
Iron plays a critical role because your brain needs it to manufacture dopamine. Research published in Neurology found that cells in the substantia nigra, a key dopamine-producing region, have impaired iron absorption in people with RLS. Animals deprived of brain iron show measurably fewer dopamine receptors and a weaker behavioral response to dopamine stimulation. This is why a ferritin level (a blood marker for iron stores) below 50 to 75 ng/mL is considered a treatable trigger, even if it falls within the “normal” range on a standard lab report.
Why Symptoms Spread to the Arms
RLS almost always begins in the legs, and for many people it stays there. But as the condition becomes more severe, the restless sensations can migrate upward. Studies estimate that arm involvement occurs in 21% to 57% of cases, depending on disease severity. This spread typically happens later in the course of the condition, often years after leg symptoms first appeared. Even when the arms are affected, the legs usually remain the most bothersome area.
The pattern matters for getting the right diagnosis. If uncomfortable sensations started in your arms without ever involving your legs, the cause is less likely to be classic RLS and more likely to be peripheral neuropathy or another condition. True restless arms syndrome, as researchers have labeled it, follows from and accompanies leg involvement.
Genetic Factors
RLS runs in families. If one of your parents had it, your risk is significantly higher, especially if symptoms began before age 40. Genome-wide studies have identified several gene variants that increase susceptibility, with the most consistent findings linked to genes involved in limb development and iron regulation. One variant in a gene called BTBD9 raised the odds of developing RLS by about 47% to 56% across multiple study populations. Variants in another gene, MEIS1, showed similar effect sizes. These aren’t rare mutations; they’re common genetic variations that each nudge your risk upward, and having several of them together can meaningfully increase your chances.
Medical Conditions That Trigger Symptoms
Several health conditions independently cause or worsen restless legs and arms by disrupting dopamine pathways, depleting iron, or both.
Kidney disease is one of the strongest medical triggers. Among patients with end-stage renal disease, about 27% have RLS. The connection involves iron deficiency, anemia, and the accumulation of waste products that dialysis doesn’t fully clear. All of these factors impair dopamine function.
Pregnancy triggers RLS in roughly 14% to 25% of pregnant women, likely due to rapidly falling iron and folate stores combined with hormonal shifts. Symptoms tend to peak in the third trimester and typically resolve within weeks after delivery, though some women find they return with subsequent pregnancies.
Iron deficiency anemia from any cause (heavy periods, dietary gaps, blood donation, gastrointestinal bleeding) can trigger symptoms even in people with no family history of RLS. Thyroid disorders and diabetes-related nerve damage are also recognized triggers.
Medications That Make It Worse
A surprisingly long list of common medications can trigger or intensify restless sensations. The Restless Legs Syndrome Foundation flags several entire drug classes:
- Antidepressants: All classes can worsen RLS, including SSRIs and SNRIs. This is one of the most common medication-related triggers.
- Antihistamines: Especially those containing diphenhydramine, the active ingredient in Benadryl and many over-the-counter sleep aids like Tylenol PM, Advil PM, Unisom, and Sominex.
- Anti-nausea medications: Many drugs prescribed for nausea block dopamine receptors directly.
- Antipsychotics: Both older and newer-generation antipsychotics can significantly worsen symptoms.
The antihistamine connection catches many people off guard. If your restless legs seem worse on nights when you take an over-the-counter sleep aid or cold medication, diphenhydramine is a likely culprit. Checking ingredient labels for diphenhydramine or doxylamine can help you identify hidden sources.
Caffeine, Alcohol, and Nicotine
Heavy caffeine intake is a recognized trigger. In one documented case, a 45-year-old woman drinking 10 to 12 cups of coffee per day and eating multiple coffee-flavored chocolates daily developed significant RLS symptoms. After she eliminated caffeine, her pulling sensations improved substantially, though she dealt with withdrawal symptoms like headaches and difficulty concentrating for a period. Moderate caffeine use doesn’t cause problems for everyone, but if your symptoms are poorly controlled, cutting back is worth testing.
Alcohol and nicotine are also associated with increased symptom severity, though the mechanisms are less clearly mapped. Alcohol disrupts sleep architecture, which may worsen the nighttime pattern of RLS, while nicotine is a stimulant that can increase nervous system excitability.
How to Tell RLS From Nerve Damage
Peripheral neuropathy, which involves damage to the nerves in your hands and feet, can feel similar enough to cause confusion. Three key differences help separate them:
- Type of sensation: RLS produces an internal urge to move, often described as crawling, pulling, or aching deep inside the limb. Neuropathy causes sharp, burning, or electrical pain, often described as pins and needles on the surface.
- Timing: RLS symptoms worsen at rest, particularly in the evening and at night. Neuropathy pain can strike at any time of day and doesn’t follow the same rest-related pattern.
- Response to movement: Getting up and walking or stretching relieves RLS almost immediately. Movement does not reliably help neuropathy pain and can sometimes make it worse.
It’s also possible to have both conditions at the same time, since diabetes and iron deficiency can cause each independently. If stretching provides temporary relief but a burning or electrical quality to the pain persists, both may be contributing.
What Keeps Symptoms Coming Back at Night
The evening and nighttime worsening of RLS isn’t just about being still. Dopamine levels in the brain naturally fluctuate on a circadian rhythm, dipping in the late evening. For someone whose dopamine signaling is already compromised, this normal dip pushes the system below a functional threshold. Iron metabolism also follows a circadian pattern, with serum iron levels dropping in the evening. These two cycles converge to make the hours between about 10 PM and 2 AM the worst window for most people, which is exactly why RLS is so disruptive to sleep.