Restless legs at night are driven by a combination of brain chemistry and body clock timing. The core problem is a dip in dopamine signaling in the brain that naturally occurs in the evening, which disrupts the circuits controlling movement and sensation in your legs. For some people this is a one-off annoyance triggered by caffeine or a medication. For others, it’s a chronic condition rooted in genetics, iron levels, or an underlying health problem.
How Dopamine and Iron Work Together
The main biological driver of restless legs syndrome (RLS) is a disruption in how dopamine works in the basal ganglia, a group of structures deep in the brain that help regulate movement. Brain imaging studies show that people with RLS have fewer dopamine receptors in a key region called the striatum, which means dopamine signals don’t land as effectively. When this signaling falters, abnormal activity ripples through a network connecting the basal ganglia to the motor cortex, and your legs respond with that creeping, pulling urge to move.
Iron plays a direct role because your brain needs it to produce dopamine in the first place. It’s also essential for making neurotransmitters and proteins in muscle cells. When iron stores drop, dopamine production suffers, and RLS symptoms can appear or worsen. Doctors often check a blood marker called ferritin, which reflects your body’s stored iron. A ferritin level at or below 50 micrograms per liter is the threshold where iron supplementation is recommended for RLS, even if that number technically falls within the “normal” range on a standard lab report. Many people with restless legs have ferritin levels that look fine on paper but are low enough to starve the brain of the iron it needs for smooth dopamine function.
Why Symptoms Get Worse at Night
It’s not just that you notice your legs more when you’re lying still. There is a genuine circadian (body clock) pattern to RLS that makes symptoms worse in the evening and nighttime hours, independent of whether you’re resting or sleep-deprived. Studies tracking dopamine-related chemicals in the spinal fluid of RLS patients found that dopamine metabolism swings significantly between day and night, with lower levels in the evening corresponding to peak symptom times.
This timing lines up with the declining portion of your core body temperature curve, a reliable marker of your circadian cycle. As your body cools toward its nighttime low, your nervous system becomes more excitable. Research measuring pain thresholds in RLS patients found they were significantly more sensitive to stimulation at night compared to the morning, particularly in the small nerve fibers that carry pain and discomfort signals. In other words, your legs aren’t just restless at night because you’re finally sitting down. Your nervous system is genuinely more reactive.
Melatonin likely plays a role too. As melatonin rises in the evening to prepare you for sleep, it suppresses dopamine secretion in several areas of the brain. For someone whose dopamine system is already running low, that melatonin-driven dip can push things past the tipping point into full-blown symptoms.
Genetics and Family History
Up to 60% of people with primary RLS report a family history of the condition, and some populations show rates as high as 85%. Researchers have identified several genes linked to RLS risk, with variants in three genes (PTPRD, BTBD9, and MEIS1) showing the strongest associations. These genes are involved in limb development, iron regulation, and nervous system function. None of them alone “causes” RLS, but inheriting certain combinations increases your vulnerability, especially when combined with low iron or other triggers.
If one or both of your parents had restless legs, your chances of developing it are substantially higher, and symptoms tend to start earlier in life compared to people without a family connection.
Medications That Trigger or Worsen Symptoms
Several common medications can bring on restless legs or make existing symptoms noticeably worse. The main culprits fall into three categories:
- Antihistamines: Many over-the-counter sleep aids and allergy medications (like diphenhydramine, the active ingredient in products marketed for sleep) block dopamine activity and can trigger or intensify RLS.
- Antidepressants: Certain antidepressants, particularly SSRIs, are well-documented triggers. In clinical observations, reintroducing an SSRI after stopping it led to a clear worsening of RLS symptoms.
- Dopamine-blocking drugs: Anti-nausea medications and antipsychotics that block dopamine receptors can provoke symptoms directly, since dopamine suppression is the core mechanism behind RLS.
If your restless legs started or got worse around the time you began a new medication, that connection is worth exploring with your prescriber. Switching to an alternative in the same class can sometimes resolve the problem entirely.
Health Conditions Linked to Restless Legs
RLS can exist on its own (primary RLS), but it also shows up alongside several other conditions. Kidney disease is one of the strongest associations. Among patients on dialysis, 7 to 22% develop RLS, a rate substantially higher than the 2 to 10% seen in the general population. The connection likely involves impaired iron metabolism and the buildup of waste products that affect nerve function.
Pregnancy is another common trigger. About one in five pregnant women develops RLS, with symptoms peaking in the third trimester. The good news is that pregnancy-related RLS typically resolves around delivery. The cause is thought to involve a combination of dropping iron and folate stores, hormonal shifts, and the increased circulatory demands of late pregnancy.
Diabetes-related nerve damage in the legs, peripheral neuropathy from other causes, and sleep disorders also overlap frequently with RLS. Around 80% of people with RLS also experience periodic limb movements in sleep, involuntary jerking or twitching of the legs that occurs every 20 to 40 seconds during the night. These movements can fragment sleep without fully waking you, leaving you exhausted the next day even if you thought you slept through the night.
Lifestyle Factors That Make It Worse
Caffeine, alcohol, and nicotine can all amplify restless legs symptoms. Caffeine increases nervous system arousal, which compounds the nighttime hyperexcitability that’s already a problem in RLS. Alcohol disrupts sleep architecture and has been directly linked to worsening symptoms. Heavy or prolonged alcohol use is associated with nerve damage in the legs, which can trigger secondary RLS. Nicotine is a stimulant that affects dopamine pathways, and while it briefly boosts dopamine, the rebound effect as it wears off can leave your system more depleted.
Prolonged inactivity also plays a role. Long flights, desk work, or evenings on the couch tend to bring symptoms out, partly because stillness removes the sensory input that normally keeps your movement circuits quiet. Light stretching, walking, or other moderate activity in the hours before bed can reduce symptom severity for many people, likely by priming dopamine release and calming nerve excitability before the circadian dip takes hold.
Iron Supplementation as a First Step
Because low iron is one of the most treatable causes of restless legs, checking your ferritin level is the single most useful starting point. If your level is at or below 50 micrograms per liter, oral iron supplements taken on an empty stomach (or with vitamin C to improve absorption) can meaningfully reduce symptoms over the course of several weeks. This threshold is lower than what would trigger a diagnosis of anemia, which is why many people with RLS-related iron deficiency are told their bloodwork looks normal.
Iron supplementation won’t help everyone, particularly if your ferritin is already well above 50 or if your RLS is driven primarily by genetics or medication side effects. But given how common low iron is as a contributor, especially in women, vegetarians, and frequent blood donors, it’s the simplest and most overlooked fix.