Iron Supplements for RLS: Ferritin Targets and Dosing

Iron can ease restless legs syndrome (RLS), but only when your iron tests say you need it, and the target is higher than for ordinary iron deficiency. The American Academy of Sleep Medicine's 2025 guideline says adults with RLS should be offered iron if serum ferritin is 75 ng/mL or lower or transferrin saturation is below 20%, using either oral or intravenous (IV) iron, and IV iron only if ferritin is between 75 and 100 ng/mL. For children with RLS, the cutoff is a ferritin below 50 ng/mL. A ferritin that a lab calls "normal" can still be low enough to justify iron for RLS, which is why testing matters.

Do not start iron for restless legs on your own. Ask your doctor for fasting morning iron studies first; iron is not harmless for people whose stores are already adequate. This page covers why iron matters in RLS, the exact thresholds in the current guidelines, oral versus IV options, how to take oral iron so it has a fair chance of working, and what else the guideline recommends. For general dosing and side effects, see the main iron supplements guide.

Why Iron Matters in Restless Legs Syndrome

Restless legs syndrome causes an urge to move the legs, usually with uncomfortable sensations, that starts or gets worse during rest and in the evening and is relieved by movement. Researchers have linked RLS to iron deficiency in the brain, even in people whose blood counts look normal. The International Restless Legs Syndrome Study Group (IRLSSG) noted in its 2018 iron treatment guidelines that brain iron deficiency has been implicated in how RLS develops, and existing treatment guidelines already recommended iron when blood iron levels are low.

The NHLBI lists restless legs syndrome among the complications of untreated iron-deficiency anemia, and MedlinePlus lists it among the reasons a doctor may order a ferritin blood test. In practice, iron is one of the few RLS treatments that targets a possible underlying cause rather than only the symptoms.

The Current Guideline: Ferritin and Transferrin Saturation Thresholds

In January 2025, the American Academy of Sleep Medicine (AASM) published updated treatment guidance for RLS and periodic limb movement disorder in the Journal of Clinical Sleep Medicine. Its iron advice rests on a "good practice statement," meaning experts consider it essential to good care. The thresholds themselves come from consensus guidelines that the AASM notes have not been tested empirically.

Patient group	Iron study result	Iron route the AASM statement allows
Adults with RLS	Ferritin 75 ng/mL or lower, or transferrin saturation below 20%	Oral or IV iron
Adults with RLS	Ferritin between 75 and 100 ng/mL	IV iron only
Children with RLS	Ferritin below 50 ng/mL	Oral or IV iron
Adults with RLS and end-stage kidney disease	Ferritin below 200 ng/mL and transferrin saturation below 20%	IV iron sucrose suggested

The guideline stresses that these iron targets are different from those used for the general population. For comparison, many lab reference ranges flag ferritin as low only well below 75 ng/mL, so a result reported as "normal" may still qualify for iron if you have RLS.

How to get tested correctly

The AASM says clinicians should regularly test serum iron studies, including ferritin and transferrin saturation (calculated from serum iron and total iron-binding capacity), in every patient with clinically significant RLS. For the most reliable result:

• Have blood drawn in the morning.
• Avoid all iron-containing supplements and iron-rich foods for at least 24 hours before the draw.
• Ask for ferritin and transferrin saturation, not just a complete blood count.

Keep in mind that ferritin also rises with inflammation, infection, liver disease, obesity and other conditions, according to MedlinePlus. A ferritin that looks adequate during an illness may not reflect your true stores, which is one reason transferrin saturation is part of the threshold.

What the AASM Recommends for Iron in Adults With RLS

Among the treatments the AASM graded for adults with RLS and appropriate iron status (meaning the thresholds above are met):

Iron treatment	AASM strength	Certainty of evidence
IV ferric carboxymaltose (Injectafer)	Strong recommendation for use	Moderate
IV low molecular weight iron dextran	Conditional (suggested)	Very low
IV ferumoxytol (Feraheme)	Conditional (suggested)	Very low
Oral ferrous sulfate	Conditional (suggested)	Moderate
Oral ferrous sulfate in children	Conditional (suggested)	Very low

The same guideline gives strong recommendations for gabapentin enacarbil, gabapentin and pregabalin, and it now suggests against the standard use of the dopamine agonists pramipexole, ropinirole and rotigotine, and levodopa, mainly because of augmentation, a long-term worsening of symptoms. That shift makes it more important to correct iron status early, because iron is a treatment that does not carry the augmentation problem.

The guideline also says the first step in managing RLS should be addressing things that make it worse, such as alcohol, caffeine, sedating antihistamines, serotonergic and antidopaminergic medications, and untreated obstructive sleep apnea.

Oral Iron for RLS: Evidence and How to Take It

Oral iron is the usual starting point when ferritin is 75 ng/mL or lower and you can tolerate pills. The IRLSSG task force concluded that oral iron at 65 mg of elemental iron, the amount in one 325 mg ferrous sulfate tablet, is possibly effective for RLS in people with serum ferritin of 75 or less.

The key controlled trial is small but informative. In a 2009 randomized, double-blind, placebo-controlled study in Sleep Medicine, people with RLS and low-normal ferritin (average about 37 to 41 ng/mL at baseline) took oral iron or a matching placebo for 12 weeks. Symptom scores on the International Restless Legs Scale fell by about 10 points with iron versus about 1 point with placebo, and ferritin rose by about 25 ng/mL with iron versus 7.5 with placebo.

Practical tips

1. Agree on the dose. The guideline evidence centers on ferrous sulfate, typically one 325 mg tablet (65 mg iron). Your doctor may adjust the frequency.
2. Consider timing. Absorption studies show that a dose taken the day after another dose is absorbed 40% to 50% less, so some clinicians use every-other-day dosing. See the main guide for the trial details.
3. Space interacting drugs. Keep iron at least 4 hours from levothyroxine and 2 hours from tetracycline antibiotics.
4. Avoid black tea with your dose, since it reduces iron absorption.
5. Be patient. In the 2009 trial, benefits were measured at 12 weeks. Rebuilding iron stores generally takes months.
6. Retest. Ask for repeat ferritin and transferrin saturation, again in the morning after a 24-hour iron break, to see whether you have reached the target.

Oral iron has limits. Only a small share of each dose is absorbed, and gastrointestinal side effects such as constipation and nausea are common. If ferritin will not budge after a fair trial, or if your ferritin is already between 75 and 100 ng/mL, IV iron becomes the option.

IV Iron for RLS

The AASM's only strong iron recommendation in RLS is for IV ferric carboxymaltose in adults with appropriate iron status. The IRLSSG reported that 1,000 mg of ferric carboxymaltose is effective for moderate to severe RLS in people with serum ferritin below 300 ng/mL and said it could be used as a first-line treatment in adults. Note the difference: the IRLSSG described trial evidence above the AASM threshold, while the AASM's 2025 statement limits IV iron to adults with ferritin up to 100 ng/mL or transferrin saturation below 20%. Your sleep specialist will apply the current guideline.

Ferric carboxymaltose is FDA-approved for iron-deficiency anemia in patients who cannot tolerate or did not respond to oral iron, and for certain other conditions; its use specifically for RLS is based on guideline recommendations rather than a separate FDA indication. Its label carries a boxed warning for symptomatic hypophosphatemia, a drop in blood phosphate that can be severe and prolonged. Other IV products the AASM suggests are low molecular weight iron dextran, which requires a test dose and carries a boxed warning for anaphylactic-type reactions, and ferumoxytol, which carries a boxed warning for serious hypersensitivity reactions. Read more about the process, products and side effects on our iron infusion page.

	Oral iron	IV iron
When the AASM statement allows it	Ferritin 75 ng/mL or less, or transferrin saturation below 20%	Same, plus ferritin 75 to 100 ng/mL
Evidence strength in adults	Conditional, moderate certainty (ferrous sulfate)	Strong, moderate certainty (ferric carboxymaltose)
Typical course	Daily or alternate-day tablets for months	One or two infusions per course
Main drawbacks	Stomach side effects, slow, low absorption	Clinic visit, cost and insurance approval, rare serious allergic reactions, low phosphate with ferric carboxymaltose

Applying the Thresholds: Three Examples

These hypothetical cases show how the AASM good practice statement sorts adults with RLS. Real decisions also weigh symptoms, other conditions and patient preference.

Iron studies	Where the guideline places it	Likely next step
Ferritin 38 ng/mL, transferrin saturation 22%	Ferritin 75 or less: oral or IV iron	Trial of oral ferrous sulfate with retesting, or IV iron if pills are not tolerated
Ferritin 88 ng/mL, transferrin saturation 25%	Ferritin 75 to 100: IV iron only	Discuss IV ferric carboxymaltose or another IV iron; oral iron not advised in this range
Ferritin 140 ng/mL, transferrin saturation 30%	Above thresholds	Iron not indicated; focus on aggravating factors and other guideline treatments

A low transferrin saturation (below 20%) also qualifies an adult for oral or IV iron even when ferritin is above 75, which matters when inflammation has pushed ferritin up.

Repeat Treatment and Long-Term Monitoring

Iron stores can drift down again after successful treatment, especially if the original cause of iron loss continues. The IRLSSG task force published consensus algorithms that include recommendations on when to repeat iron treatment, and the AASM asks clinicians to test iron studies regularly in people with clinically significant RLS. In practice, that means periodic morning ferritin and transferrin saturation checks, with another course of oral or IV iron if values fall back into the treatment range and symptoms return.

RLS in Pregnancy and in Children

RLS is common in pregnancy, and the AASM reminds prescribers to consider each treatment's pregnancy-specific safety profile. Because iron needs rise in pregnancy anyway, checking iron studies is a natural first step. For prenatal iron guidance, see iron supplements for pregnancy.

In children with RLS, the AASM suggests ferrous sulfate when ferritin is below 50 ng/mL, with very low certainty of evidence. The IRLSSG found only lower-quality studies in children and said evidence was insufficient to draw conclusions on oral or IV iron efficacy in kids. Pediatric dosing must come from the child's doctor, and iron products must be stored where children cannot reach them; accidental iron overdose is a leading cause of fatal poisoning in children under 6. If a child swallows iron pills, call Poison Control at 1-800-222-1222.

Other Steps That Help Restless Legs

Iron works best as part of a broader plan. Based on the AASM guideline's first-line advice:

• Cut back on alcohol and caffeine, especially later in the day.
• Review your medications with your doctor. Sedating antihistamines, many antidepressants that act on serotonin, and medicines that block dopamine can worsen RLS.
• Get evaluated for obstructive sleep apnea if you snore, stop breathing at night or wake unrefreshed.
• If symptoms continue despite iron, ask about guideline-recommended medicines such as gabapentin, gabapentin enacarbil or pregabalin, or about bilateral high-frequency peroneal nerve stimulation, which the AASM also suggests.

Common Mistakes With Iron for RLS

• Accepting "your iron is normal." A ferritin of 50 ng/mL may be inside a lab's normal range yet below the RLS threshold of 75.
• Testing right after an iron pill. Iron taken within the past day can distort results; the guideline asks for a 24-hour break.
• Taking iron without testing. If your ferritin is already above 100 ng/mL and transferrin saturation is normal, iron is not recommended for RLS and can be harmful if you have iron overload.
• Stopping too early. Give oral iron months, not weeks, and recheck before deciding it failed.
• Ignoring the cause of low iron. In adults, low ferritin should prompt a look for blood loss or poor absorption. See the low ferritin guide.