IV Iron for RLS: Four and Twelve Weeks

If you have received an iron infusion for restless legs syndrome, keep the infusion date with your nighttime symptom record. Note when the urge to move starts, how long it lasts and how sleep is affected. Bring that record to the agreed follow-up.

What did four weeks show?

The 2017 trial¹ randomized 110 adults, including 90 women, to one 1,000-mg ferric carboxymaltose infusion or placebo. Participants met the study’s moderate-to-severe RLS, low-iron and nonanemic criteria.¹

The four-week primary comparison was −2.46 points on the International Restless Legs Severity Scale (95% CI −5.93 to 1.02; P=.163). It did not establish superiority. Negative differences favor the infusion.²

What changed at twelve weeks?

The secondary twelve-week difference was −4.66 points (95% CI −8.59 to −0.73; P=.021). This was a later, nominal secondary finding after a failed primary test, not a confirmed response timetable.²

Only 87 completed; analyses carried earlier observations forward for missing scores. Vifor funded the trial and employed three authors. These findings do not establish when an individual should respond or receive another infusion.¹

The 2025 AASM guideline strongly recommends IV ferric carboxymaltose for adults with RLS and appropriate iron status, with moderate-certainty evidence. That recommendation considers several trials. This one trial’s early result should not be read as a finding that IV iron never helps RLS.³

How should follow-up be arranged?

The guideline recommends regular ferritin and transferrin-saturation assessment for clinically significant RLS. It also advises addressing aggravating medicines, caffeine, alcohol and untreated sleep apnea. Ask which factors apply to you and how symptoms and iron results will be reviewed together.³

US Injectafer prescribing information lists certain iron-deficiency-anemia and heart-failure indications, not RLS. RLS treatment is off-label in the US. A research dose does not replace an individual prescribing plan.⁴

The August 2026 label carries a boxed warning for severe, prolonged low blood phosphate, which can cause bone softening and fractures. It calls for phosphate testing before repeat treatment in at-risk patients and anyone receiving another course within three months. New fatigue, muscle weakness or bone pain should be reported, rather than assumed to be persistent RLS. Serious allergic reactions also require observation during treatment and for at least 30 minutes afterward, until stable.⁴

Ask the team to write down your review date, who will interpret test results and how to contact them sooner if symptoms or unwanted effects change. Keep changes to existing medicines with the prescriber.

Did I Do That in My Sleep? explains “The Legs That Won’t Settle” and “Why the Restless-Legs Advice Changed.” Those sections help describe an awake urge to move, its timing and relief with movement, while distinguishing it from kicks observed during sleep. Use that description alongside your follow-up plan.