{"entity":{"id":"radioactive-iodine","kind":"drug","name":"Radioactive iodine (I-131)","aka":[],"tldr":"The original targeted radiotherapy: thyroid cells soak up iodine, so radioactive iodine destroys leftover thyroid tissue and metastases while sparing everything else.","summary":"In use since 1946 for differentiated thyroid cancer; the archetype of theranostics (I-123 or I-131 scans image the same uptake). Roles: remnant ablation after thyroidectomy (now omitted in low-risk disease after ESTIMABL2, IoN, HiLo), adjuvant treatment of intermediate/high-risk disease, and treatment of iodine-avid metastases. Given after TSH stimulation (withdrawal or recombinant TSH). Salivary damage, secondary malignancy at high cumulative doses, and refractoriness in dedifferentiated tumours are the limits.","status":"approved","asOf":"2026-09-07","wikipedia":"https://en.wikipedia.org/wiki/Iodine-131","links":[{"label":"FDA label (DailyMed)","url":"https://dailymed.nlm.nih.gov/dailymed/search.cfm?query=Radioactive%20iodine"},{"label":"UniProt Q92911: sodium/iodide cotransporter (SLC5A5, NIS), the uptake route of iodide into thyroid cells","url":"https://www.uniprot.org/uniprotkb/Q92911/entry"}],"tags":[],"related":[],"cancers":["thyroid"],"sections":[],"technologies":["radioiodine-therapy","radioligand-therapy"],"targets":[],"drugs":[],"companies":[],"institutions":[],"pathways":[],"terms":["theranostics","rai-refractory","low-risk-dtc","radioiodine-term"],"trials":["hilo","estimabl2","ion-trial"],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":["Correction 23 Sept 2026: the record linked the somatostatin receptor 2 target, which belongs to the SSTR2 radioligands (Lutathera, RYZ101) and not to radioiodine. I-131 enters thyroid cells through the sodium-iodide symporter (SLC5A5, NIS), which has no target page in OnCo yet, so the record now names no target; the mechanism text says which transporter it uses. Found by the open drug engine, where the wrong link showed I-131 as an approved SSTR2 radioligand."],"brand":"Sodium iodide I-131","modality":"Radiopharmaceutical (beta/gamma emitter, natural uptake)","mechanism":"Sodium-iodide symporter (NIS) concentrates iodide in thyroid follicular cells; I-131 beta particles (mean path ~0.8 mm) irradiate the cell and neighbours; gamma emission enables imaging.","approvals":[{"region":"US","year":1951,"indication":"Hyperthyroidism and thyroid carcinoma (first radiopharmaceutical approval)"}],"mechanismSteps":["TSH stimulation upregulates the sodium-iodide symporter on thyroid cells","Oral I-131 is absorbed and concentrated in thyroid tissue and iodine-avid metastases","Beta decay deposits radiation within ~1 mm, killing the cells over weeks","Gamma emission allows a post-therapy scan to map uptake"],"dosing":{"route":"Oral capsule or solution","schedule":"1.1 GBq (30 mCi) for remnant ablation (HiLo); 3.7-7.4 GBq for adjuvant or metastatic treatment; low-iodine diet and TSH stimulation beforehand","monitoring":"Post-therapy whole-body scan; thyroglobulin; salivary and marrow function","source":"https://www.thyroid.org/professionals/ata-professional-guidelines/"},"toxicity":[{"event":"Sialadenitis / xerostomia","source":"https://www.thyroid.org/professionals/ata-professional-guidelines/","note":"Dose-dependent; common after repeated high-activity treatment"}],"access":[],"regulatoryEvents":[{"date":"1946","type":"approval","region":"US","note":"First therapeutic use in thyroid cancer (Seidlin); formal approval followed"}]},"route":"/drugs/radioactive-iodine/","neighbours":{"cancer":[{"id":"thyroid","kind":"cancer","name":"Thyroid cancer","route":"/cancers/thyroid/"}],"technology":[{"id":"radioiodine-therapy","kind":"technology","name":"Radioiodine therapy and whole-body iodine scanning","route":"/technologies/radioiodine-therapy/"},{"id":"radioligand-therapy","kind":"technology","name":"Radioligand therapy (beta emitters)","route":"/technologies/radioligand-therapy/"},{"id":"thyroid-cancer-markers","kind":"technology","name":"Thyroglobulin, calcitonin and CEA in thyroid cancer follow-up","route":"/technologies/thyroid-cancer-markers/"}],"term":[{"id":"low-risk-dtc","kind":"term","name":"Low-risk differentiated thyroid cancer (ATA risk)","route":"/terms/low-risk-dtc/"},{"id":"radioiodine-term","kind":"term","name":"Radioiodine therapy (I-131)","route":"/terms/radioiodine-term/"},{"id":"rai-refractory","kind":"term","name":"Radioiodine-refractory (RAI-R) thyroid cancer","route":"/terms/rai-refractory/"},{"id":"theranostics","kind":"term","name":"Theranostics","route":"/terms/theranostics/"}],"trial":[{"id":"estimabl2","kind":"trial","name":"ESTIMABL2","route":"/trials/estimabl2/"},{"id":"hilo","kind":"trial","name":"HiLo","route":"/trials/hilo/"},{"id":"ion-trial","kind":"trial","name":"IoN","route":"/trials/ion-trial/"}],"pairing":[{"id":"redifferentiation-rai","kind":"pairing","name":"MAPK inhibitor redifferentiation → radioiodine","route":"/pairings/redifferentiation-rai/"}],"roadmap":[{"id":"radiation-roadmap","kind":"roadmap","name":"Radiotherapy roadmap: X-rays → shaped beams → fewer fractions, particles and FLASH","route":"/roadmaps/radiation-roadmap/"}],"pathway":[{"id":"thyroid-cancer-signalling","kind":"pathway","name":"Thyroid cancer (KEGG map)","route":"/pathways/thyroid-cancer-signalling/"}]}}