25I-NBF (2C-I-NBF, NBF-2C-I, Cimbi-21) is a derivative of the phenethylamine hallucinogen 2C-I, which acts as a highly potent partial agonist for the human 5-HT_2A receptor, with bias towards the β-arrestin 2 coupled signalling pathway. It has been studied in its ¹¹C radiolabelled form as a potential ligand for mapping the distribution of 5-HT_2A receptors in the brain, using positron emission tomography (PET).

25I-NBF is illegal in Hungary, Japan, Latvia, and Vermont.

The Riksdag added 25I-NBF to Narcotic Drugs Punishments Act under Swedish schedule I ("substances, plant materials and fungi which normally do not have medical use") as of January 26, 2016, published by Medical Products Agency (MPA) in regulation HSLF-FS 2015:35 listed as 25I-NBF, and 2-(4-jodo-2,5-dimetoxifenyl)-N-(2-fluorobensyl)etanamin.

This substance is a Class A drug in the United Kingdom as a result of the N-benzylphenethylamine catch-all clause in the Misuse of Drugs Act 1971.