Research chemicalResearch chemicalPhenethylaminePsychedelic

25B-NBF

Also known as NBF-2C-B · 2C-B-NBF

Written by enwyReviewed 5 Aug 20261 sources0 comments

25B-NBF is a potent serotonergic psychedelic, the N-(2-fluorobenzyl) analogue of 2C-B and a close relative of 25B-NBOMe. Active in the low milligram to sub-milligram range and typically taken sublingually or on blotter. It is one of the most poorly studied members of the N-benzyl phenethylamine class; its narrow safety margin and strong vasoconstriction make it dangerous.

01 Overview

25B-NBF is the fluorinated N-benzyl analogue of 2C-B, structurally analogous to the NBOMe and NBOH series. As a high-affinity 5-HT2A agonist it is active at very low doses and is difficult to dose accurately, particularly on blotter where it can be confused with LSD or other N-benzyl compounds.

Human pharmacology and toxicology are almost entirely uncharacterised. Because it shares the 5-HT2A mechanism of the NBOMe series, which has caused severe vasoconstriction, seizures, hyperthermia and deaths, 25B-NBF should be assumed to carry similar hazards. The narrow margin between an active and a harmful dose is the key concern.

02 Mechanism

Potent agonist at serotonin 5-HT2A receptors; the N-2-fluorobenzyl group increases receptor affinity relative to the parent 2C-B.

03 Dosing

Tier	Dose	Route	Notes
Threshold	200–500 mcg	Sublingual	First noticeable effects; sensitivity varies and blotter dosing is imprecise.
Common	500–1500 mcg	Sublingual	Anecdotal range; not clinically validated.
Strong	1500–2500 mcg	Sublingual	Higher doses sharply increase the risk of severe adverse effects.

04 Effects

Effect	Magnitude	Evidence
Visual distortionColour enhancement, patterning and visual movement reported by users.	strong	Anecdotal
Altered mood and cognitionEmotional and cognitive shifts typical of classical psychedelics.		Anecdotal
StimulationPhysical stimulation and restlessness commonly reported with N-benzyl phenethylamines.		Anecdotal

05 Side effects

Effect	Severity	Frequency	Evidence
Anxiety and confusionOverwhelming or frightening experiences, especially with unexpected potency.	Moderate	Common	Anecdotal
Peripheral vasoconstrictionMarked vasoconstriction causing cold, painful extremities; the related NBOMe class has caused ischaemic injury.	Severe	Common	Anecdotal
SeizuresConvulsions have been reported across the N-benzyl phenethylamine families after overdose.	Life-threatening	Uncommon but documented in the class	Anecdotal

06 Legal status

United Kingdom

Class A / Psychoactive Substances Act

N-benzyl phenethylamines are controlled. · as of Jan 2026

United States

Possibly controlled as an analogue

May be treated as a controlled substance analogue under the Federal Analogue Act. · as of Jan 2026

07 References

25B-NBF and NBF-series reportsPubMed search

08 Discussion0 comments

Create account

Discussion is moderated. No sourcing, vendor names or price talk — those comments are removed, and repeat posts are banned.

This page is reference information, not medical advice. Doses and protocols are documented as they appear in the clinical literature and in practice — describing them is not a recommendation to use them. Countermeasures listed here are not a substitute for a physician. Legal status varies by jurisdiction and changes.