This is an extreme tale of caution, as I almost extinguished my flame, my light, my life - 4 times within 2 weeks with this material . To give context, I have quite a extensive history with most classes of compounds. I've worked with many phenethylamines and tryptamines, as well as several stimulants and opiates.
Furanylfentanyl
Limited data
Limited data
Sparse data. Doses and effects may be unreliable or untested.
- 3 corroborating sources
- no dose data
- duration data present
- 19 combo interactions documented
- classified Tentative
- classified Research-chemical
Limited data
Sparse data. Doses and effects may be unreliable or untested.
- 3 corroborating sources
- no dose data
- duration data present
- 19 combo interactions documented
- classified Tentative
- classified Research-chemical
Aliases: Fu-f, furanyl-fentanyl
Summary
Furanylfentanyl (Fu-F) is a potent ฮผ-opioid full agonist approximately 50-100 times more potent than morphine and roughly half as potent as fentanyl. U.S. and EU regulators placed it in Schedule I after at least 23 confirmed deaths in Europe alone by 2017. It exhibits rapid-onset but short-lived euphoria and profound respiratory depression.
Dose Information
Dose basis. No verified human dose exists for furanylfentanyl. A previous version of this page carried a numeric dose ladder that was wrong by roughly one to two orders of magnitude in the dangerous direction. It was removed on 7 August 2026 rather than replaced, because the defensible corrections span a 15-fold range and publishing a precise number we cannot source is the error that caused the problem. It is broadly fentanyl-equivalent in potency; our fentanyl record puts a common insufflated dose at 25-50 micrograms. Assume microgram activity, volumetric dosing only, and naloxone to hand.
Onset, Duration & After-effects
| ROA | Onset | Total |
|---|---|---|
| Oral | 1-10 min | 1-3 hrs |
Effect Profile
3 reportsScores (1–10) curated from multiple sources:
- Effect keyword matching from PsychonautWiki catalog
- Weighted by importance: core (×3), major (×2), minor (×1)
Opioid
7.0
Strong+
7/10
Strong euphoria, itching/nausea, and pain relief with low sedation
Euphoria / Warmth
×3
10
physical euphoria
cognitive euphoria
euphoria
warmth
mood lift
Analgesia
×2
8
analgesia
pain relief
Sedation / Relaxation
×1
3
sedation
Itching / Nausea
×1
10
itching
nausea
constipation
Based on reports from:
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Name
Furanylfentanyl
Unit
mg
Description
Furanylfentanyl Source: SubstanceSearch (substancesearch.com) Oral duration: onset 1-10m ยท total 1-3h ยท after-effects 1-3h Note: ranges are harm-reduction guidance, not a prescription. Start low, go slow, and test your substances.
The app keeps custom substances simple, so the full dose ranges live in the description text above. Ranges are harm-reduction guidance, not a prescription.
Tolerance
Build-up
develops within days of regular use; analgesic tolerance faster than respiratory depression tolerance
Reset
7โ14 days for partial reset; full reset may take weeks โ tolerance loss greatly increases overdose risk
Tolerance Decay
Full tolerance
7d
Half tolerance
7d
Baseline
~35d
Acute tolerance: develops within a single session โ the reset numbers above apply after sustained heavy use, not after one binge. Within-session tachyphylaxis usually resets largely overnight.
Opioid tolerance accrues rapidly with repeated use and decays over days to weeks; resuming prior doses after a break markedly increases overdose risk. Data specific to furanylfentanyl are limited; estimates are based on general opioid tolerance patterns and case observations.
Cross-Tolerances
opioids
60%
Effects
Aggregated from 3 Erowid experience reports
Positive Effects 1
Anxiety Suppression
100.0%
70%
Adverse Effects 0
Combinations
Cross-Check Furanylfentanyl with another substanceCommunity Trip Reports
Anecdotal first-person accounts from Reddit, Erowid, and Bluelight. Click a source to expand. Reports are harm-reduction context, not medical guidance. Tags summarise each author's own verdict — how reports are classified.
Erowid 3 reports 3 cautionary visit
Vaporised Fentanyl Overdose Hey folks, let me tell you the story of how I flipped my life upside down. Back in November I got out of a very toxic and abusive relationship and spiralled into a 4 month bender, abusing anything and everything I could get my hands on, which ended in a near fatal overdose.
Vaporised Fentanyl Overdose Let me tell you the story of how I flipped my life upside down. Back in November I got out of a very toxic and abusive relationship and spiralled into a 4 month bender, abusing anything and everything I could get my hands on, which ended in a near fatal overdose.
Furanylfentanyl's nerd page
Pharmacology, chemical data, effect profiles, and more
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Helpful Links
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