Background: Me: Female, 24yo, 30+ substances used in the past. Previous use of PFBF up to 4mg iv. Use of PFBF started a few weeks prior when we obtained the substance. 6 years of drug use. My Husband: Male, 26yo, 50+ substances used in the past. Previous use of PFBF up to 5mg iv. 10 years of drug use.
4-Fluorobutyrfentanyl
Encyclopedic
Encyclopedic
Typical encyclopedia coverage. Cross-reference for important decisions.
- 2 corroborating sources
- 1 ROA with full dose ladder
- duration data present
- 29 combo interactions documented
- classified Research-chemical
Encyclopedic
Typical encyclopedia coverage. Cross-reference for important decisions.
- 2 corroborating sources
- 1 ROA with full dose ladder
- duration data present
- 29 combo interactions documented
- classified Research-chemical
Aliases: Pfbf, 4-fbf, parafluorobutyrfentanyl
Summary
Rare, little known and extremely potent RC analogue of Fentanyl. This powerful opioid is generally only dispensed as a nasal spray. Handle with extreme caution and never mix with other depressants.
Dose Information
| ROA | Light | Common | Strong | Heavy |
|---|---|---|---|---|
| Oral | 300ug | 600-900ug | 900-1200ug | 1200ug+ |
Light
Common
Strong
Heavy
Sources
Oral
Dose ladder — TripSitOnset, Duration & After-effects
| ROA | Peak | Total |
|---|---|---|
| Oral | 30-60 min | 30-60 min |
Effect Profile
2 reportsScores (0–10) curated from multiple sources:
- Effect keyword matching from PsychonautWiki catalog
- Weighted by importance: core (×3), major (×2), minor (×1)
Opioid
6.3
Strong
6/10
Strong euphoria with moderate itching/nausea, mild pain relief, low sedation
Euphoria / Warmth
×3
10
physical euphoria
euphoria
cognitive euphoria
mood lift
Analgesia
×2
4
analgesia
Sedation / Relaxation
×1
3
sedation
Itching / Nausea
×1
7
nausea
constipation
dry mouth
Based on reports from:
Tolerance
Build-up
develops within days of regular use; analgesic tolerance faster than respiratory depression tolerance
Reset
Falls quickly once you stop, at a rate you can't judge. After any break, treat your tolerance as gone.
No tolerance chart. Our decay curves for opioids were estimates, and a curve can make tolerance look longer-lasting than it is, which is the dangerous direction.
Opioid tolerance drops fast when you stop, and even a few days off can be enough, so a dose that used to be normal can now stop your breathing. Overdose deaths rise sharply after prison, detox or leaving treatment, and tolerance also falls during a hospital stay. After any break, start with a much smaller amount, try a test dose first, don't use alone, and keep naloxone within reach. Alcohol, benzodiazepines, gabapentinoids and other sedatives make an opioid overdose much more likely.
Sources: FRANK: heroin · National Harm Reduction Coalition · WHO: opioid overdose · Merrall et al. 2010 · Binswanger et al. 2007 · Strang et al. 2003 · FDA 2019: gabapentinoids and breathing
Effects
Effect glossary — · full glossary
Positive
Negative
Positive
Negative
Positive
Negative
Combinations
Cross-Check 4-Fluorobutyrfentanyl with another substanceCommunity Trip Reports
Anecdotal first-person accounts from Reddit, Erowid, Bluelight, and Dose.wiki. 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 2 reports 2 cautionary visit
I wrote the report during the first test, while I was at home just chilling and typing this up, before I flopped on my bed at the tail end of the experience. I was being careful (take into account that I do have tolerance) but on the other occasions I dosed higher I did not write timed reports (I was too busy enjoying...
4-Fluorobutyrfentanyl's nerd page
Pharmacology, chemical data, effect profiles, and more
→
Helpful Links
Add to PsychonautWiki Journal
The PsychonautWiki Journal logging app doesn't include every substance. To track 4-Fluorobutyrfentanyl there, start adding an ingestion, search for the name, and choose to add it as a custom substance. Paste these values:
⬇ Download import file
Import this file as custom substances
and you get "4-Fluorobutyrfentanyl (Substance Search)" with every
route's full dose ladder and timeline, no typing. Works on iOS and
Android (v15+); the format is confirmed by the app's
developer. The manual values below work for older
versions.
Name
4-Fluorobutyrfentanyl
Unit
µg
Description
4-Fluorobutyrfentanyl Source: SubstanceSearch (substancesearch.com) Oral dose (µg): light 300ug · common 600-900ug · strong 900-1200ug · heavy 1200ug+ Oral duration: peak 0.5-1h · total 0.5-1h Note: ranges are harm-reduction guidance, not a prescription. Start low, go slow, and test your substances.
Tip: for quicker logging you can also add a Custom Unit in the app, e.g. common dose ~ 750 µg (Oral).
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.
Report an issue or suggest an edit
Spotted incorrect or dangerous information, have a correction, a new study, or a useful addition for 4-Fluorobutyrfentanyl? Let us know. Reports are reviewed by moderators — this is not posted publicly.