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
- 19 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
- 19 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
Onset, Duration & After-effects
| ROA | Peak | Total |
|---|---|---|
| Oral | 30-60 min | 30-60 min |
Effect Profile
2 reportsScores (1–10) 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
7–14 days for partial reset; full reset may take weeks — tolerance loss greatly increases overdose risk
Tolerance Decay
Full tolerance
1d
Half tolerance
21d
Baseline
~35d
Acute tolerance: develops within a single session — the reset numbers above apply after sustained heavy use, not after one binge. Within-session tachyphylaxis usually resets largely overnight.
Effects
Positive
- Analgesia
- Stimulation
- Physical euphoria
Negative
- Dry Mouth
- Increased heart rate
- Nausea
- Itchiness
- Relaxant
- Pupil constriction
- Sedation
Positive
- Euphoria
- Mood lift
- Reduced anxiety
- Cognitive euphoria
- Anxiety suppression
Negative
- Constipation
- Compulsive redosing
- Anxiety
- Thought deceleration
- Amnesia
Positive
- Increased music appreciation
- Increased libido
- Tactile enhancement
- Color enhancement
Negative
- Disinhibition
- Light sensitivity
- Appetite suppression
- Dehydration
- Double vision
- Dulled perception
Combinations
Cross-Check 4-Fluorobutyrfentanyl 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.
Erowid 2 reports 2 neutral 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
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Helpful Links
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