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    Disclaimer
    ☠ This is a fentanyl analogue active in microgram doses. Accidental overdose can be rapidly fatal. Naloxone should always be on hand.
    🧪 This is a research chemical with limited data on its long-term health effects, toxicity profile, and safe dosage ranges.

    4-Fluorobutyrfentanyl

    Aliases: Pfbf, 4-fbf, parafluorobutyrfentanyl

    Depressant Research-chemical Opioid

    Summary TripSit

    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 TripSit

    ROA Light Common Strong Heavy
    Oral 300ug 600-900ug 900-1200ug 1200ug+
    Light Common Strong Heavy

    Onset, Duration & After-effects TripSit

    Effect Profile

    2 reports

    Scores (1–10) curated from multiple sources:

    • Effect keyword matching from PsychonautWiki catalog
    • Weighted by importance: core (×3), major (×2), minor (×1)

    Full methodology

    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:
    Erowid Experience Reports PsychonautWiki 4-Fluorobutyrfentanyl
    View methodology →

    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

    Effects TripSit

    Positive
    • Analgesia
    • Stimulation
    • Physical euphoria
    Negative
    • Dry Mouth
    • Increased heart rate
    • Nausea
    Neutral
    • 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
    Neutral
    • Dulled perception

    Combinations TripSit

    4-Fluorobutyrfentanyl's nerd page Pharmacology, chemical data, effect profiles, and more
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    Helpful Links

    📘 Experience Reports 📖 TripSit 📖 PsychonautWiki