4F-piHP

4-Fluoro-α-pyrrolidinoisohexanophenone (4F-PiHP) is a synthetic cathinone in the pyrrolidinophenone subgroup. It is a fluorinated analogue of α-PiHP, with a fluorine atom at the para position of the phenyl ring. The compound belongs to a group of newer α-PiHP derivatives that have appeared as stimulant replacements. Recent laboratory research has found strong activity at dopamine and norepinephrine transporters, but there are no controlled human studies establishing its effects or safety.

Chemistry

4F-PiHP contains the β-keto amphetamine framework characteristic of cathinones, together with a pyrrolidine ring attached to the alpha carbon. Its fluorine substituent is located at the para position of the phenyl ring. It is closely related to α-PiHP and to other fluorinated pyrrolidinophenones.

The name is sometimes written as 4-F-α-PiHP or 4-fluoro-α-PHP. It should not be confused with 4F-PHP when that abbreviation is used for a compound with a different side-chain length or naming convention; chemical identity should be checked against the full structure.

Pharmacology

A 2026 study examined α-PiHP and five related analogues, including 4-F-α-PiHP. The researchers measured activity at human dopamine, norepinephrine and serotonin transporters, and also tested behavioural effects in mice. All of the compounds strongly inhibited dopamine and norepinephrine uptake while showing limited activity at the serotonin transporter. The results were consistent with a stimulant profile and high reinforcing potential in the animal models (Pazos and colleagues, 2026).

The study found that the position of the ring substituent mattered: meta-substituted analogues generally showed stronger dopamine-transporter affinity and behavioural effects than their para-substituted counterparts. The paper therefore provides compound-specific evidence for 4-F-α-PiHP, while also showing that it should not be assumed to behave identically to α-PiHP or the 3-fluoro isomer.

Reported effects

Verified human accounts are too limited to establish a characteristic 4F-PiHP experience. Its stimulant profile is supported by laboratory and animal findings, but claims about euphoria, focus, sociability or the duration of effects would rely mainly on anecdotal reports.

Behavioural findings and toxicity

In the 2026 study, the α-PiHP analogues produced psychostimulant and rewarding effects in mice. The researchers also assessed lethality, but the strongest evidence of lethality was associated with MDPiHP rather than specifically with 4-F-α-PiHP. The findings raise toxicological concerns about this group of analogues, without establishing the toxicity of 4F-PiHP in humans.

There are no established human data on its metabolism, acute toxic range, dependence potential or long-term effects. As a potent dopamine- and norepinephrine-transporter inhibitor in vitro, it raises concerns associated with stimulant exposure, but the severity and frequency of adverse effects in people remain unknown.

Related compounds

4F-PiHP is related to α-PiHP, 4F-PHP and other pyrrolidinophenone cathinones. Its para-fluoro substitution distinguishes it from the parent compound and from the corresponding meta-fluoro analogue.