Procyanidin B2

What it is

Procyanidin B2 is a dimer of the flavan-3-ol catechin found in apples, barley and cocoa. Topical tonics in trials used 1%, and an Italian oral supplement used Annurca apple extract.

How it works

In cultured mouse hair epithelial cells, procyanidin B2 neutralized growth inhibition and cell death caused by TGF-beta1 and TGF-beta2 and raised MEK-1/2 expression (Kamimura 2006). TGF-beta drives catagen, so the idea is delaying regression. Annurca extract raised keratin expression in a human skin model (Tenore 2018).

What the studies show

• In 29 men (19 active, 10 placebo), a 1% tonic for 6 months raised total hairs by 6.68 versus 0.08 per 0.25 cm² (p<0.005) and terminal hairs by 1.99 versus a fall of 0.82 (p<0.02). Kamimura 2000
• A 4-month trial, also 19 versus 10 men, raised total hairs by 3.67 versus a fall of 2.54 (p<0.001), and 78.9% versus 30% had thicker mean hair. Takahashi 2001
• An oral Annurca apple extract trial reported more hair growth, density and keratin expression at 2 months, with no competing interests declared. Tenore 2018
• A systematic review of 30 supplement studies put the apple nutraceutical among the supplements with higher-quality evidence, with rare and mild adverse effects. Drake 2023

The two Japanese papers have identical group sizes and overlapping authors, so they are probably one cohort and are best treated as a single trial. The authors worked at the company that makes the extract, and the abstracts report only mean counts in a 0.25 cm² window.

How it's used in studies

A 1% procyanidin B2 tonic for 4-6 months. The oral Annurca extract dose was not stated in the abstract.

Side effects and safety

No adverse effects were reported in the 29-man trials. Apple polyphenols are food compounds and no serious concerns are known.

Bottom line

Limited evidence: small, industry-linked human trials with tiny absolute gains of a few hairs per 0.25 cm². It is low risk, but do not expect meaningful regrowth.