community Optimal topical (leave in, not shampoo) caffeine concentration. Contradictions across studies.
One study suggests a 0.2% caffeine concentration is nearly as effective as 5% minoxidil for hair loss, while other findings indicate that concentrations between 0.001% and 0.005% are more effective, with 0.001% being the most effective. There is no clear consensus on the optimal caffeine concentration for hair loss treatment.