I don't know that 2.5 is recommended, but it was the "most effective". You can get 90% of the DHT blockage with .5mg, which is what most people here take.
Recommended by whom? :dunno: There's no doubt whatsoever in my mind that if it were actually approved by the FDA to treat male pattern baldness (not likely ever to happen), it would be approved at the same dose as it's currently used for BPH (0.5 mg/day), or maybe even a bit lower.