Try asking your GP or chekcing out your closes university hospital like Queens Medical Centre in Nottingham, I remember living there as a student and they were always after volunteers for one thing or another. For something popular as hair loss treatment I would guess there is a long line of hopeful volunteers. Good Luck and don't forget to read the small print.
I'm not sure, one of my mates has made a pretty good living from having stuff tested on him. Have a look in your local student union - they normally advertise in there. I just hope that afterwards you don't get all big and green when you get angry.