It could have just been a coincidence, but my thinning actually started right after starting creatine.
I was deployed to Afghanistan and became obsessed with fitness while over there, was working out every day, morning and night. I used creatine, protein, and nitric oxide.
Prior to this my hair was pretty good. After I came back to the states I cycled off and shortly after noticed slight thinning. I was 25 at the time.
I was back stateside for about 4 months before deploying again. During that trip everyone pointed out that my hair was thinning at a really fast rate. I only worked out 5 days a week since it wasn't as dangerous of a deployment compared to the previous and I was still jacked. I didn't even use any supplements.
When I got back I was 26 and my diffuse thinning was an issue.
Side note: Around that time I also had the anthrax shot and 3 boosters (1 extra due to a med f*** up), and that is known to also cause all kinds of problems.