30 years ago when I was a 1st Cat for a couple of years, with a full time job, I gave Creatine a go.
I definitely had a little fluid retention, but hard training sessions felt like I could push harder, and I recovered better.
I rode an 85-mile Sunday roadrace with my usual peer group, got in the break with seven other guys, pretty well bossed it and won all three Primes without even trying that hard. It felt like the race was mine for the taking, guys were telling me I was going like a train. 10 miles from the end of the race I started getting weird sensations, it was as if there was an electrical storm in my legs, gradually worsening. 300m to go, the sprint opened up, I got out of the saddle and both my legs simply locked up. I coasted across the line, last in the group, and was screaming for folks at the finish line to catch me and hold me up. They had to lie me down on my side, still clipped in, and prise me off the bike while the cramp had me crying out in pain.
I never used it again.