Creatine falls into the category of potentially useful chemicals easily found in animal products but not in plant products (similar to b12) & I've seen a plant-based doctor recommend it in certain cases.
Wikipedia has a non-answer that just asserts the supplement form is not animal-derived, but doesn't say what it is.
Reference: https://www.maximuscle.com/nutrition/ingredients/creatine/How-Is-Creatine-Made/
How is creatine manufactured synthetically?
Creatine monohydrate supplements are manufactured outside the body from sarcosine and cyanamide. They are generally combined in a reactor with other catalyst compounds.
Once in the reactor, it’s heated and pressurised to form creatine crystals. At this point, any unwanted particles will be removed by centrifuge before being vacuum dried. It is usually milled into a fine powder to improve dissolvability.
Sarcosine may not be vegan, though.
Reference: https://doublecheckvegan.com/ingredients/sarcosine/
Sarcosine may or may not be vegan. It is an Amino Acid, used in cosmetics as a skin conditioner. Sarcosine can be obtained from parts of slaughtered animals or from plants or microbiological sources.
Reference: https://vegfaqs.com/are-creatine-supplements-vegan-friendly/
Creatine can be made in a lab or extracted from animals.
The same reference claims some manufacturers certify their creatine monohydrate powders as vegan. So, the brand would matter.
