This stimulant has bee found in body building supplements according to Wikipedia:
In February 2012, the deaths of two U.S. soldiers who collapsed during physical training in the last few months have prompted a military investigation of the popular bodybuilding supplement that was found in their systems. This prompted the Department of Defense to pull products containing methylhexaneamine from on-base store shelves pending an investigation.
The drug was originally created as decongestant by Eli Lilly in 1944 but it seemingly has no medical uses whatsoever but don't let that stop the supplement people:
Patrick Arnold reintroduced methylhexanamine in 2006 as a dietary supplement,after the final ban of ephedrine as a dietary supplement in the United States in 2005. Arnold introduced it under the trademarked name Geranamine, a name held by his company, Proviant Technologies. Other supplement names which have been mentioned as containing methylhexamine include Jack3d, Oxyelite Pro, Hemo Rage Black, Dexaprine, M5 Extreme, Muscle Meds Code Red, Lipo 6 Black, 1 M.R., DynaPep, Anarchy Covalex, Muscle Spike, Noxipro, Isatori PWR, Muscletech Neurocore, Muscletech Hydroxystim, Fahrenheit Nutrition Lean EFX, Muscle Warfare Napalm, SNI Nitric Blast, BIORhythm SSIN juice, Gaspari Nutrtion Spirodex, MethylHex42, Grenade Universal Grenade, M.A.P. (iovate) Arson, or Geranamine.
So, here we have a swimmer with a 6-month ban for inadvertently ingesting a chemical by way of what: a nutritional supplement? Seems plausible!