"We are certain that this did not constitute a stimulant effect, but I do understand that there will be repercussions for this misjudgment," continued O'Neill. "I sincerely apologise to my Health Net team, my sponsors and my fans for this embarrassing situation."
yeah ... he was pretty sure there would be no "stimulant effect" from taking a diet drug before a 4.5km time trial.
and i'm sure he's a great guy.
Phentermine, like many other prescription drugs, works with neurotransmitters in the brain. It is a centrally-acting stimulant and is a constitutional isomer (not to be confused with stereoisomer) of methamphetamine. It stimulates neuron bundles to release a particular group of neurotransmitters known as catecholamines; these include dopamine, epinephrine (also known as adrenalin), and norepinephrine (noradrenaline).
... performance enhancer.