The Costa brothers say their positives were the result of a supplement. It is possible--check out this article about the methylhexanamine positives at the Commonwealth Games:
also:CWF chief Fennell said: "We are concerned with the number of incidents that are coming up with the same substance.
"At this stage I cannot speak very definitively as to where it's coming from but it appears that it may be coming from the use of supplements."
The drug, which has some performance-enhancing qualities, is commonly found but often not labelled in supplements and products such as nasal decongestants.
As the BBC's Steve Cram notes, the drug can therefore be taken by accident