Perhaps you should try some spelling variations:
"performance-enhanced drugs" » "performance-enhanced drug", "performance-enhance drug", "performance-enhanced drought"
"performance-enhancing drug" » "performance-enhancing drugs", "performance-enhanced drug", "performance-enhancing design"
"performance-enhancing data" » "performance-enhancing a"

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (("performance-enhanced drugs") OR ((("performance-enhancing drug") OR ("performance-enhancing data")))).
• Removing quotes may allow a broader search: (( performance-enhanced drugs ) or ((( performance-enhancing drug ) or ( performance-enhancing data )))).
• Adding a wildcard symbol may retrieve word variants: (("performance-enhanced drugs") or ((("performance-enhancing drug") or ("performance-enhancing data"))))*.