What would make someone test positive for amphetamines if they havent taken anyt!

What would make someone test positive for amphetamines if they havent taken anything? (serious answers only)?

My sister tested positive but she hasnt taken anything. Not even a tylenol.
Is there any thing other then "drugs" that will cause it. Thanks

"Amphetamines - Substances or Conditions which can cause false positives"

Ephedrine, pseudoephedrine, propylephedrine, phenylephrine, or desoxyephedrine
(Nyquil, Contact, Sudafed, Allerest, Tavist-D, Dimetapp, etc)
Phenegan-D, Robitussin Cold and Flu, Vicks Nyquil
Over-the-counter diet aids with phenylpropanolamine (Dexatrim, Accutrim)
Over-the-counter nasal sprays (Vicks inhaler, Afrin)
Asthma medications (Marax, Bronkaid tablets, Primatine Tablets)
Prescription medications (Amfepramone, Cathne, Etafediabe, Morazone,phendimetrazine, phenmetrazine, benzphetamine, fenfluramine, dexfenfluramine,dexdenfluramin... mephentermine, Mesocarb, methoxyphenamine, phentermine,amineptine, Pholedrine, hydroymethamphetamine, Dexedrine, amifepramone, clobenzorex,fenproyorex, mefenorex, fenelylline, Didrex, dextroamphetamine, methphenidate, Ritalin,pemoline, Cylert, selegiline, Deprenyl, Eldepryl, Famprofazone) Kidney infection, kidney disease, Liver disease, diabetes"

http://www.passyourdrugtest.com/false-po...

Also:

http://p072.ezboard.com/fmethmadnessfrm1...