text: if you never used crystal meth how can it show up in your blood?   it depends on the test used, but many chemicals will show up as methamphetamine. ephedra (weight loss drug that is now illegal but it's in some plants and i'm sure people can still get it), pseudoephedrine(in sudafed and many cough medicines), any kind of amphetamine (such as in a prescription weight loss or adhd drug like desoxyn, dexadrine, adderall). i've heard of kidney disease and diabetes causing false positives. also you don't have to be using crystal meth do be using methamphetamine, there are also powdered forms, and pills, and a lot of low grade mexican cocaine contains small amounts of methamphetamine that boost the cocaine high without the user knowing it's there. you can tell by tasting the coke, if it takes a second or two before it gets the bitter coke taste and during that time there's a bland taste you just can't figure out, it's mostly likely cut with it.