Hello. Welcome to Ask The Doctor. I understand your concern.
Zantac is Ranitidine which is a H2 blocker and yes, and it can cause false positive test for methamphetamine. Other drugs which are known to cause false positive tests are bupropion, chlorpromazine, clomipramine, dextromethorphan, diphenhydramine, and ibuprofen.
However a single dose of Zantac is unlikely to cause false positive test but yes, chronic use can.
Share my opinion with your doctor.
I hope it helps.
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