How Long Will Zantac Show Up In a Urine Test?

Zantac (ranitidine) is well documented as providing a false positive result for amphetamines in urine drug screens.
If you have taken Zantac legitimately (on a doctors prescription) tell the drug testing personnel.

The half-life of Zantac is about 3 hours. This is the time it takes for the drug level in your plasma to be reduced by half. So half of the Zantac is out of your system in 3 hours, leaving half. Half of the remaining half is out in the next 3 hours leaving 1/4. Half of the remaining 1/4 is out in the next 3 hours leaving 1/8, etc.
As a estimate it usually takes around 5.5 half lives for a drug to be eliminated from your system. So 5.5 x 3 = 16.5 hours. The rate of elimination of a medication varies from person to person depending on factors including age, weight, kidney function and other medical conditions the person may have.
To be safe allow 24 hours for Zantac to be out of your system.