Zantac (ranitidine) is well known to cause false-positives for amphetamine products (e.g. Adderall, methamphetamine) on standard urinalysis drug tests.
Ranitidine Causing False Positive For Amphetamines
Urinalysis tests are the most commonly utilized drug screenings used by employers, doctors etc... Unfortunately, these tests are subject to false positives. The problem is how the urinalysis tests work. The tests (known as immunoassay tests) work by utilizing antibodies to react to a specific drug compound. When a specified drug (i.e. drug that is being tested for) is present in a urine sample, antibodies bind to it, producing a reaction which is recorded as a positive result.
One of the main issues with urine immunoassay tests is that there can be a significant problem with cross-reactivity. There are times where drugs that are not being tested for react with the wrong antibody (i.e. 'cross react'), resulting in a 'false positive'. In this case, ranitidine is cross-reacting with the antibodies that are present to detect amphetamine compounds.
The problem with cross-reactivity is a known limitation with standard immunoassay drug tests. Unfortunately, once someone has failed this initial screening, they very often don't get a chance to use a more accurate drug screening test. Ideally, for those who have a positive test using an immunoassay screening, a more specific test such as gas or liquid chromatography with mass spectrometry should be used.
If you had a false-positive for amphetamine use, be sure to let the tester or your doctor know. Hopefully you are allowed to re-test or have a more accurate screening done (e.g. with mass spectrometry). You can always reference the plethora of data available that suggests that ranitidine is a known causative agent for amphetamine (as well as methamphetamine) false-positives (Source: ScienceDirect, AACC Journal, Toxicology).