Introduction: The use of immunoassays for drug screening has increased due to their sensitivity towards target analytes. Due to their potential to interfere with drug screening tests and provide false findings, adulterants pose a new challenge in the detection of drug abuse. Objectives: The aim of the current study is to evaluate the effect of some adulterants on the detection of drug abuse in urine tested by immunoassay test strips and the effect of the adulterants on the validity of the results of these tests. Materials and methods: Urine samples tested positive by immunoassay test strips for one of the five abused drugs (tramadol, cannabis, morphine, benzodiazepines (BDZ), and amphetamines) were used. With help of Indiko (thermoscientific fully automated urine enzyme immunoassay), we chose two different concentrations of each drug, the first is just above the cutoff level of test strips, and the other is higher than the double cutoff. Four adulterants (vinegar, bleach, Visine eye drops, and water) were tested for their ability to generate false negative results for the chromatographic immunoassay test strips. Each adulterant was added to a urine sample containing 1 of 5 different drugs at fixed concentrations. Adulterants were also added to negative control samples to reveal how integrity criteria (pH and specific gravity (SG) were affected. Results: out of the 4 adulterants, vinegar generated the most false negatives. Bleach turned both low and high concentrations of positive cannabis samples into negative ones. Visine eye drops masked the positivity of the low-concentration cannabis sample. Water was effective in concealing the positivity of the low-concentration BDZ sample. Conclusion: A positive urine sample that includes drugs may nevertheless be examined and declared "clean and free of drugs" after passing a routine screening procedure. We recommend that drug screening tests be frequently combined with adulterant test strips to guarantee that the integrity of the specimen has not been compromised before drug testing.