How to Challenge a Positive Drug Test in a Criminal Case
Introduction
In many drug-related criminal cases, a positive drug test is treated as powerful evidence by the prosecution. However, drug tests are not infallible. False positives, lab errors, and violations of testing procedures can all result in inaccurate or misleading results. If you’ve been charged or violated probation based on a positive test, you have the right to challenge its validity.
This article explains how drug testing works in California criminal cases, common flaws in testing, and the legal strategies your defense attorney can use to dispute questionable results.
Types of Drug Tests Used in Criminal Cases
Depending on the circumstances, the court may rely on different drug testing methods, each with its own advantages and limitations:
- Urine testing – most commonly used, but highly susceptible to contamination and false positives
- Hair follicle testing – detects long-term drug use but does not show recent activity
- Blood testing – more accurate but less commonly used due to invasiveness and cost
- Saliva testing – used in some roadside stops but often challenged for accuracy
Each method must follow strict collection, storage, and chain-of-custody protocols to ensure reliability. Any deviation may give your attorney grounds to suppress the results.
Common Defenses Against Positive Drug Tests
There are several ways to legally challenge a drug test in a criminal case. Your defense strategy may include:
- Lab errors or mishandling of samples
- Contaminated equipment or poor testing conditions
- False positives from legal substances (e.g., poppy seeds, cold medications)
- Lack of confirmatory testing (such as a second, independent test)
An experienced attorney can subpoena lab records, cross-examine technicians, and consult toxicologists to dispute unreliable drug test results—potentially weakening or dismissing the prosecution’s case.
