Certain prescription medications produce metabolites that appear in drug testing results in ways that resemble controlled substances. When a service member tests positive and has a legitimate prescription that could explain the result, the prescription defense becomes available, but it is not automatic and it is not simple to establish. The confirmatory testing process used by military laboratories is designed to distinguish between compounds, but there are documented cases where prescribed medications have created results that required expert analysis to properly interpret.
Establishing a prescription defense requires documentation of the prescription, timing evidence that connects the medication to the period of the positive test, and in many cases expert testimony from a pharmacologist or toxicologist who can explain the scientific basis for the result. The government will challenge every element of this defense, and the service member must be prepared to respond. Building this case before any hearing begins is far more effective than assembling it under pressure after proceedings have started.
Common Prescription Medications That Trigger False Positives
Certain legally prescribed medications are known to produce immunoassay screening results that resemble controlled substances because of metabolic similarities between the prescribed compound and the tested substance. Amphetamines and methamphetamine are among the most common cross-reactive categories, with prescription medications including certain decongestants, ADHD treatments, and specific antihistamines documented to produce positive screening results in standard immunoassay panels.
Opioids present a similar dynamic. Codeine, hydrocodone, and other prescription opioids are metabolized in ways that can appear on a standard screen as heroin metabolites. Benzodiazepine cross-reactivity has been documented with certain muscle relaxants and sleep aids. The military’s testing program uses confirmatory GC-MS or LC-MS analysis specifically because the screening step is known to produce these results, and the confirmatory step is designed to distinguish between the prescribed substance and the targeted controlled substance. However, the confirmatory process has its own documented limitations, and the distinction between prescription metabolites and illicit substance metabolites is not always perfectly resolved.
The Confirmatory Testing Process and Its Reliability
Military drug testing uses a two-step process: an initial immunoassay screening that identifies specimens presumed positive and a confirmatory gas chromatography-mass spectrometry test that identifies the specific substance and its metabolite concentration. A charge can only be based on a confirmed positive from the GC-MS test. The immunoassay result alone is not evidence of an offense. The GC-MS confirmation is the legally operative finding.
The GC-MS process is considered highly specific and reliable for identifying the target analytes when the specimen is properly maintained and the analysis is correctly performed. But the confirmatory test does not identify the source of the substance. It confirms the presence of a metabolite at or above the reportable threshold. A prescription defense does not challenge the accuracy of the test result. It accepts the result and argues that the presence of the metabolite is explained by legitimate medical use.
How to Document a Prescription Defense Before the Proceedings Begin
A prescription defense requires contemporaneous documentation that existed before the positive test was reported. The most important documents are the prescription itself, showing the prescribed substance and the prescribing provider, and any records of the dispensing pharmacy showing that the prescription was filled and the dates of fills that correspond to the period of alleged use. A prescription that was written after the positive result was reported, or that was backdated, will not support the defense and will create additional credibility problems.
Medical records from the treating provider documenting the diagnosis, the treatment rationale, and the prescription are additional supporting documentation. In cases where the prescribed medication contains a substance that is a scheduled controlled substance under the UCMJ framework, the defense must also show that the medication was taken within the prescribed dosage and that the metabolite level in the reported result is consistent with therapeutic use of the prescribed amount. A forensic toxicologist can perform this analysis if the relevant records are available.
What the Government Must Prove When a Prescription Is Raised
When a prescription defense is raised, the government cannot simply rest on the confirmed positive result. It must either prove that the service member did not have a valid prescription covering the period of alleged use, prove that the service member exceeded the prescribed dosage in a way that violated the prescription’s terms, or establish that the substance found was not the prescribed substance but rather an additional controlled substance not covered by any prescription.
Prosecutors will conduct a thorough investigation of the prescription claim before trial, verifying the prescription’s validity through the prescribing provider and pharmacy, checking whether the medical records support the diagnosis that prompted the prescription, and in some cases retaining their own expert to evaluate whether the reported metabolite level is consistent with prescribed use. The defense must anticipate this investigation and ensure that the documentation supporting the prescription is complete and internally consistent before the government completes its review.
Limitations on the Prescription Defense in Military Courts
The prescription defense has specific limitations that service members and their counsel must understand before relying on it. It applies only when the substance found in the test is a legally prescribed medication and only when the use was consistent with the terms of the prescription. It does not apply when the service member exceeded the prescribed dosage, when they used a prescription belonging to someone else, or when the prescription was for a substance that is not subject to the UCMJ prohibition in the form in which it was prescribed.
Additionally, some commands have specific policies requiring service members to disclose controlled substance prescriptions to their chain of command or medical personnel. A service member who failed to disclose a prescription in accordance with applicable policy may face a separate accountability issue even if the prescription defense eliminates the drug use charge. Defense counsel must assess both the availability of the defense and any secondary exposure the prescription history creates before advising the client about how to proceed.
This content is provided for educational purposes only and does not constitute legal advice. Military law is complex and fact-specific. If you are facing a UCMJ investigation, court-martial, administrative separation, or any other military legal matter, consult a qualified military defense attorney before taking any action.