The Basics of Drug Testing: Screening vs. Confirmation
Before diving into specific medications, it is important to understand the two main types of drug tests used. The process typically starts with a rapid, low-cost screening test, most often a urine immunoassay. These screens are designed to detect the presence of common drug classes (e.g., opioids, amphetamines, benzodiazepines) quickly. However, they can sometimes cross-react with other substances, including legally prescribed medications, because of similar chemical structures. This can lead to an inaccurate 'non-negative' or 'presumptive positive' result, also known as a false positive.
If a screening test is non-negative, a more advanced and specific test is performed to confirm the result. This confirmatory testing uses highly accurate laboratory techniques, such as Gas Chromatography-Mass Spectrometry (GC-MS) or Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS). These methods can precisely identify the specific drugs and metabolites present in the sample, effectively distinguishing between a prescribed medication and an illicit substance.
How Seizure Medications Can Affect a Drug Test
Many seizure medications (also known as anticonvulsants or antiepileptic drugs) do not typically show up on standard drug panels, which screen for illicit substances. For example, gabapentin is not usually tested for unless a specialized test is ordered, often due to concerns of misuse. However, some seizure medications can cause interference during the initial screening phase, leading to false-positive results.
Medications That Can Cause False Positives
- Lamotrigine (Lamictal®): Case reports have documented that lamotrigine can produce a false positive result for phencyclidine (PCP) on certain rapid urine toxicology screens. A confirmatory test is essential to resolve this issue.
- Carbamazepine (Tegretol®): Reports have noted that carbamazepine can cause false-positive results on urine drug screens. It has been shown to potentially interfere with tricyclic antidepressant (TCA) screens due to its chemical structure.
- Carvedilol: Though not a seizure medication, it has been linked to false-positive PCP screens in some cases. This highlights how drug structure similarities can create unexpected cross-reactivity issues.
- Benzodiazepines: Some seizure medicines, like clonazepam (Klonopin®), are benzodiazepines and will be detected on a standard drug test that screens for this class. If you have a valid prescription, this is not an issue, but it must be disclosed.
Medications That Can Be Directly Detected
Some seizure medications, particularly certain benzodiazepines, are specifically monitored. Clonazepam, for instance, is a benzodiazepine that can be detected on standard drug panels. The key difference here is that a prescription for these medications is a valid reason for a positive test. However, you must inform the testing facility of your prescription to avoid complications. Another example is Vimpat, a controlled substance that can be prescribed for seizures. While it is a specific drug, the fact that it is a controlled substance means a test for it could be requested in certain scenarios.
Comparison Table: Common Seizure Meds and Drug Test Interference
| Seizure Medication | Potential for False Positive (FP) | Detection on Standard Drug Panel | Action to Take for a Drug Test |
|---|---|---|---|
| Lamotrigine (Lamictal®) | Yes (for PCP, Immunoassay) | No (unless specialized test) | Inform tester of prescription; confirmatory test will clear. |
| Gabapentin (Neurontin®) | Very low risk | No (unless specifically requested) | Inform tester if tested for misuse; typically not an issue. |
| Carbamazepine (Tegretol®) | Yes (potential for TCA screen) | No (unless specialized test) | Disclose prescription; confirmation needed if a screen is positive. |
| Clonazepam (Klonopin®) | No (is a benzodiazepine) | Yes (Benzodiazepine Panel) | Present valid prescription; the positive result is expected and justified. |
| Levetiracetam (Keppra®) | Not known to cause FPs | No (unless specific clinical test) | Should not cause interference on standard tests. |
| Phenytoin (Dilantin®) | Low risk | No (unless specific clinical test) | Inform tester of prescription; monitored via clinical blood tests. |
Factors Influencing Detection Times
The length of time a medication is detectable in the body depends on several factors, including metabolism, kidney function, and the dosage. Gabapentin, for instance, has a relatively short half-life of 5-7 hours, but for someone with impaired kidney function, it could remain in the system much longer. Hair follicle tests have the longest detection window—up to 90 days for certain substances—while blood tests typically have the shortest. The type of test used for screening will also determine the likelihood of detection. Because of these variables, it is always recommended to be transparent with testing personnel if you are prescribed any medication.
What to Do Before a Drug Test
If you are taking a seizure medication and must undergo a drug test, taking a proactive approach can prevent confusion and protect you from false accusations. The first step is to be transparent with the testing facility. Inform the staff that you have a prescription for a seizure medication, providing the name of the drug. It is also wise to have proof of your prescription available, such as a bottle with the label or a note from your doctor. This is especially important for medications like clonazepam, which are controlled substances and will trigger a positive result for benzodiazepines. Knowing that false positives on initial screens are a possibility, you can address any presumptive positive results calmly, knowing that a confirmatory test will provide an accurate outcome. An employer, for example, will not receive your specific medical information but will be informed of a verified, legitimate medical reason for a test result.
Conclusion
While many seizure medicines do not appear on standard drug tests, the possibility of a false positive on an initial immunoassay screening exists for certain drugs like lamotrigine. Medications that are controlled substances, such as some benzodiazepines, will trigger a positive result that can be justified with a valid prescription. The key to navigating this situation is transparency and understanding the difference between initial screens and highly accurate confirmatory tests. By informing testing personnel of your medication and having documentation ready, you can ensure your test results are interpreted correctly and avoid potential misinterpretations. For more information, the Epilepsy Foundation offers resources and community support.
