Screening immunoassays are presumptive. A non-negative screen is not a positive result until it is confirmed by GC-MS or LC-MS/MS. Below are the substances with documented cross-reactivity or false-positive reports, each linked to its full reference page. If you have a legitimate prescription, declare it through the Medical Review Officer (MRO).
By substance
Adderall / amphetamines
- Documented amphetamine-screen cross-reactants include bupropion (Wellbutrin), labetalol, phentermine, pseudoephedrine/Sudafed, methylphenidate (some assays), trazodone, selegiline, and promethazine — immunoassay positives only; GC–MS confirmation distinguishes them.
- Phentermine is a genuine amphetamine-class result on many assays rather than a false one — disclose it.
Alcohol
- Non-alcoholic beers, red-wine vinegar dressings, vanilla extract, some mouthwashes and cough syrups contain measurable alcohol and have triggered low-level EtG positives near cutoff.
- Hand-sanitizer absorption and bakery products have been documented near-cutoff EtG artifacts; confirmatory EtS testing and cutoff selection mitigate this.
Anabolic steroids
- Epitestosterone manipulations and designer steroids evade ratio screens; GC–C-IRMS isotope testing adjudicates elite sport cases.
Benadryl / NyQuil (diphenhydramine & doxylamine)
- PCP-screen FP (diphenhydramine, doxylamine, DXM); opiate-screen FP; methadone-screen FP; TCA-screen FP.
Benzodiazepines (Xanax, Valium, Klonopin, Ativan)
- Sertraline (Zoloft) and oxaprozin have documented case-report false positives for benzodiazepine immunoassays.
CBD (cannabidiol)
- Mislabeled CBD products containing undeclared THC cause genuine THC positives — these are true positives for THC, not assay errors.
- Pure CBD has no documented cross-reactivity with THC immunoassays.
Cocaine
- Topical cocaine solution used in ENT surgery (legitimate medical exposure) can cause a true positive — declare via MRO.
- Amoxicillin-based false positives are an urban legend for modern assays; confirmation eliminates legacy concerns.
DXM (dextromethorphan)
- High-dose dextromethorphan is a documented cross-reactant on some PCP and opioid screens — confirmation resolves it.
Delta-8 THC
- Delta-8 itself produces a genuine positive, not a false one; no OTC medication is proven to cause a confirmed THC positive.
Fentanyl
- No routine medication cross-reacts at the 1 ng/mL specialty cutoffs.
Fluoxetine (Prozac)
- Rare amphetamine-screen cross-reactivity case reports.
Hemp
- Hemp-seed products containing trace THC can produce genuine (not false) positives at high intake — declare the product through the Medical Review Officer.
Hydrocodone (Norco, Vicodin)
- Poppy-seed morphine does not create hydrocodone positives; the strips are specific.
Hydroxyzine (Atarax/Vistaril)
- TCA-screen cross-reactivity (assay-dependent).
Ketamine
- Weak PCP-screen cross-reactivity documented at screen tier.
Kratom (mitragynine)
- Kratom does not cross-react with standard opiate screens in validated assays; older studies suggested weak methadone-assay interference, resolved by confirmatory testing.
LSD (acid)
- Historic screen-level cross-reactivity with psilocin and some SSRIs on research immunoassays; irrelevant to standard panels.
MDMA (ecstasy/molly)
- High-dose fluoxetine or other amphetamine-cross-reactive drugs may flag the amphetamine portion of the assay; confirmation distinguishes true MDMA.
Methadone
- Diphenhydramine (Benadryl), doxylamine, verapamil, clomipramine, and quetiapine (Seroquel) have documented methadone-screen false positives.
Methamphetamine
- Vicks inhaler (levmetamfetamine) misuse per label instructions does not reach confirmatory levels; abuse of nasal inhalers can.
- Bupropion and trazodone can falsely flag methamphetamine SCREENS on some immunoassays — confirmation resolves.
Methylphenidate
- Amphetamine-screen interference: assay-dependent, dose-dependent; confirmation definitive.
Morphine
- Poppy-seed true positives (dietary); cutoffs calibrated for it.
Muscle relaxers (Flexeril, Soma, tizanidine)
- Cyclobenzaprine → TCA-screen FP: documented. Quetiapine/hydroxyzine share TCA-strip risk.
Nicotine (smoking/vaping/Zyn)
- No significant false positives; the assay is specific to nicotine-family compounds.
NyQuil & cold medicines
- PCP-screen FP via doxylamine/DXM (classic Mayo-table entries).
Opiates / opioids (heroin, morphine, codeine)
- Poppy seeds: documented true morphine/codeine positives; EU-source rolls are worst. Cutoff raise to 2,000 ng/mL (2000 confirm) mitigates.
- Quinine, dextromethorphan, diphenhydramine, ofloxacin/levofloxacin, rifampin: historical screen-only false positives, resolved by confirmation.
Opium
- Poppy-seed foods can contain trace morphine and codeine; the 2,000 ng/mL cutoff is set high enough that ordinary consumption rarely produces a confirmed positive, and the MRO process handles documented dietary exposure.
Oxycodone (Percocet, OxyContin)
- No significant oxycodone false positives documented on modern assays; poppy seeds affect morphine/codeine results, not oxycodone strips.
PCP (angel dust)
- Dextromethorphan (Robitussin), diphenhydramine (Benadryl), doxylamine (NyQuil), tramadol, venlafaxine (Effexor), imipramine, ketamine, and meperidine have documented PCP-screen false positives — GC–MS confirmation is definitive.
Phentermine (Adipex-P)
- Technically 'true class positive': confirmation distinguishes phentermine from amphetamine/methamphetamine; MRO reporting depends on program rules.
Psilocybin mushrooms ('shrooms')
- LSD-type immunoassays may cross-react with psilocin in theory, but neither drug is on standard panels, so this matters only in specialized orders.
Quetiapine (Seroquel)
- Methadone-screen FP (multiple published cases); TCA-screen FP (assay-dependent).
Sertraline (Zoloft)
- Benzodiazepine-screen FP case reports (sertraline).
Suboxone (buprenorphine)
- No common medication produces buprenorphine false positives; the dedicated assay is highly specific.
Sudafed (pseudoephedrine)
- Amphetamine-screen cross-reactivity documented (dose/assay dependent).
Tramadol (Ultram)
- Historic screen-level cross-reactivity with PCP and amphetamine immunoassays is documented; confirmations resolve.
Trazodone
- Amphetamine-screen false positives: case-documented (Francisco & Mehta; Roberge reports).
Weed / THC (cannabis)
- No over-the-counter medication is proven to cause a confirmed THC positive.
- Older immunoassays occasionally reacted with ibuprofen or naproxen; modern assays have largely corrected this, and GC–MS confirmation resolves it.
- Dronabinol (prescription Marinol) and hemp-seed products containing trace THC can produce genuine positives — declare your prescription through the Medical Review Officer.
Wellbutrin (bupropion)
- Amphetamine-screen false positive: extensively documented (Casey et al. 2013; Brahm 2008).