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False Positives Forum

This forum is intended to help those who Do NOT Abuse Drugs. We do NOT support the illegal use of any substance. If you have experience with false positives, share your experience. What would you tell someone about drug testing and false positives? Please remember that we do not give medical or legal advice.

Subj: Pre-employment drug screening
Date: 11/7/2009
I have been taking Zantac every day for 2 weeks because of stomach problems. I have a pre-employment drug screening on Monday (today is Saturday). If I do not take Zantac until after the test, is there still a possibility of a false negative on a drug test that is 2 days away? Also, I take the OTC product, Estroven, which contains Black Cohosh – can that create a false positive on a urine test? Thanks.


AskDocWeb: The elimination half-life of Zantac (ranitidine hydrochloride) is 2.5 to 3 hours so it should be out of your system within 24 hours. Estroven and other products containing Black Cohosh have not been reported to show up on urine drug tests.

Subj: False positive drug screen for THC
Date: 11/8/2009
I am on probation and recently had a false positive drug screen for THC. I have not been around any pot in more that 5 months, but I had been sick in bed for 8 days before the screen. I went to the Dr. the day after the screen and was diagnosed with a GI tract infection and had large ketones in my urine. Would this have any connection to the positive screen? I was also taking immodium, kaopectate, ibuprophen, and alleve at the recommended doses and times while I was sick. I recovered six days after going to the Dr.


AskDocWeb: Both Ibuprofen and Aleve are reported to sometimes show up as a false positive for Marijuana (THC). Having both in your system would increase the chances of a false positive on a urine drug test.

Subj: Drug test for THC
Date: 11/8/2009
I recently failed a drug test for THC. I do not use marijuana. I had a hair sample tested after the fact and it was negative for a twelve month period encompassing the failed urine test. The only source of THC I cam in contact with is lotions that contain hemp oil. I have read conflicting info on the posibility of failing a drug test from hemp oil. I also suffer from chronic hives and wonder if this would be a factor.


AskDocWeb: Hives have not been mentioned as a possible cause for false positives. We suspect that your positive result was from the hemp oil. It may be a natural oil but it is derived from the marijuana plant.

Subj: Cymbalta
Date: 11/9/2009
Can cymbalta give a false positive opiate result?


AskDocWeb: Cymbalta (duloxetine hydrochloride) has not been reported to give a false positive for anything on urine drug tests.

Subj: Hair follicle test?
Date: 11/9/2009
What meds would cause a hair follicle sample to show cocaine when I have none in my system.


AskDocWeb: Sorry Kelley, our research only covers urine testing, not hair tests.

Subj: Xenadrine Rfa-X?
Date: 11/13/2009
Hi my husband has been clean for over 2 months but he weighs about 280 and he was taking Xenadrine Rfa-X there fat burner pills he keeps coming up with high THC level but they said before it was real low and the last 5 times they have been high why is this happening.


AskDocWeb: It is not clear just what ingredients are in Xenadrine rfa-x. Most such products are developed from ephedrine, although they may claim that they don’t contain ephedrine directly. Ephedra, ephedrine, and Ephedrineis are known to give a positive on urine drug tests. (See references 2, 3, 11, 16, 18, 29, 30, and 32)

Subj: Fentanyl?
Date: 11/14/2009
I am taking fentanyl, can that give a false positive for any illegal drugs?


AskDocWeb: Fentanyl is not commonly tested for in most pre-employment situations, however, it is being increasing included in random testing. The use of Fentanyl should not cause a false positive because it has very poor cross-reactivity against the antibodies used in opiate testing.

Subj: Hydrocodone
Date: 11/16/2009
I was recently drug tested ( SAP 7 with nitrite)) at my place of employment “for suspicion” as I had several panic attacks. I have been dx with anxiety disorder, as my mom has been very ill, probably dementia, since January of this year. I am prescribed xanax, hydrocodone for chronic migraine headaches which are stress induced, and ambien for sleep. I was told that sometimes the hydrocodone can produce a false positive for oxycontin. That scared me because I have never taken oxycontin, but of course can provide a script for the hydrocodone.


Subj: Random drug tests
Date: 11/15/2009
My husband is taking two drugs 15 APAP # 3 Tab and Methocarbamol. He has been experience symptoms as if he were taking cocaine. Could these products be causing these symptoms? Please advise. He gets random drug tests and we do not want the agency to think he is lying. Thank you.


AskDocWeb: The side effects of Methocarbamol (Robaxin) alone could account for most of his symptoms. Here is a partial list of adverse reactions and side effects to Methocarbamol:

  • Amnesia
  • Anaphylactic reaction
  • Angioneurotic edema
  • Blurred vision
  • Bradycardia
  • Confusion
  • Conjunctivitis
  • Diplopia
  • Dizziness
  • Drowsiness
  • Dyspepsia
  • Fever
  • Flushing
  • Headache
  • Hypotension
  • Insomnia
  • Jaundice (including cholestatic jaundice)
  • Leukopenia
  • Lightheadedness
  • Loss of muscle coordination
  • Metallic taste
  • Nasal congestion
  • Nausea
  • Nystagmus
  • Pruritus
  • Rash
  • Sedation
  • Seizures (including grand mal)
  • Syncope
  • Thrombophlebitis
  • Urticaria
  • Vertigo
  • Vomiting

Make sure that the people doing the test know he is taking prescription drugs. If his test comes back positive for anything then you may have to get a GC/MS confirmation test but that is unlikely.

Subj: Mouth swab?
Date: 11/16/2009
My son tested positive for amphetamine on a mouth swab. He has been clean for 4.5 months. He passed his urine test the same day. No over the counter drugs either. What could cause a swab to test positive?


AskDocWeb: The first possibility that comes to mind is that the exposure was recent enough to show up orally but too recent to show up in the urine. We are not saying that is the case here, just that it is a possibility.

Subj: Drug test?
Date: 11/16/2009
Will acai berry, hoodia gordonii, or cha de bugre show up as any illicit drug on a drug test?


AskDocWeb: None of those are on the list of products that might cause a false positive.

Subj: Positive test for PCP
Date: 11/17/2009
I came home on a Friday night after being out of town for a while. I got up on sat not feeling well so I took two dayquil tablets and layed back down. I got up about 4 hours later and had what appeared to be a seizure. An ambulance was called. I seized for 4 hours. They done a urine test and I found out from my neurologist that they got a positive test for PCP. I have never done drugs in my life. The dayquil box states it has acetaminophen 325mg, dextromethorphan hbr 10mg, and phenyllephrine hci 5 mg. I know the EMTs stated my pupils was extremely dilated. Can you please help me understand this?


AskDocWeb: Sorry Mary, the only drugs that have been reported to cause a false positive for PCP are Diazepam (Reference 29), Diphenhydramine (Reference 24), Effexor Tablets (venlafaxine hydrochloride) (Reference 27 and 33), and Ketamine (Reference 16 and 32).

Subj: Drug test showed amphetamines
Date: 11/18/2009
I am on armour thriod, hydrocodone trazodone, tramadol zantac, clonidine, advair, and take an herb called kava kava and took a drug test that showed amphetamines which I absolutly do not use, would any of these cause this?


Yes, Zantac has been reported to sometimes show up as a false positive for Amphetamines (Reference 30).

Subj: Tested positive for amphetamines
Date: 11/19/2009
I gave birth to my son on Oct. 18, ’09 and when I was in labor the nurse gave me a routine urine test. A couple hours later they came back and asked my family to leave the room so they could give me an epedural. She then told my fiance and I that I tested positive for amphetamines. She told me then that she could not give me the epedural because of that and treated me like a drug addict, questioning me on my methamphetamine use and such. So I was forced to give birth all natural. I would not and did not use ANY drugs during my pregnancy. I was taking Buspirone, Neevo vitamins, and I got a cold about a week before I delivered my son and took regular tylenol and Halls cough drops but the only ingredient that was active was menthol. DHS was notified and they treated me harshly. The main point is that my son’s blood was tested and it came back negative. All I was given was a urine test. They eventually let me home after alot of help from the pediatrican who tested him and my mother in law. I would really just like some help figuring out How and why I would test positive for that. If you could help I would really appreciate that. Thank you.


AskDocWeb: Sorry to hear that you were forced to go through natural childbirth. If you had known that urine tests have an error rate you could have contested the results and demanded other testing. The whole concept of false positives is news to many people until it happens to them. Several of the tylenol products show up on this list.

Subj: OMG, positive for marijuana!
Date: 11/19/2009
I just took a drug test today and it showed positive for marijuana! OMG…I have not used any kind of recreational drug in about 7 months and never marijuana. My probation officer took the test twice. I am taking Naproxen 500 mg and Advil PM along with many other prescription drugs. (Nexium, EstraTest, blood pressure med., Green Tea diet pills, diuretic, Levoxyl, Wellbutrin, Pravachol) I have been very distressed because a positive drug test can mean jail time for me. Will Naproxen 500mg show positive for marijuana? Will Advil pm show positive for marijuana? The test was sent to the lab, and I pray that they will be able to know that it is not marijuana..Thanks for this site


AskDocWeb: There are several references that say Advil sometimes shows up as a false positive for THC or Marijuana (1, 14, 16, 18, 20, 26, and 29) and one for Apo-Naproxen (Reference 1).

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