Does Cephalexin show up on a drug test? 

Does Cephalexin show up on a drug test? 

No, Cephalexin does not show up on a drug test. Cephalexin (Keflex) is a beta-lactam antibiotic which is neither a drug of abuse nor a controlled substance. 

This antibiotic is not included in the panel of drugs that are usually tested. Cephalexin is also not known to cause a false positive for any of the scheduled drugs. 

So, if you are being treated with this antibiotic and have a drug test coming up, it will most likely not make you fail it. Some people skip their meds to avoid getting a false positive, which is not something you should do when you have an active bacterial infection in your body. 

Getting a false positive is a common thing nowadays because of the cross-reactivity of commonly used prescription and OTC meds with the antibodies which are supposed to bind to drugs of abuse – if present in the body (1). 

What to do if you’re concerned about Cephalexin and drug testing?

Talking to your doctor or the test-conducting authorities should be your first course of action if you have concerns regarding Cephalexin and drug testing. They can tell you more about the particular drug testing procedure being used and whether or not Cephalexin might result in a positive test.

It is also important to continue taking Cephalexin as directed by your healthcare provider. It is an antibiotic and bacterial infections should be managed properly. Skipping antibiotics just to avoid getting a false positive drug test is not a good approach.

Although Cephalexin does not cause a false positive and even if it does, it won’t affect you negatively. This is a common mishap with preliminary drug immunoassays and going for accurate testing procedures – like Gas Chromatography-Mass spectrometry can solve this problem (2).

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Alyson Schwebach, Jennifer Ball. Urine Drug Screening: Minimizing False Positives and False Negatives to Optimize Patient Care. US Pharm. 2013;38(12):1-6. Available from:


Ramoo B, Funke M, Frazee C, Garg U. Comprehensive Urine Drug Screen by Gas Chromatography/Mass Spectrometry (GC/MS). Methods Mol Biol. 2016;1383:125-31. doi: 10.1007/978-1-4939-3252-8_15. PMID: 26660182. Available from: