Quick answer
Muscle relaxers (Flexeril, Soma, tizanidine) is typically detectable in urine for 2–4 days (cyclobenzaprine half-life ~18 h) after any use. It is screened on standard 12-panel drug tests.
Screened on: 12-panel
Typical cutoff: Not directly screened; cyclobenzaprine cross-reacts on tricyclic-antidepressant (TCA) screens.
Detection window by test type
| urine | |
|---|---|
| Any use | 2–4 days (cyclobenzaprine half-life ~18 h) |
| saliva | |
| Any use | n/a |
| hair | |
| Any use | n/a |
| blood | |
| Any use | n/a |
Ranges reflect typical published detection windows and vary with dose, frequency, body composition, hydration and the assay used.
Key details
Muscle relaxers aren't panel targets, BUT Flexeril (cyclobenzaprine — structurally a TCA cousin) flags tricyclic screens that some 12-panel-plus cups carry, and Soma's metabolite meprobamate is itself a monitored barbiturate-like compound.
If a TCA strip flags after Flexeril, the MRO matches your prescription and reports accordingly.
False positives & cross-reactivity
- Cyclobenzaprine → TCA-screen FP: documented. Quetiapine/hydroxyzine share TCA-strip risk.
Frequently asked questions
How long does muscle relaxers (flexeril, soma, tizanidine) stay in your system?
In urine, typical detection is 2–4 days (cyclobenzaprine half-life ~18 h) (any use). Hair can detect use for up to 90 days and saliva/blood windows are usually shorter.
Will muscle relaxers (flexeril, soma, tizanidine) show up on a standard drug test?
Yes — Muscle relaxers (Flexeril, Soma, tizanidine) is screened on standard panels (12-panel).
Can anything cause a false positive for muscle relaxers (flexeril, soma, tizanidine)?
Cyclobenzaprine → TCA-screen FP: documented. Quetiapine/hydroxyzine share TCA-strip risk.
How accurate are these detection windows?
They are typical ranges from published literature and assay documentation, not guarantees. Clearance depends on dose, frequency, metabolism and the specific test cutoff used.
Related substances
Cite this page
DrugPanels. “Muscle relaxers (Flexeril, Soma, tizanidine) Detection Time.” https://drugpanels.com/detection/muscle-relaxers/. Accessed 2026-09-10.
Sources
- Brahm NC et al., Commonly prescribed medications and potential false-positive drug test results, Mayo Clinic Proceedings 2008 — Mayo Clinic Proceedings — pubmed.ncbi.nlm.nih.gov
- Immunoassay cross-reactivity and validation documentation (FDA 510(k) summaries) — U.S. Food and Drug Administration — accessdata.fda.gov
Detection windows describe typical ranges from the published literature and assay documentation; individual results vary. See our methodology.