What the FDA labels say about taking them together
Hydromorphone and metaxalone
Hydromorphone's FDA label of May 14, 2026 names metaxalone in its drug interactions section; metaxalone's label does not name hydromorphone itself but warns about its class (Opioids (opioid agonists)). The hydromorphone label: “The concomitant use of opioids with other drugs that affect the serotonergic neurotransmitter system has resulted in serotonin syndrome.”
Check it at the source: the hydromorphone FDA label on DailyMed (effective May 14, 2026, Rhodes Pharmaceuticals LLC); the metaxalone FDA label on DailyMed (effective January 11, 2023, Amneal Pharmaceuticals of New York LLC).
What does the hydromorphone label say about metaxalone?
Hydromorphone label, drug interactionsSerotonergic Drugs Clinical Impact: The concomitant use of opioids with other drugs that affect the serotonergic neurotransmitter system has resulted in serotonin syndrome. … neurotransmitter system (e.g., mirtazapine, trazodone, tramadol), certain muscle relaxants (i.e., cyclobenzaprine, metaxalone), monoamine oxidase (MAO) inhibitors (those intended to treat psychiatric disorders and also others, such as linezolid and intravenous methylene blue).
Source: FDA drug label (Hydromorphone Hydrochloride, NDA019034), Fresenius Kabi USA, LLC, effective July 15, 2026 (SPL set e034eb96-03e0-46e1-8b92-5e1f94555e7b), via openFDA
Source: FDA drug label (Hydromorphone Hydrochloride), Rhodes Pharmaceuticals LLC, effective May 14, 2026 (SPL set 37565441-0d95-4743-a695-d7b3326f58a1), via openFDA; the full label on DailyMed
What does the metaxalone label say about hydromorphone?
Metaxalone's label does not name hydromorphone itself; it warns about its class (Opioids (opioid agonists)):
Metaxalone label, warnings and precautionsCases of serotonin syndrome, a potentially life-threatening condition, have been reported during concomitant use of metaxalone (within the recommended dosage range) and other serotonergic drugs [see Drug Interactions (7) ] and with the use of metaxalone as the only serotonergic drug taken at a dosage higher than the recommended dosage [see Overdosage (10) ]. …
Metaxalone label, drug interactionsDiscontinue metaxalone if serotonin syndrome is suspected. Examples of serotonergic drugs include: selective serotonin reuptake inhibitors (SSRIs), serotonin and norepinephrine reuptake inhibitors (SNRIs), tricyclic antidepressants (TCAs), triptans, 5-HT3 receptor antagonists, opioids (particularly fentanyl, meperidine, and methadone), drugs that affect the serotonin neurotransmitter system (e.g., mirtazapine, trazodone, tramadol), monoamine oxidase (MAO) inhibitors (those intended to treat psychiatric disorders …
Source: FDA drug label (Metaxalone), Amneal Pharmaceuticals of New York LLC, effective January 11, 2023 (SPL set f06f2b96-3684-483c-89f7-6c9201fd4664), via openFDA; the full label on DailyMed
These are the labels' own sentences. PlainMeds does not grade interactions; a pharmacist or prescriber can say what they mean for one person's medicines.
Both medicines on the record
| Hydromorphone | Metaxalone | |
|---|---|---|
| Labeled for | Pain | Muscle spasms and spasticity |
| Boxed warning | Yes | No |
| Pharmacy cost (NADAC) | $0.219 per tablet 4 mg tablet | $0.452 per tablet 800 mg tablet |
| Shortage now | In shortage | No current entry |
Source: FDA NDC Directory, CMS NADAC of October 7, 2026 and the FDA Drug Shortage Database (FDA files October 8, 2026)
What next?
- Check more medicines together
- up to five at once