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Mio-Rel Side Effects

Generic Name: orphenadrine

Note: This page contains information about the side effects of orphenadrine. Some of the dosage forms included on this document may not apply to the brand name Mio-Rel.

For the Consumer

Applies to orphenadrine: oral tablet, oral tablet extended release

Other dosage forms:

In addition to its needed effects, some unwanted effects may be caused by orphenadrine (the active ingredient contained in Mio-Rel). In the event that any of these side effects do occur, they may require medical attention.

Major Side Effects

You should check with your doctor immediately if any of these side effects occur when taking orphenadrine:

  • Chest pain
  • chills
  • cough
  • fever
  • hallucinations (seeing, hearing, or feeling things that are not there)
  • headache
  • shortness of breath, troubled breathing, tightness in chest, and/or wheezing
  • skin rash, hives, itching, or redness
  • sores, ulcers, or white spots on lips or in mouth
  • swollen and/or painful glands
  • unusual bruising or bleeding
  • unusual tiredness or weakness
Incidence not known:
  • Abdominal or stomach pain
  • diarrhea
  • fainting
  • fast, pounding irregular heartbeat or pulse
  • glaucoma
  • joint or muscle pain
  • nausea
  • numbness or tingling of face, hands, or feet
  • redness and soreness of eyes
  • swelling of feet or lower legs
  • vomiting

If any of the following symptoms of overdose occur while taking orphenadrine, get emergency help immediately:

Symptoms of overdose:
  • Blurred vision
  • confusion, delirium, or hallucinations
  • constipation
  • difficult urination
  • drowsiness
  • dry eyes, mouth, nose, or throat
  • eye pain
  • flushing or redness of face
  • troubled breathing

Minor Side Effects

Some of the side effects that can occur with orphenadrine may not need medical attention. As your body adjusts to the medicine during treatment these side effects may go away. Your health care professional may also be able to tell you about ways to reduce or prevent some of these side effects. If any of the following side effects continue, are bothersome or if you have any questions about them, check with your health care professional:

Less common or rare:
  • Dizziness or lightheadedness
  • excitement, irritability, nervousness, or restlessness
  • headache
  • muscle weakness
  • unusually large pupils of eyes
Incidence not known:
  • Anxiety
  • deep or fast breathing with dizziness
  • itching skin
  • mental confusion
  • numbness of feet, hands and around mouth
  • trembling or shaking of hands or feet shakiness in legs, arms, hands, or feet

For Healthcare Professionals

Applies to orphenadrine: compounding powder, injectable solution, oral tablet extended release

Nervous system

Nervous system side effects have included headache, light-headedness, dizziness, drowsiness, syncope and tremor. Infrequently, elderly patients have experienced mental confusion.[Ref]


Ocular side effects have included blurred vision, dilatation of pupils, and increased ocular tension.[Ref]


Cardiovascular side effects have included tachycardia and palpitations.[Ref]


Genitourinary side effects have included urinary hesitancy and retention.[Ref]


Gastrointestinal side effects have included dry mouth, nausea, vomiting, and gastric irritation.[Ref]


Musculoskeletal side effects have included weakness.[Ref]


Dermatologic side effects have included pruritus, and rarely, urticaria and other dermatosis.[Ref]


Psychiatric side effects have included hallucinations and agitation.[Ref]


Hematologic side effects have included very rare cases of aplastic anemia, however, no causal relationship has been established.[Ref]


1. "Product Information. Norflex (orphenadrine)." 3M Pharmaceuticals, St. Paul, MN.

Not all side effects for Mio-Rel may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

Disclaimer: Every effort has been made to ensure that the information provided is accurate, up-to-date and complete, but no guarantee is made to that effect. In addition, the drug information contained herein may be time sensitive and should not be utilized as a reference resource beyond the date hereof. This material does not endorse drugs, diagnose patients, or recommend therapy. This information is a reference resource designed as supplement to, and not a substitute for, the expertise, skill , knowledge, and judgement of healthcare practitioners in patient care. The absence of a warning for a given drug or combination thereof in no way should be construed to indicate safety, effectiveness, or appropriateness for any given patient. does not assume any responsibility for any aspect of healthcare administered with the aid of materials provided. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the substances you are taking, check with your doctor, nurse, or pharmacist.