Cyclobenzaprine Side Effects

Brand Names: Flexeril, Amrix

Please note - some side effects for Cyclobenzaprine may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA at http://www.fda.gov/medwatch/ or 1-800-FDA-1088 (1-800-332-1088).

Side Effects of Cyclobenzaprine - for the Consumer

Cyclobenzaprine

All medicines may cause side effects, but many people have no, or minor, side effects. Check with your doctor if any of these most COMMON side effects persist or become bothersome when using Cyclobenzaprine:

Constipation; diarrhea; dizziness; drowsiness; dry mouth; fatigue; nausea; nervousness; stomach pain or upset.

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); chest pain; confusion; fainting; fast or irregular heartbeat; mental or mood changes; numbness of an arm or a leg; one-sided weakness; seizures; sudden severe stomach pain; severe dizziness or vomiting; speech or vision problems; trouble urinating; yellowing of the skin or eyes.

Cyclobenzaprine Extended-Release Capsules

All medicines may cause side effects, but many people have no, or minor, side effects. Check with your doctor if any of these most COMMON side effects persist or become bothersome when using Cyclobenzaprine Extended-Release Capsules:

Constipation; dizziness; drowsiness; dry mouth; fatigue; nausea; stomach pain or upset.

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); chest pain; confusion; fainting; fast or irregular heartbeat; mental or mood changes; numbness of an arm or a leg; one-sided weakness; seizures; severe dizziness or vomiting; speech or vision problems; sudden severe stomach pain; trouble urinating; yellowing of the skin or eyes.

Cyclobenzaprine Side Effects - for the Professional

Cyclobenzaprine

Incidence of most common adverse reactions in the 2 double-blind‡, placebo-controlled 5 mg studies (incidence of > 3% on Cyclobenzaprine hydrochloride tablets 5 mg):

Adverse reactions which were reported in 1% to 3% of the patients were: abdominal pain, acid regurgitation, constipation, diarrhea, dizziness, nausea, irritability, mental acuity decreased, nervousness, upper respiratory infection, and pharyngitis.

The following list of adverse reactions is based on the experience in 473 patients treated with Cyclobenzaprine hydrochloride tablets 10 mg in additional controlled clinical studies, 7607 patients in the post-marketing surveillance program, and reports received since the drug was marketed. The overall incidence of adverse reactions among patients in the surveillance program was less than the incidence in the controlled clinical studies.

The adverse reactions reported most frequently with Cyclobenzaprine hydrochloride were drowsiness, dry mouth and dizziness. The incidence of these common adverse reactions was lower in the surveillance program than in the controlled clinical studies:

‡Note: Cyclobenzaprine hydrochloride tablets 10 mg data are from one clinical trial. Cyclobenzaprine hydrochloride tablets 5 mg and placebo data are from two studies.

Among the less frequent adverse reactions, there was no appreciable difference in incidence in controlled clinical studies or in the surveillance program. Adverse reactions which were reported in 1% to 3% of the patients were: fatigue/tiredness, asthenia, nausea, constipation, dyspepsia, unpleasant taste, blurred vision, headache, nervousness, and confusion.

The following adverse reactions have been reported in post-marketing experience or with an incidence of less than 1% of patients in clinical trials with the 10 mg tablet:

Body as a Whole:  Syncope; malaise.
Cardiovascular:  Tachycardia; arrhythmia; vasodilatation; palpitation; hypotension.
Digestive:  Vomiting; anorexia; diarrhea; gastrointestinal pain; gastritis; thirst; flatulence; edema of the tongue; abnormal liver function and rare reports of hepatitis, jaundice and cholestasis.
Hypersensitivity:  Anaphylaxis; angioedema; pruritus; facial edema; urticaria; rash.
Musculoskeletal:  Local weakness.
Nervous System and Psychiatric:  Seizures, ataxia; vertigo; dysarthria; tremors; hypertonia; convulsions; muscle twitching; disorientation; insomnia; depressed mood; abnormal sensations; anxiety; agitation; psychosis, abnormal thinking and dreaming; hallucinations; excitement; paresthesia; diplopia.
Skin:  Sweating.
Special Senses:  Ageusia; tinnitus.
Urogenital:  Urinary frequency and/or retention.

Causal Relationship Unknown

Other reactions, reported rarely for Cyclobenzaprine hydrochloride under circumstances where a causal relationship could not be established or reported for other tricyclic drugs, are listed to serve as alerting information to physicians:

Body as a Whole:  Chest pain; edema.
Cardiovascular:  Hypertension; myocardial infarction; heart block; stroke.
Digestive:  Paralytic ileus; tongue discoloration; stomatitis; parotid swelling.
Endocrine:  Inappropriate ADH syndrome.
Hematic and Lymphatic:  Purpura; bone marrow depression; leukopenia; eosinophilia; thrombocytopenia.
Metabolic, Nutritional and Immune:  Elevation and lowering of blood sugar levels; weight gain or loss.
Musculoskeletal:  Myalgia.
Nervous System and Psychiatric:  Decreased or increased libido; abnormal gait; delusions; aggressive behavior; paranoia; peripheral neuropathy; Bell's palsy; alteration in EEG patterns; extrapyramidal symptoms.
Respiratory:  Dyspnea.
Skin:  Photosensitization; alopecia.
Urogenital:  Impaired urination; dilatation of urinary tract; impotence; testicular swelling; gynecomastia; breast enlargement; galactorrhea.

Side Effects by Body System

Nervous system

Elderly patients may be particularly susceptible to the sedation and confusion which may accompany cyclobenzaprine therapy.

Nervous system side effects are common and include drowsiness in up to 40% of treated patients and dizziness in up to 11%. Fatigue, asthenia, headache, nervousness, blurred vision, and confusion have also been reported.

Other

Other side effects have included anticholinergic effects such as dry mouth (in as many as 27% of treated patients), and, less frequently, dry skin, blurry vision, constipation, and an organic brain syndrome. Paradoxical sweating has also been reported.

Psychiatric

Psychiatric side effects including mania and psychosis have been reported rarely. A case of hallucinations has also been reported.

Hypersensitivity

Hypersensitivity side effects have included rash, angioedema, and pruritus. Anaphylaxis has been reported rarely.

Cardiovascular

Cardiovascular side effects have included cardiac arrhythmias, tachycardia, and hypotension.

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