Note: This document contains side effect information about gabapentin enacarbil. Some of the dosage forms listed on this page may not apply to the brand name Horizant.

Common side effects of Horizant include: dizziness, drowsiness, and sedated state. Other side effects include: irritability. See below for a comprehensive list of adverse effects.

Applies to gabapentin enacarbil: oral tablet extended release

Along with its needed effects, gabapentin enacarbil (the active ingredient contained in Horizant) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking gabapentin enacarbil:

More common

• Bloating or swelling of the face, arms, hands, lower legs, or feet
• discouragement
• feeling sad or empty
• irritability
• lack of appetite
• loss of interest or pleasure
• rapid weight gain
• tingling of the hands or feet
• tiredness
• trouble concentrating

Incidence not known

• Black, tarry stools
• bloody or cloudy urine
• changes in behavior
• chest pain or discomfort
• chills or fever
• confusion
• difficulty with breathing
• dizziness or lightheadedness
• fainting
• fast heartbeat
• nausea or vomiting
• painful or difficult urination
• rapid, shallow breathing
• rash
• sore throat
• sores, ulcers, or white spots on the lips or in the mouth
• swelling of the face, feet, or lower legs
• swollen, painful, or tender lymph glands in the neck, armpit, or groin
• thoughts of killing oneself
• unusual bleeding or bruising
• upper right abdominal or stomach pain
• yellow eyes and skin

Some side effects of gabapentin enacarbil may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

• Lack or loss of strength
• sleepiness or unusual drowsiness

Less common

• Blurred vision
• decreased interest in sexual intercourse
• dry mouth
• excess air or gas in the stomach or intestines
• inability to have or keep an erection
• sensation of spinning
• weight gain

Applies to gabapentin enacarbil: compounding powder, oral capsule, oral solution, oral tablet, oral tablet extended release

Common (1% to 10%): Peripheral edema, vasodilation, hypertension

Rare (less than 0.1%): Atrial fibrillation, heart failure, myocardial infarction, cerebrovascular accident, ventricular extrasystoles, bradycardia, premature atrial contraction, pericardial rub, heart block, pericardial effusion, pericarditis

Postmarketing reports: Cardiac arrest, chest pain, palpitation, tachycardia

Common (1% to 10%): Abrasion, facial edema, purpura, rash, pruritus, acne

Uncommon (0.1% to 1%): Alopecia, eczema, dry skin, increased sweating, urticaria, hirsutism, seborrhea, cyst, herpes simplex

Rare (less than 0.1%): Stevens-Johnson syndrome, angioedema, erythema multiforme, drug rash (with eosinophilia and systemic symptoms), herpes zoster, skin discolor, skin papules, photosensitive reaction, psoriasis, desquamation, maceration, skin nodules, subcutaneous nodule, melanosis, skin necrosis, local swelling

Frequency not reported: DRESS/multiorgan hypersensitivity

Rare (less than 0.1%): Hyperthyroid, hypothyroid, goiter, hypoestrogenism, ovarian failure, epididymitis, cushingoid appearance

Common (1% to 10%): Diarrhea, dry mouth or throat, constipation, nausea, vomiting, dyspepsia, dental abnormalities, gingivitis, abdominal pain, flatulence

Uncommon (0.1% to 1%): Glossitis, gum hemorrhage, thirst, stomatitis, increased salivation, gastroenteritis, hemorrhoids, bloody stools, fecal incontinence

Rare (less than 0.1%): Pancreatitis, dysphagia, eructation, pancreatitis, peptic ulcer, colitis, blisters in mouth, tooth discoloration, perlèche, salivary gland enlarged, lip hemorrhage, esophagitis, hiatal hernia, hematemesis, proctitis, irritable bowel syndrome, rectal hemorrhage, esophageal spasm

Frequency not reported: Dehydration

The most common adverse reactions associated with the use of this drug were dizziness, somnolence, and peripheral edema.

Common (1% to 10%): Incontinence, impotence

Uncommon (0.1% to 1%): Hematuria, dysuria, urinary frequency, cystitis, urinary retention, vaginal hemorrhage, amenorrhea, dysmenorrhea, menorrhagia

Frequency not reported: Breast hypertrophy, gynecomastia, sexual dysfunction (including changes in libido, ejaculation disorders, and anorgasmia)

Common (1% to 10%): Leucopenia, purpura

Uncommon (0.1% to 1%): Anemia, lymphadenopathy

Rare (less than 0.1%): Thrombocytopenia, thrombophlebitis, leukocytosis, lymphocytosis, increased bleeding time

Frequency not reported: Blood creatine phosphokinase increased, coagulation defect

Rare (less than 0.1%): Hepatitis, jaundice, elevated liver function tests SGOT (AST), SGPT (ALT), and bilirubin, hepatomegaly, hepatotoxicity

Very rare (less than 0.01%): Hypersensitivity syndrome, a systemic reaction with a variable presentation that can include fever, rash, hepatitis, lymphadenopathy, eosinophilia, and sometimes other signs and symptoms

Common (1% to 10%): Weight gain, hyperglycemia

Postmarketing reports: Hyponatremia

Common (1% to 10%): Back pain, arthralgia, myalgia, twitching

Uncommon (0.1% to 1%): Tendonitis, arthritis, joint stiffness, joint swelling

Frequency not reported: Rhabdomyolysis, myoclonus

Postmarketing reports: Elevated creatine kinase, rhabdomyolysis

Very common (10% or more): Somnolence (21%), dizziness (17%), ataxia (13%)

Common (1% to 10%): Abnormal gait, incoordination, neuralgia, tremor, dysarthria, hyperkinesia, seizures, dysarthria, paresthesia, hypesthesia, coordination abnormal, increased/decreased/absent reflexes, vertigo

Uncommon (less than 1%): Hypokinesia

Rare (less than 0.1%): Movement disorders (e.g., choreoathetosis, dyskinesia, dystonia), loss of consciousness

Frequency not reported: Withdrawal precipitated seizure/status epilepticus

Postmarketing reports: Movement disorder

Common (1% to 10%): Amblyopia, conjunctivitis, diplopia, nystagmus

Uncommon (0.1% to 1%): Cataract, dry eyes, eye pain, visual field defect, photophobia, bilateral or unilateral ptosis, eye hemorrhage, hordeolum, eye twitching

Rare (less than 0.1%): Eye itching, abnormal accommodation, eye focusing problem, watery eyes, retinopathy, glaucoma, iritis, corneal disorders, lacrimal dysfunction, degenerative eye changes, blindness, retinal degeneration, miosis, chorioretinitis, strabismus

Uncommon (0.1% to 1%): Breast cancer

Rare (less than 0.1%): Non-Hodgkin's lymphoma

Very common (10% or more): Fatigue (11%), fever (11%)

Common (1% to 10%): Asthenia, accidental injury, otitis media, tremor, pain

Rare (0.01% to 0.1%): Tinnitus

Very rare (less than 0.01%): Sudden unexplained death in patients with epilepsy

Frequency not reported: Sleepwalking, withdrawal symptoms, hearing loss, earache, tinnitus, inner ear infection, otitis, taste loss, unusual taste, ear fullness, perforated ear drum, sensitivity to noise, eustachian tube dysfunction, otitis externa, odd smell, labyrinthitis

Common (1% to 10%): Abnormal thinking, amnesia, depression, hostility, confusion, emotional liability, anxiety, nervousness, insomnia

Uncommon (0.1% to 1%): Mental impairment

Rare (less than 0.1%): Hallucinations

Frequency not reported: Suicidal behavior and ideation, hypomania

Rare (less than 0.1%): Acute renal failure

Common (1% to 10%): Pharyngitis, dyspnea, cough, bronchitis, respiratory infection, rhinitis

Rare (less than 0.1%): Pulmonary thrombosis, pulmonary embolism

Frequency not reported: Pseudo-croup, hoarseness