Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes Neurontin (Gabapentin). If you are concerned about side effects, discuss the risks and benefits of Neurontin (Gabapentin) with your doctor.

The following side effects have been reported by at least 1% of people taking Neurontin (Gabapentin). Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• dizziness
• drowsiness
• fatigue
• swelling of feet or ankles
• trouble sleeping

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not check with your doctor or seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• abnormal heartbeat or heart palpitations
• agitation
• changes in blood sugar and decreased blood sugar control (low blood sugar – cold sweat, cool pale skin, headache, fast heartbeat, weakness; high blood sugar – frequent urination, increased thirst, excessive eating, unexplained weight loss, poor wound healing, infections, fruity breath odour)
• chest pain
• confusion
• hallucinations (e.g., seeing or hearing things that aren't there)
• inability to control urination
• poor coordination
• rapid or pounding heartbeat (palpitations)
• ringing in the ears
• signs of Depression (e.g., poor concentration, changes in weight, changes in sleep, decreased interest in activities, thoughts of suicide)
• symptoms of low sodium in the blood (e.g., tiredness, weakness, confusion, achy, stiff or uncoordinated muscles)
• symptoms of liver problems (e.g., abdominal pain, persistent vomiting, feeling unwell, Fever, itching, yellowing of the skin and eyes, dark urine)
• unexplained muscle pain or tenderness, muscle weakness, dark urine with nausea or vomiting
• unusual changes in mood

Stop taking the medication and seek immediate medical attention if any of the following occur:

• hallucinations (seeing or hearing things that aren't there)
• loss of consciousness
• signs of a serious allergic reaction (e.g., swelling of face or throat, Hives, or difficulty breathing)
• signs of a severe skin reaction such as blistering, peeling, a rash covering a large area of the body, a rash that spreads quickly, or a rash combined with fever or discomfort
• slow, shallow or weak breathing
• thoughts of hurting yourself or others
• worsening seizures

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking Neurontin (Gabapentin).

Capsules

100 mg
Each hard gelatin Coni-Snap capsule with white opaque body and cap printed with "PD" on one side and "Neurontin/100 mg" on the other contains 100 mg of Neurontin (Gabapentin). Nonmedicinal ingredients: cornstarch, lactose, and talc; capsule shell: FD&C Blue No. 2, gelatin, red iron oxide, silicon dioxide, sodium lauryl sulfate, titanium dioxide, and yellow iron oxide.

300 mg
Each hard gelatin Coni-Snap capsule with yellow opaque body and cap printed with "PD" on one side and "Neurontin/300 mg" on the other contains 300 mg of Neurontin (Gabapentin). Nonmedicinal ingredients: cornstarch, lactose, and talc; capsule shell: FD&C Blue No. 2, gelatin, red iron oxide, silicon dioxide, sodium lauryl sulfate, titanium dioxide, and yellow iron oxide.

400 mg
Each hard gelatin Coni-Snap capsule with orange opaque body and cap printed with "PD" on one side and "Neurontin/400 mg" on the other contains 400 mg of Neurontin (Gabapentin). Nonmedicinal ingredients: cornstarch, lactose, and talc; capsule shell: FD&C Blue No. 2, gelatin, red iron oxide, silicon dioxide, sodium lauryl sulfate, titanium dioxide, and yellow iron oxide.

Tablets

600 mg
Each white, elliptical, film-coated tablet with "Neurontin 600" printed on one side contains 600 mg of Neurontin (Gabapentin). Nonmedicinal ingredients: ammonium hydroxide, black iron oxide, candelilla wax, copolyvidone, cornstarch, hydroxypropyl cellulose, magnesium stearate, poloxamer 407 NF, and talc.

800 mg
Each white, elliptical, film-coated tablet with "Neurontin 800" printed on one side contains 800 mg of Neurontin (Gabapentin). Nonmedicinal ingredients: candelilla wax, copolyvidone, cornstarch, hydroypropylcellulose, hypromellose, magnesium stearate, poloxamer 407 NF, red iron oxide, yellow iron oxide, and talc.

Do not take Neurontin (Gabapentin) if you are allergic to Neurontin (Gabapentin) or any ingredients of Neurontin (Gabapentin).

There may be an interaction between Neurontin (Gabapentin) and any of the following:

• alcohol
• antacids containing magnesium or aluminum
• antihistamines (e.g., cetirizine, doxylamine, Diphenhydramine, Hydroxyzine, Loratadine)
• antipsychotics (e.g., Chlorpromazine, Clozapine, Haloperidol, Olanzapine, Quetiapine, Risperidone)
• azelastine
• benzodiazepines (e.g., Alprazolam, Diazepam, Lorazepam)
• brimonidine
• Buprenorphine
• Buspirone
• calcium carbonate
• cannabis
• chloral hydrate
• efavirenz
• Entacapone
• general anesthetics (medications used to put people to sleep before surgery)
• Mefloquine
• Methadone
• Mirtazapine
• muscle relaxants (e.g., Baclofen, Cyclobenzaprine, methocarbamol, orphenadrine)
• Nabilone
• narcotic pain relievers (e.g., Codeine, Hydrocodone,  Morphine, Oxycodone)
• Olopatadine
• Orlistat
• Pramipexole
• Ropinirole
• Rotigotine
• scopolamine
• other seizure medications (e.g., Carbamazepine, Clobazam, Ethosuximide, Levetiracetam, Phenobarbital, Phenytoin, primidone, Topiramate, Valproic acid, zonisamide)
• selective serotonin reuptake inhibitors (SSRIs; e.g., Citalopram, Fluoxetine, Paroxetine, Sertraline)
• sodium bicarbonate
• sodium oxybate
• suvorexant
• Tapentadol
• thalidomide
• tolcapone
• Tramadol
• Trazodone
• tricyclic antidepressants (e.g., Amitriptyline, Imipramine)
• Zolpidem
• Zopiclone

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with Neurontin (Gabapentin). Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the Nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or Allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use Neurontin (Gabapentin).

Alcohol and other medications that cause drowsiness: People taking Neurontin (Gabapentin) should not combine it with alcohol and avoid combining it with other medications, such as narcotic pain relievers, that cause drowsiness. Doing so can cause additional drowsiness and reduced breathing as well as increase the risk of opioid overdose, which can be dangerous and possibly life threatening.

Difficulty breathing: Neurontin (Gabapentin) can cause serious and life-threatening breathing problems. If you have breathing or lung problems, decreased kidney function, are taking other medications that can slow breathing, or if you are a senior, you are more at risk of experiencing breathing difficulties. If you experience slowed breathing or difficulty breathing, seek immediate medical attention.

Drowsiness/reduced alertness: If you have uncontrolled epilepsy, do not drive or handle potentially dangerous machinery. Neurontin (Gabapentin) may cause drowsiness, dizziness, or problems with coordination. Avoid any activity requiring mental alertness or physical coordination until you determine how Neurontin (Gabapentin) affects you.

Hypersensitivity syndrome: A Anaphylaxis (severe allergic reaction) called hypersensitivity syndrome has occurred for some people with the use of Neurontin (Gabapentin). Stop taking the medication and get immediate medical attention if you have symptoms of a severe allergic reaction, including fever, swollen glands, yellowing of the skin or eyes, or flu-like symptoms with skin rash or blistering.

Kidney function: Kidney Disease or reduced kidney function may cause Neurontin (Gabapentin) to build up in the body, causing side effects. If you have reduced kidney function or kidney disease, discuss with your doctor how Neurontin (Gabapentin) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Neurontin (Gabapentin), and whether any special monitoring is needed.

Stopping the medication: As with other medications used to control seizures, stopping Neurontin (Gabapentin) suddenly could increase the risk of seizures. Do not stop Neurontin (Gabapentin) suddenly. Ask your doctor how to safely and gradually stop the medication.

Suicidal or agitated behaviour: People taking Neurontin (Gabapentin) may feel agitated (restless, anxious, aggressive, emotional, and feeling not like themselves), or they may want to hurt themselves or others. If you experience these side effects or notice them in a family member who is taking Neurontin (Gabapentin), contact your doctor immediately. You should be closely monitored by your doctor for emotional and behaviour changes while taking Neurontin (Gabapentin).

Pregnancy: Neurontin (Gabapentin) crosses the placenta and may harm the developing baby if it is taken by the mother while she is pregnant. It should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking Neurontin (Gabapentin), contact your doctor immediately.

Breast-feeding: Neurontin (Gabapentin) passes into breast milk. If you are a breast-feeding mother and are taking Neurontin (Gabapentin), it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using Neurontin (Gabapentin) have not been established for children.

Seniors: Seniors are at an increased risk of side effects and may require a dose of Neurontin (Gabapentin) that is lower than usual due to reduced kidney function.