Description and Brand Names

Drug information provided by: Merative, Micromedex®

US Brand Name

  1. Abstral
  2. Actiq
  3. Fentora
  4. Onsolis
  5. Subsys


Fentanyl is used to treat severe pain in cancer patients. It is used for breakthrough cancer pain, which are flares of pain that “break through” after a routine pain medicine has been used. Fentanyl belongs to the group of medicines called opioid analgesics. It is only used in patients who are already taking opioid analgesics.

Fentanyl acts in the central nervous system (CNS) to relieve pain. Some of its side effects are also caused by actions in the CNS. When an opioid is used for a long time, it may become habit-forming or cause mental or physical dependence. However, under the close supervision of a healthcare provider, people who have continuous pain should not let the fear of dependence keep them from using opioids to relieve pain. Mental dependence (addiction) is less likely to occur when opioids are used for this purpose. Physical dependence may lead to withdrawal symptoms if treatment is stopped suddenly. Withdrawal symptoms can usually be prevented by gradually reducing the dose over a period of time before the medicine is stopped completely. Talk to your doctor about the benefits of this medicine and how to prevent withdrawal symptoms.

This medicine is available only under a restricted distribution program called the TIRF (Transmucosal Immediate Release Fentanyl) REMS (Risk Evaluation and Mitigation Strategy) program.

This product is available in the following dosage forms:

  • Spray
  • Tablet
  • Lozenge/Troche

Before Using

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For this medicine, the following should be considered:


Tell your doctor if you have ever had any unusual or allergic reaction to this medicine or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.


Appropriate studies have not been performed on the relationship of age to the effects of fentanyl in children younger than 18 years of age for the Abstral®, Fentora®, Onsolis®, and Subsys® brands, and in children younger than 16 years of age for the Actiq® brand. Safety and efficacy have not been established.


Appropriate studies performed to date have not demonstrated geriatric-specific problems that would limit the usefulness of fentanyl in the elderly. However, elderly patients may be more sensitive to the effects of opioid analgesics than younger adults and are more likely to have age-related lung or kidney problems, which may require caution and an adjustment in the dose for patients receiving fentanyl in order to avoid serious side effects.


There are no adequate studies in women for determining infant risk when using this medication during breastfeeding. Weigh the potential benefits against the potential risks before taking this medication while breastfeeding.

Drug Interactions

Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking this medicine, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

Using this medicine with any of the following medicines is not recommended. Your doctor may decide not to treat you with this medication or change some of the other medicines you take.

  • Levoketoconazole
  • Mifepristone
  • Nalmefene
  • Naltrexone
  • Safinamide
  • Samidorphan

Using this medicine with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

  • Abametapir
  • Acepromazine
  • Aclidinium
  • Adagrasib
  • Alefacept
  • Alfentanil
  • Almotriptan
  • Alprazolam
  • Amantadine
  • Amifampridine
  • Amiloride
  • Amineptine
  • Amiodarone
  • Amitriptyline
  • Amitriptylinoxide
  • Amobarbital
  • Amoxapine
  • Amphetamine
  • Amprenavir
  • Anileridine
  • Apalutamide
  • Aprepitant
  • Aripiprazole
  • Aripiprazole Lauroxil
  • Armodafinil
  • Asciminib
  • Asenapine
  • Atazanavir
  • Atropine
  • Avacopan
  • Baclofen
  • Belladonna
  • Belzutifan
  • Bemetizide
  • Bendroflumethiazide
  • Benperidol
  • Bentazepam
  • Benzhydrocodone
  • Benzphetamine
  • Benzthiazide
  • Benztropine
  • Berotralstat
  • Biperiden
  • Boceprevir
  • Bosentan
  • Bromazepam
  • Bromopride
  • Brompheniramine
  • Bumetanide
  • Buprenorphine
  • Bupropion
  • Buspirone
  • Butabarbital
  • Butorphanol
  • Calcium Oxybate
  • Cannabidiol
  • Cannabis
  • Canrenoate
  • Canrenone
  • Carbamazepine
  • Carbinoxamine
  • Carisoprodol
  • Carphenazine
  • Cenobamate
  • Ceritinib
  • Cetirizine
  • Chloral Hydrate
  • Chlordiazepoxide
  • Chlorothiazide
  • Chlorpheniramine
  • Chlorpromazine
  • Chlorthalidone
  • Chlorzoxazone
  • Cilostazol
  • Cimetidine
  • Ciprofloxacin
  • Citalopram
  • Clarithromycin
  • Clemastine
  • Clidinium
  • Clobazam
  • Clofazimine
  • Clomipramine
  • Clonazepam
  • Clopamide
  • Clopidogrel
  • Clorazepate
  • Cloxazolam
  • Clozapine
  • Cobicistat
  • Cocaine
  • Codeine
  • Conivaptan
  • Crizotinib
  • Cyclobenzaprine
  • Cyclopenthiazide
  • Cyclopentolate
  • Cyclosporine
  • Cyclothiazide
  • Cyproheptadine
  • Dabrafenib
  • Dantrolene
  • Daridorexant
  • Darifenacin
  • Darunavir
  • Delavirdine
  • Delorazepam
  • Desipramine
  • Desmopressin
  • Desvenlafaxine
  • Dexamethasone
  • Dexmedetomidine
  • Dextroamphetamine
  • Dextromethorphan
  • Dezocine
  • Diacetylmorphine
  • Diazepam
  • Diazoxide
  • Dibenzepin
  • Dichloralphenazone
  • Dicloxacillin
  • Dicyclomine
  • Difenoxin
  • Dihydrocodeine
  • Diltiazem
  • Dimenhydrinate
  • Diphenhydramine
  • Diphenoxylate
  • Dipyrone
  • Dolasetron
  • Donepezil
  • Doxepin
  • Doxylamine
  • Dronedarone
  • Droperidol
  • Duloxetine
  • Duvelisib
  • Efavirenz
  • Elagolix
  • Eletriptan
  • Enasidenib
  • Enflurane
  • Enzalutamide
  • Eplerenone
  • Erythromycin
  • Escitalopram
  • Esketamine
  • Eslicarbazepine Acetate
  • Estazolam
  • Eszopiclone
  • Ethacrynic Acid
  • Ethchlorvynol
  • Ethopropazine
  • Ethylmorphine
  • Etozolin
  • Etravirine
  • Fedratinib
  • Fenfluramine
  • Fesoterodine
  • Fexinidazole
  • Flavoxate
  • Flibanserin
  • Fluconazole
  • Flunitrazepam
  • Fluoxetine
  • Flurazepam
  • Fluspirilene
  • Fluvoxamine
  • Fosamprenavir
  • Fosaprepitant
  • Fosnetupitant
  • Fosphenytoin
  • Fospropofol
  • Frovatriptan
  • Furosemide
  • Gabapentin
  • Gabapentin Enacarbil
  • Gepirone
  • Glycopyrrolate
  • Glycopyrronium Tosylate
  • Granisetron
  • Halazepam
  • Haloperidol
  • Halothane
  • Hexobarbital
  • Homatropine
  • Hydrochlorothiazide
  • Hydrocodone
  • Hydroflumethiazide
  • Hydromorphone
  • Hydroxyamphetamine
  • Hydroxytryptophan
  • Hydroxyzine
  • Hyoscyamine
  • Idelalisib
  • Imatinib
  • Imipramine
  • Indapamide
  • Indinavir
  • Ipratropium
  • Isocarboxazid
  • Isoflurane
  • Itraconazole
  • Ivacaftor
  • Ivosidenib
  • Ketamine
  • Ketazolam
  • Ketobemidone
  • Ketoconazole
  • Lacosamide
  • Lanreotide
  • Larotrectinib
  • Lasmiditan
  • Lefamulin
  • Lemborexant
  • Lenacapavir
  • Lesinurad
  • Letermovir
  • Levocetirizine
  • Levomilnacipran
  • Levorphanol
  • Linezolid
  • Lisdexamfetamine
  • Lithium
  • Lofepramine
  • Lofexidine
  • Lomitapide
  • Lonafarnib
  • Loprazolam
  • Lorazepam
  • Lorcaserin
  • Lorlatinib
  • Lormetazepam
  • Loxapine
  • Lumacaftor
  • Magnesium Oxybate
  • Maribavir
  • Mavacamten
  • Mavorixafor
  • Meclizine
  • Medazepam
  • Melitracen
  • Melperone
  • Mepenzolate
  • Meperidine
  • Mephobarbital
  • Meprobamate
  • Meptazinol
  • Mesoridazine
  • Metaclazepam
  • Metaxalone
  • Methadone
  • Methamphetamine
  • Methdilazine
  • Methocarbamol
  • Methohexital
  • Methotrimeprazine
  • Methyclothiazide
  • Methylene Blue
  • Methylprednisolone
  • Metoclopramide
  • Metolazone
  • Midazolam
  • Milnacipran
  • Mirtazapine
  • Mitotane
  • Mobocertinib
  • Modafinil
  • Molindone
  • Moricizine
  • Morphine
  • Morphine Sulfate Liposome
  • Nafcillin
  • Nalbuphine
  • Naratriptan
  • Nefazodone
  • Nelfinavir
  • Netupitant
  • Nevirapine
  • Nicardipine
  • Nicomorphine
  • Nifedipine
  • Nilotinib
  • Nirmatrelvir
  • Nirogacestat
  • Nitrazepam
  • Nitrous Oxide
  • Nordazepam
  • Nortriptyline
  • Octreotide
  • Olanzapine
  • Oliceridine
  • Omaveloxolone
  • Ondansetron
  • Opipramol
  • Opium
  • Opium Alkaloids
  • Orphenadrine
  • Oxazepam
  • Oxcarbazepine
  • Oxitropium Bromide
  • Oxybutynin
  • Oxycodone
  • Oxymorphone
  • Ozanimod
  • Palbociclib
  • Palonosetron
  • Papaveretum
  • Paregoric
  • Paritaprevir
  • Paroxetine
  • Pazopanib
  • Pentazocine
  • Pentobarbital
  • Perampanel
  • Perazine
  • Periciazine
  • Perphenazine
  • Phenelzine
  • Phenobarbital
  • Phenytoin
  • Pimozide
  • Pinazepam
  • Pipenzolate Bromide
  • Piperacetazine
  • Pipotiazine
  • Pirenzepine
  • Piretanide
  • Piritramide
  • Pirtobrutinib
  • Polythiazide
  • Posaconazole
  • Potassium Oxybate
  • Prazepam
  • Prednisone
  • Pregabalin
  • Primidone
  • Procarbazine
  • Prochlorperazine
  • Procyclidine
  • Promazine
  • Promethazine
  • Propantheline
  • Propiverine
  • Propofol
  • Protriptyline
  • Quazepam
  • Quetiapine
  • Quinethazone
  • Ramelteon
  • Ranitidine
  • Ranolazine
  • Rasagiline
  • Remifentanil
  • Remimazolam
  • Remoxipride
  • Repotrectinib
  • Ribociclib
  • Rifabutin
  • Rifampin
  • Rifapentine
  • Ritlecitinib
  • Ritonavir
  • Rizatriptan
  • Ropeginterferon Alfa-2b-njft
  • Saquinavir
  • Schisandra sphenanthera
  • Scopolamine
  • Secobarbital
  • Selegiline
  • Selpercatinib
  • Sertindole
  • Sertraline
  • Sibutramine
  • Sodium Oxybate
  • Solifenacin
  • Sotorasib
  • Spironolactone
  • St John's Wort
  • Stramonium
  • Sufentanil
  • Sulpiride
  • Sumatriptan
  • Suvorexant
  • Tacrolimus
  • Tapentadol
  • Taurursodiol
  • Telaprevir
  • Telithromycin
  • Telotristat Ethyl
  • Temazepam
  • Terodiline
  • Tetrazepam
  • Thiethylperazine
  • Thiopental
  • Thiopropazate
  • Thioridazine
  • Tianeptine
  • Ticagrelor
  • Tilidine
  • Tiotropium
  • Tizanidine
  • Tocilizumab
  • Tolonium Chloride
  • Tolterodine
  • Topiramate
  • Torsemide
  • Tovorafenib
  • Tramadol
  • Tranylcypromine
  • Trazodone
  • Triamterene
  • Triazolam
  • Trichlormethiazide
  • Trifluoperazine
  • Trifluperidol
  • Triflupromazine
  • Trihexyphenidyl
  • Trimeprazine
  • Trimipramine
  • Trofinetide
  • Tropicamide
  • Trospium
  • Tryptophan
  • Tucatinib
  • Umeclidinium
  • Venlafaxine
  • Verapamil
  • Vilazodone
  • Vonoprazan
  • Voriconazole
  • Vortioxetine
  • Voxelotor
  • Xipamide
  • Zaleplon
  • Ziprasidone
  • Zolmitriptan
  • Zolpidem
  • Zopiclone
  • Zotepine
  • Zuranolone

Other Interactions

Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

Using this medicine with any of the following is usually not recommended, but may be unavoidable in some cases. If used together, your doctor may change the dose or how often you use this medicine, or give you special instructions about the use of food, alcohol, or tobacco.

  • Ethanol
  • Grapefruit Juice

Other Medical Problems

The presence of other medical problems may affect the use of this medicine. Make sure you tell your doctor if you have any other medical problems, especially:

  • Addison disease (adrenal gland problem) or
  • Alcohol use disorder, or history of or
  • Brain tumor, history of or
  • Breathing problems (eg, asthma, sleep apnea) or
  • Chronic obstructive pulmonary disease (COPD) or
  • Cor pulmonale (serious heart condition) or
  • Depression, history of or
  • Drug dependence, especially opioid use disorder, history of or
  • Head injury, history of or
  • Increased pressure in the head or
  • Mental health problems, history of—Use with caution. May cause side effects to become worse.
  • Bradyarrhythmia (slow heart rhythm) or
  • Hypotension (low blood pressure) or
  • Pancreatitis (inflammation of the pancreas) or
  • Seizures, history of—Use with caution. May make these conditions worse.
  • Diabetes—Use the Actiq® brand with caution. There are 2 grams of sugar in each unit.
  • Kidney disease or
  • Liver disease—Use with caution. The effects may be increased because of slower removal of the medicine from the body.
  • Asthma, acute or severe or
  • Short-term pain (eg, pain after surgery, headache, migraine, dental pain) or
  • Respiratory depression (serious breathing problem) or
  • Stomach or bowel blockage (including paralytic ileus), known or suspected—Should not be used in patients with these conditions.

Proper Use

Use this medicine only as directed by your doctor. Do not use more of it, do not use it more often, and do not use it for a longer time than your doctor ordered.

It is very important that you understand the rules of the TIRF REMS program to prevent addiction, abuse, and misuse of oxycodone. This medicine should also come with a Medication Guide. Read and follow these instructions carefully. Read it again each time you refill your prescription in case there is new information. Ask your doctor if you have any questions.

Use only the brand of this medicine that your doctor prescribed. Different brands may not work the same way.

Keep the medicine in the original blister package. Open the package right before use.

Abstral® tablets:

  • Place the tablet under your tongue until it dissolves. Do not chew, suck, or swallow the tablet.
  • Do not eat or drink anything until the tablet has dissolved. If your mouth is dry, use water to rinse your mouth before you place the tablet under your tongue.

Actiq® lozenges:

  • Place the medicine in your mouth between your cheeks and gums and actively suck on the medicine. Use the handle to move the lozenge around your mouth, especially along the inside of your cheeks. Twirl the handle often.
  • Do not bite or chew the lozenge.

Fentora® buccal tablets:

  • Peel the foil back on the blister pack to remove the tablet. Do not push the tablet through the foil on the blister pack because this may damage the tablet. Do not crush, split, chew, or swallow it.
  • Place the tablet between your upper gum and cheek, above a back molar tooth. You may instead place the tablet under your tongue, on the floor of your mouth.
  • When placing the tablet under your tongue, lift your tongue then place the tablet under it, and lower your tongue over the tablet.
  • The tablet should dissolve in 14 to 25 minutes. If the tablet does not dissolve completely after 30 minutes, you may drink a glass of water to help you swallow the left over medicine.

Onsolis® buccal film:

  • Use your tongue to wet the side of your cheek or rinse your mouth with water in the area where you will place the film.
  • Do not cut or tear the film. Hold the film on a clean, dry finger with the pink side facing up.
  • Press the film against your cheek and hold it there for 5 seconds.
  • Leave the film in place until it dissolves and do not touch or move the film. Do not chew or swallow the film.
  • If you must use more than one film, place the second film on the other side of your mouth.
  • Do not eat any food until the film dissolves. You may drink water or other liquids after 5 minutes.

Subsys® sublingual spray:

  • Carefully spray the medicine under your tongue.
  • Hold the medicine under your tongue for 30 to 60 seconds. Do not rinse your mouth and do not spit out any medicine.


The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

  • For cancer pain:
    • For buccal dosage form (film):
      • Adults—At first, one 200 microgram (mcg) film for each pain episode. Your doctor may adjust your dose as needed. However, the maximum number of pain episodes that can be treated each day is 4.
      • Children—Use and dose must be determined by your doctor.
    • For buccal dosage form (tablets):
      • Adults—At first, 100 micrograms (mcg) for each pain episode. If instructed by your doctor, this dose may be repeated after waiting 30 minutes between doses. Your doctor may adjust your dose as needed. However, the maximum number of pain episodes that can be treated each day is 4. Wait at least 4 hours before treating a new episode of pain.
      • Children—Use and dose must be determined by your doctor.
    • For transmucosal dosage form (lozenges):
      • Adults and children 16 years of age and older—At first, 200 micrograms (mcg) for each pain episode. If instructed by your doctor, this dose may be repeated after waiting 15 minutes between doses. Your doctor may adjust your dose as needed. However, the maximum number of units that can be used each day is 4. Wait at least 4 hours before treating a new episode of pain.
      • Children younger than 16 years of age—Use and dose must be determined by your doctor.
    • For sublingual dosage form (spray):
      • Adults—At first, 100 micrograms (mcg) or 1 spray for each pain episode. If instructed by your doctor, this dose may be repeated once after waiting 30 minutes. Additional pain episodes may be treated after a minimum of 4 hours.
      • Children—Use and dose must be determined by your doctor.
    • For sublingual dosage form (tablets):
      • Adults—At first, 100 micrograms (mcg) for each pain episode. If instructed by your doctor, this dose may be repeated after waiting 30 minutes between doses. Your doctor may adjust your dose as needed. However, the maximum number of pain episodes that can be treated each day is 4.
      • Children—Use and dose must be determined by your doctor.


Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.

Keep out of the reach of children.

Do not keep outdated medicine or medicine no longer needed.

Ask your healthcare professional how you should dispose of any medicine you do not use.

Abstral® tablets: If you have questions about the best way to dispose of the tablets you do not use, ask your pharmacist or call 1-888-227-8725.

Actiq® lozenges: If you have questions about the best way to dispose of the lozenges you do not use, ask your pharmacist or call 1-800-896-5855.

Fentora® tablets: If you have questions about the best way to dispose of the tablets you do not use, ask your pharmacist or call 1-800-896-5855.

Onsolis® film: If you have questions about the best way to dispose of the films you do not use, ask your pharmacist or call 1-800-526-3840.

Subsys® spray: Place the used spray unit into a disposal bag. Seal the disposal bag and throw it into a trash container that is out of the reach of children. For the unopened spray units, use the disposal bottle to empty the liquid from each unit. Place the disposal bottle in a bag and seal it. Throw the bag into a trash container that is out of the reach of children. If you have questions, call 1-877-978-2797.


It is very important that your doctor check your progress at regular visits. This will allow your doctor to see if the medicine is working properly and to decide if you should continue to take it.

Do not use this medicine if you are using or have used an MAO inhibitor (MAOI) (eg, isocarboxazid [Marplan®], linezolid [Zyvox®], phenelzine [Nardil®], selegiline [Eldepryl®], tranylcypromine [Parnate®]) within the past 14 days.

Using this medicine while you are pregnant may cause serious unwanted effects, including neonatal withdrawal syndrome in your newborn baby. Tell your doctor right away if you think you are pregnant or if you plan to become pregnant while using this medicine.

For nursing mothers taking this medicine:

  • Talk to your doctor if you have any questions about taking this medicine or about how it may affect your baby.
  • Call your doctor if you become extremely tired and have difficulty caring for your baby.
  • Your baby should generally nurse every 2 to 3 hours and should not sleep for more than 4 hours at a time.
  • Check with your doctor or hospital emergency room immediately if your baby shows signs of increased sleepiness (more than usual), difficulty breastfeeding, difficulty breathing, or limpness. These may be symptoms of an overdose and need immediate medical attention.

Fentanyl is a medicine that can harm or cause death to a child. Patients and caregivers should keep this medicine out of the reach of children. Carefully dispose of any partially used units or unused medicine properly.

This medicine may be habit-forming. If you feel that the medicine is not working as well, do not use more than your prescribed dose. Call your doctor for instructions.

This medicine may cause sleep-related breathing problems (eg, sleep apnea, sleep-related hypoxemia). Your doctor may decrease your dose if you have sleep apnea while using this medicine.

This medicine will add to the effects of alcohol and other CNS depressants. Some examples of CNS depressants are antihistamines or medicine for allergies or colds, sedatives, tranquilizers, or sleeping medicine, other prescription pain medicine or opioids, medicine for seizures or barbiturates, muscle relaxants, or anesthetics (numbing medicines), including some dental anesthetics. This effect may last for a few days after you stop using this medicine. Check with your doctor before taking any of these medicines while you are using this medicine.

Fentanyl may cause some people to become drowsy, confused, or dizzy. Make sure you know how you react to this medicine before you drive, use machines, or do anything else that could be dangerous if you are dizzy or not alert. Check with your doctor if you have confusion or drowsiness that is severe enough to interfere with your daily activities.

Using opioids for a long time can cause severe constipation. To prevent this, your doctor may tell you to take laxatives, drink fluids, or increase the amount of fiber in your diet. Follow the directions carefully. Constipation that continues can lead to more serious problems.

If you have been using this medicine regularly for several weeks or more, do not suddenly stop using it without checking with your doctor. You may be directed to gradually reduce the amount you are using before stopping it completely to lessen the chance of withdrawal symptoms.

If you think you have, or someone else has, taken an overdose of this medicine, get emergency help at once. Your healthcare provider may prescribe naloxone to treat an overdose. Naloxone is a medicine that can temporarily reverse the effects of an overdose. If you have been prescribed naloxone, or purchased it over-the-counter, make sure your household members know how to use it in the event of an overdose. Emergency help is still needed after naloxone is used because the reversal effects are only temporary. Signs of an overdose include: change or loss of consciousness, cold, clammy skin, coughing that sometimes produces a pink frothy sputum, decreased awareness or responsiveness, extreme dizziness or weakness, increased sweating, irregular, fast, or slow, or shallow breathing, pale or blue lips, fingernails, or skin, sleepiness or unusual drowsiness, slow heartbeat, seizures, swelling in legs and ankles, or trouble breathing. Call your doctor right away if you notice these symptoms.

The Actiq® product contains sugar and may increase your chance for tooth decay. Schedule regular dentist visits if you are using Actiq®.

Call your doctor right away if you have worsening of pain, increased sensitivity to pain, or new pain after taking this medicine. These may be symptoms of opioid-induced hyperalgesia and allodynia.

Check with your doctor right away if you have anxiety, restlessness, a fast heartbeat, fever, sweating, muscle spasms, twitching, nausea, vomiting, diarrhea, or see or hear things that are not there. These may be symptoms of a serious condition called serotonin syndrome. Your risk may be higher if you also take certain other medicines that affect serotonin levels in your body.

This medicine may cause adrenal gland problems. Check with your doctor right away if you have darkening of the skin, diarrhea, dizziness, fainting, loss of appetite, mental depression, nausea, skin rash, unusual tiredness or weakness, or vomiting.

Dizziness, lightheadedness, or fainting may occur when you get up suddenly from a lying or sitting position. Getting up slowly may help lessen this problem. Also, lying down for a while may relieve dizziness or lightheadedness.

Using too much of this medicine may cause infertility (unable to have children). Talk with your doctor before using this medicine if you plan to have children.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal (eg, St. John's wort) or vitamin supplements.

Side Effects

Along with its needed effects, a medicine 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:

More common

  1. Black, tarry stools
  2. blurred vision
  3. chest pain or tightness
  4. confusion
  5. cough
  6. decreased urine
  7. difficult or labored breathing
  8. dizziness
  9. dry mouth
  10. fainting
  11. fever or chills
  12. increased thirst
  13. irregular heartbeat
  14. lightheadedness
  15. loss of appetite
  16. lower back or side pain
  17. mood changes
  18. muscle pain or cramps
  19. nausea or vomiting
  20. nervousness
  21. numbness or tingling in the hands, feet, or lips
  22. painful or difficult urination
  23. pale skin
  24. pounding in the ears
  25. rapid breathing
  26. seizures
  27. sneezing
  28. sore throat
  29. sunken eyes
  30. swelling of the hands, ankles, feet, or lower legs
  31. trouble breathing with exertion
  32. ulcers, sores, or white spots in the mouth
  33. unusual bleeding or bruising
  34. unusual tiredness or weakness
  35. wrinkled skin

Less common

  1. Change in walking and balance
  2. clumsiness or unsteadiness
  3. decreased awareness or responsiveness
  4. decreased frequency of urination
  5. headache
  6. muscle twitching or jerking
  7. pounding in the ears
  8. rhythmic movement of the muscles
  9. seeing, hearing, or feeling things that are not there
  10. severe constipation
  11. severe sleepiness
  12. shakiness in the legs, arms, hands, or feet
  13. slow or fast heartbeat
  14. stomach pain
  15. thinking abnormalities
  16. trembling or shaking of the hands or feet

Incidence not known

  1. Increased sensitivity to pain
  2. worsening of pain

Get emergency help immediately if any of the following symptoms of overdose occur:

Symptoms of overdose

  1. Extremely shallow or slow breathing

Some side effects 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

  1. Back pain
  2. diarrhea
  3. difficulty having a bowel movement (stool)
  4. difficulty with moving
  5. discouragement
  6. feeling sad or empty
  7. irritability
  8. lack or loss of strength
  9. loss of interest or pleasure
  10. muscle stiffness
  11. pain in the joints
  12. sleepiness or unusual drowsiness
  13. tiredness
  14. trouble concentrating
  15. trouble sleeping
  16. weight loss

Less common

  1. Changes in vision
  2. excessive muscle tone
  3. feeling of constant movement of self or surroundings
  4. feeling of warmth or heat
  5. flushing or redness of the skin, especially on the face and neck
  6. irritation, pain, or sores at the site of application
  7. itching skin
  8. muscle tension or tightness
  9. rash
  10. sensation of spinning
  11. sweating

Incidence not known

  1. Tooth pain
  2. trouble with gums
  3. trouble with teeth

Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.

Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.