Flexeril side effects and drug information

Flexeril is a brand name and a kind of medication that is used to aid in relaxing specific muscles in the body. This medicine is available as well in a generic form which is called cyclobenzaprine.


ChemSpider ID

Protein binding93%
CAS ID303-53-7
Molar mass275.387 g/mol


This was formulated to help in relieving pain, stiffness, and other discomforts that are caused by strains, sprains, or injuries to the muscles. Though it offers relief for these types of muscle pains or strains, this medicine still is no match for rest, exercise, and physical therapy.

Flexeril or cyclobenzaprine works on the central nervous system to produce its muscle relaxant effects. However, though it functions on the central nervous system, it may also be the root or trigger for the side effects.

This muscle relaxant medication may be used as part of combination therapy.

How It Works

Flexeril comes from a class of drugs called muscle relaxants. These types of drugs work to relieve pain, stiffness, and other discomforts in certain muscles. Though, it is not precisely known how this medication functions in relaxing the muscle. 

Cyclobenzaprine may also tend to decrease the signals from the brain that instructs your muscles to cause spasm.

Side Effects

As in any other drugs, this muscle relaxant may also potentially cause some side effects to its users, which can either be some common side effects or serious ones depending on the body’s reaction and the person’s condition.

It is said that its oral tablet form may trigger dizziness and drowsiness, which may occur more likely after a few hours from taking it.

Some of the more common side effects, as well as its serious side effects, will be mentioned here.

Common Side Effects

Serious Side Effects

For the symptoms in relation to heart problems, the person may experience the following:

  • Fainting
  • Heart palpitations
  • Confusion
  • Trouble speaking or understanding
  • Loss of control or numbness in the face, arms or legs
  • Trouble seeing in 1 or both eyes

For the symptoms involving serotonin syndrome, the user may experience:

  • Agitation
  • Hallucinations
  • Seizures
  • Nausea

Indication and dosage

The following information on the average dose for this medication is for its oral tablet version. Medicine dosage, drug form, and how often you take a drug may vary according to different factors such as:

  • Patient’s age
  • The user’s condition that is being treated
  • How severe the patient’s condition is
  • If the individual has other medical conditions
  • How the person’s body reacts to the first dose

Forms and strengths of this medication in its generic and brand name versions:

The generic name is cyclobenzaprine, and it comes in an oral tablet form. It is available in 5mg, 7.5mg, and 10mg strengths

For the brand name version, the drug is called Fexmid, and it is also available in oral tablet form. It comes in 1 strength, which is 7.5mg.

The dosage for muscle spasm relief are the following:

  • For the adult dose, which is for ages 18 to 64 years old, this medicine with 5 to 10mg strength must be taken three times a day.
  • For the child dose, which is designed for 15 to 17 years old, they may take 5 to 10mg strength three times per day.
  • For children 0 to 14 years old, this medicine is not recommended for them as this should not be used for those who are younger than 15 years old.

For the seniors with ages from 65 years old and up, since their kidneys do not function properly as they used to, their bodies may process the drug more slowly which will then cause the drugs to stay in the body for a much longer time, and might lead to an increased risk of side effects. Because of this reason, the doctor may either lower their dosage or give a different dosing schedule so that the drugs will be prevented from building up too much in the body.

Special Dosage Considerations

The special and appropriate dosage is given for individuals who have issues in the liver. If the person’s liver problem is mild, the doctor may adjust and provide a lower dosage or may give a different dosing schedule. But if the liver problem is either moderate or severe, do not take this drug as it may cause further complications.

Drug Interaction

This medication may also have the potential to interact with other drugs, which includes vitamins and herbal medicines. To avoid drug interactions, it is better to consult with your doctor and inform you about all your other medications so that he or she can manage your medicines carefully.  

Interactions that increase your risk of side effects

There are some types of drugs that may give you an increased risk of experiencing side effects when you take cyclobenzaprine. The reason for this is because the amount of cyclobenzaprine is increased in your body.

The following drugs may cause an increased risk for side effects:

  • Benzodiazepines such as triazolam, alprazolam, and midazolam. Taking this type of drug along with cyclobenzaprine may lead to increased drowsiness and sedation
  • Barbiturates such as phenobarbital
  • Drugs used as a treatment for depression like fluoxetine, venlafaxine, amitriptyline, or bupropion. When you take any of these with cyclobenzaprine, you may be at a higher risk for serotonin syndrome.
  • Verapamil
  • Anticholinergic drugs such as tolterodine or oxybutynin. This may interact with cyclobenzaprine and give a higher risk for side effects like dry mouth and unable to urinate.

Interactions that can make your drug less effective

Cyclobenzaprine may also change how certain drugs function, which may result in medicine not working correctly. An example of this is guanethidine. When this is used along with cyclobenzaprine, its blood pressure- lowering effects may be hindered and may lead to an increase in blood pressure.

Warnings and Precautions

It is always important to check product labels before usage to know the appropriate dosage and the possible side effects of the medicine. Or to ensure safety, consult with your doctor first and inform him or her if you are allergic to the medication, or if you have any other allergies as the drug may have some inactive components and may cause allergic reactions.

It is also best to inform your healthcare provider about your medical history, most especially when you have these types of conditions: liver disease, overactive thyroid, heart problems, difficulty urinating, or glaucoma.

This medicine may cause drowsiness or dizziness as well, so if you are taking this product, avoid driving or operating machinery.  

The use of cyclobenzaprine is also not advisable to be taken along with alcohol or cannabis, as it may make you feel dizzier.

Prior to surgery, it is best to also inform your doctor or dentist about all your other medicines, including prescription, nonprescription, herbal, etc. 

Older adults may have more sensitivity to experiencing side effects from this medicine, such as drowsiness, confusion, constipation, or trouble urinating. Drowsiness can be dangerous for older people as it may increase their risk of falling.

Important Warnings

Some more important warnings that people using this product should know about:

Serotonin syndrome warning

This drug may result in a life-threatening condition known as serotonin syndrome. This occurs when medicines cause too much serotonin to build up in the body. Users of this drug should watch out for these symptoms of agitation, hallucinations, seizures, or nausea. The risk becomes higher if you take cyclobenzaprine along with other medicines such as antidepressants.

Effects on the heart warning

This type of medication may cause heart arrhythmias such as heart rate or rhythm problems, and the risk becomes greater if you have heart problems or if you are taking anti-depression drugs with it. If heart problems are not treated, it may lead to a heart attack or stroke.

Central nervous system warning

The use of cyclobenzaprine may cause drowsiness, hallucinations, dizziness or delusions, so if you are under this treatment, avoid driving or using machinery. The greater risk is for those who are 65 years old and up.

Overdose and Contraindications

It is advised that cyclobenzaprine should not be taken along with monoamine oxidase inhibitors or MAOIs such as selegiline, rasagiline, and tranylcypromine as it may lead to some harmful effects to the body. 

Also important to note is that taking cyclobenzaprine with MAOI or within 14 days of stopping an MAOI may cause an increased risk of some serious side effects like seizures.

Clinical Pharmacology

Cyclobenzaprine is a prescription drug that is also available in its brand name version called Fexmid. Though it also comes in a generic brand, the efficacy or the strength may not be the same as the one with the brand name even if it is less expensive. This drug is also available as an oral extended-release capsule.

Medication Guide


  • This medication may be consumed with or without food
  • It can be taken about the same time each day
  • You are allowed to cut or crush the tablet

Since not all pharmacies stock this product, call ahead when refilling your prescription.


  • This product must be stored at 25°C 
  • Should be kept away from light
  • Do not store in moist or damp areas

This prescription is refillable, but you do not need a new prescription for every refill as the doctor will write the number of refills authorized for this.


 The drug is used to cure and prevent osteoporosis among sufferers. It is likewise used among patients with Paget’s disease.

What is Alendronate?

Alendronate is an oral medicine that is available as a tablet, effervescent tablet, and oral solution. The medication is available as a branded drug under the name Binosto and Fosamax. It is also sold as a generic drug. Alendronate is used to cure osteoporosis and Paget’s disease among patients.

Usage of Alendronate

Alendronate is utilized to cure and treat osteoporosis. With this, your bones can turn weak and thin and easily break. The medicine can also cure Paget’s disease. In this ailment, the bones can become weak and soft, and eventually, it can become painful and all deformed as well as break easily. Alendronate is a valuable part of any combination therapy, which is potent when coupled with Vitamin D and Calcium supplements.

Alendronate – How It Works

Alendronate is a part of a class of drugs widely known as Bisphosphonates. It is a type of medicine that is a class of medications that work in the same way for muscle cramps. The drugs are used to treat osteoporosis and Paget’s disease. Alendronate works by inhibiting the sudden thinning and breakdown of the bone. This helps improve bone density and helps the bones stay strong and avoid breaking.

Side Effects

The most common Alendronate side effects are as follows:

If the effects are rather mild, they can go away quickly in a couple of days or weeks. But, if the symptoms are rather severe, or where they are severe, contact your doctor right away.

Alendronate Serious Side Effects

Contact your physician or pharmacist immediately if you experience any of the following serious side effects. Call for emergency medical assistance if you experience any life-threatening symptoms. The serious side effects of Alendronate are as follows:

Erosions or ulcers of the esophagus, the symptoms are as follows:

  • Problem swallowing
  • Heartburns
  • Pain when swallowing
  • Chest pain 
  • Bloody vomit
  • Bloody stools

Bone death of jaw. Here are the symptoms:

  • Loosen teeth
  • Swollen gums
  • Poor healing of the jaw
  • Heavy feeling in the jaw

Unusual breaking of bones in the legs and hips. It can include:

  • Dull pain in the hips
  • Pain in the groin
  • Pain in the thigh area

Hypocalcemia or Low Calcium. The symptoms are:

  • Numb fingers
  • Numb toes
  • Numbness in the mouth area
  • Muscle cramps
  • Severe joint pains

Dosage and Administration

The dosage information provided here is for the Alendronate tablet. The dosages and drug form may not be added here. The dosage, drug type, and how often the drug is taken will depend on the patients:

  •  Age
  • Condition treated
  • Severity of condition
  • Other medical conditions
  • How the patient reacts to the first dose

Dosage for Osteoporosis

Alendronate Tablet

  •  Tablet
  •  Variants of 5mg, 10mg, 35mg, 40mg, and 70mg

Alendronate Oral Solution

  • 70mg/75ml

Fosamax Tablet

  • Tablet
  • 70 mg strength

Binosto Effervescent Tablet

  • 70 mg strength

Adult Dosage (18 years and older)

  • 70 milligrams once a week or 10 milligrams once a day for treatment
  • 35 milligrams once a week or 5 milligrams once a day

Child Dosage (0–17 years old)

  • The drug should not be used by individuals who are 18 years old and younger.


Different medications require different storage requirements. Always read the product label found on the packaging on how to properly store your Alendronate medication. Keep your medication away from pets and children’s reach at all times.

Never flush out your medication down the toilet or the drain unless when you are told to do so. Follow proper ways of discarding your medication found on the product packaging when no longer in need or when the product expires. Ask your doctor or pharmacist for proper waste disposal.

Drug Interaction

Alendronate tablet interacts with other medications, vitamins, or herbal supplements. The interaction occurs when a substance changes the way the medicine works. This can be dangerous and hinder the medicines from working well. To avoid any interactions, the physician will manage your medications. Make sure you inform your doctor about all the vitamins, supplements, and medicines you are taking. Check how the drug can interact with something you are taking.

Here are the drugs that can result in interactions with the Alendronate drug.

Interactions that can heighten side effects:

Taking Alendronate tablet with some drugs can result in more side effects, here is the list of these drugs:

  • Aspirin
  • NSAIDs or non-steroidal anti-inflammatory drugs

You can have more upper gastrointestinal side effects like ulcers in our esophagus area. Ask the physician if it is safe for you to take these drugs.

Interactions can make the drug Alendronate less effective. Whenever used with some drugs, it cannot work well to treat your condition. Alendronate in the body can be decreased. Here are some drugs:

  • Iron
  • Magnesium
  • Calcium supplements
  • Antacids

The drugs mentioned above can reduce how the medication absorbs in the body. You should let at least 30 minutes to pass after taking your alendronate another oral medication.

Warnings and Precautions

Food Warning

Take this drug on an empty stomach with a glass of water. Never take with coffee, tea, juice, soda, or mineral water. Doing so can minimize the level of the drug’s potency in the body. It can also heighten certain side effects. Wait at least 30 minuted before you eat or drink something.

Alcohol Warning

Alcohol can heighten the risk of some side effects on your stomach from taking alendronate. When you intend to drink alcohol, ask your doctor first about it. They can monitor and assess your stomach problems.

Allergy warning

The medication alendronate can lead to some very severe allergic reactions. Symptoms of its side effects can include:

  • Skin rashes
  • Hives
  • Swollen face
  • Swollen lips
  • Swollen tongue
  • Problems breathing

Whenever you experience any allergic reaction, call your doctor or the local poison center in your area without delay. When the symptoms you experience are rather severe, call for emergency medical assistance or dial 911. Never attempt to take this medication ever again if you have ever had any allergic reactions to the drug. Taking it once again can be dangerous and can even lead to death.

Warnings for Certain Users

For those with problems in their esophagus, never take this medication. You will be more likely to have severe side effects like erosions or ulcers in the esophagus area.

For patients with very low calcium blood levels, the physician must provide you calcium medications before starting to take this medicine. Taking Alendronate can only make your health condition worse.

For patients with severe kidney problems, well for those with kidney problems or a history of kidney ailment, you should not be able to clear this from your body. So, you should avoid taking Alendronate altogether.

Pregnant Women

For pregnant women, Alendronate is a regulated category C pregnancy drug. It can only mean two things:

  • There are no enough studies made on humans to be sure how Alendronate can impact the unborn child.
  • The research revealed that in animals, adverse effects occur to the fetus when the mother took the medication.

Always make sure to ask your doctor if you intend to become pregnant or already pregnant. The Alendronate can be used when the potential advantage justifies the risk to the unborn child.

Those who are breastfeeding must consult with their doctor first if they can use Alendronate while breastfeeding. It is not known whether Alendronate can pass into breast milk. When it does, it can lead to some serious side effects to the nursing baby. Ask your doctor or pharmacist if you are breastfeeding a baby and intend to take the medication. They will decide whether you should stop taking the medication altogether.

Senior citizen patients who have kidney problems or who have weakened kidneys must not take Alendronate too. This medication can lead the body to process certain medicines very slowly. This can result in other problems as the drug will stay in the body for an extended period, and it raises your risk to other side effects.

Pediatric patients are refrained from using this medication. It is not for use by patients 18 years old and below.

Overdose and Contraindications

When someone you know has overdosed or has severe symptoms like trouble breathing, passing out, or more, call a doctor or pharmacist for immediate medical assistance. You can also call on the poison control center immediately. Residents from the USA can call on their local poison control center for assistance. Severe symptoms of overdose can include persistent nausea, vomiting, diarrhea, stomach pain, or cramps. Never share this medication with another person even if they have symptoms similar to you.

The drug has been prescribed for your condition only. Never take any other pain reliever for your urinary tract problem unless you have consulted with your doctor. A different drug may be needed under this circumstance.