If you have trouble falling asleep or staying asleep, your doctor might suggest Belsomra as a treatment option. It’s a prescription drug prescribed to help treat insomnia (trouble sleeping) in adults. Your doctor may prescribe Belsomra for short-term or long-term treatment.

Belsomra comes as a tablet that you swallow. It contains the active ingredient suvorexant. (An active ingredient is what makes a drug work.)

For more information about Belsomra, including details about its uses, see this in-depth article.

Like other drugs, Belsomra can cause mild to serious side effects. Keep reading to learn more.

Some people may experience mild to serious side effects during their Belsomra treatment.

Examples of the drug’s commonly reported side effects include:

* To learn more about this side effect, see the “Side effects explained” section below.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. If you’d like to notify the FDA about a side effect you’ve had with Belsomra, visit MedWatch.

Many of Belsomra’s common side effects are mild and don’t require medical attention.

Examples of mild side effects that have been reported with this drug include:

* To learn more about this side effect, see the “Side effects explained” section below.

In most cases, these side effects should be temporary. And some may be easily managed. But if you have symptoms that are ongoing or bother you, talk with your doctor or pharmacist. And do not stop taking Belsomra unless your doctor recommends it.

Belsomra may cause mild side effects other than those listed above. See the drug’s prescribing information for details.

Although rare, some people may have serious side effects from Belsomra.

Serious side effects that have been reported with this drug include:

If you develop serious side effects while taking Belsomra, call your doctor right away. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911 or your local emergency number.

* To learn more about this side effect, see the “Side effects explained” section below.
† An allergic reaction is possible after taking Belsomra, but this side effect wasn’t reported in studies.

Help is out there

If you or someone you know is in crisis and considering suicide or self-harm, please seek support:

If you’re calling on behalf of someone else, stay with them until help arrives. You may remove weapons or substances that can cause harm if you can do so safely.

If you are not in the same household, stay on the phone with them until help arrives.

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Get answers to some frequently asked questions about Belsomra’s side effects.

Does the Belsomra drugmaker provide side effect reviews?

No, Belsomra’s drugmaker doesn’t provide reviews about the drug’s side effects. If you have questions about side effect reviews of Belsomra, talk with your doctor.

Can Belsomra cause weight gain or weight loss?

It shouldn’t. Weight gain and weight loss weren’t reported in the drug’s studies.

One small study looked at the effects of suvorexant* on blood pressure, body weight, and certain lab tests. The study found that people had weight gain after taking the drug for 10 months. But the study was too small to know whether the medication was the actual cause of the weight gain.

Talk with your doctor if you have concerns about weight changes while taking Belsomra.

* Suvorexant is the active ingredient in Belsomra. (An active ingredient is what makes a drug work.)

Is Belsomra safe to take?

Whether Belsomra is safe for you to take may depend on several factors. These can include:

  • other drugs you take
  • your age
  • other conditions you have

Like all drugs, Belsomra may have side effects, though many of its common side effects are mild and temporary. Still, it’s possible to have serious side effects from this drug.

To learn whether Belsomra is safe for you, talk with your doctor about your specific health conditions and the medications you take. Your doctor will help you decide if this is the right treatment option for you.

How do the side effects of Belsomra 10 mg compare with those of other strengths?

Belsomra tablets come in four strengths:

  • 5 milligrams (mg)
  • 10 mg
  • 15 mg
  • 20 mg

In the drug’s studies, many side effects were the same in people taking the 10-mg dose as in those taking 20 mg. But certain side effects, such as daytime sleepiness and increased cholesterol levels, were more common with higher doses.

Talk with your doctor if you have questions about side effects of your Belsomra dosage.

Do older adults experience different side effects from Belsomra?

It’s possible. In Belsomra’s studies, many side effects were the same in older adults (ages 65 years and above) as in younger adults. But the risk of certain side effects, such as excessive sleepiness and dizziness, may be higher in older adults.

Keep in mind that sleepiness during the day was the most common side effect reported in Belsomra’s studies. And excessive sleepiness can increase the risk of falls in older adults.

Talk with your doctor if you have concerns about the risks of this drug’s side effects based on your age.

Learn more about some of the side effects Belsomra may cause.

Unusual sleep behaviors

Unusual sleep behaviors have been reported by people taking Belsomra. This can include performing certain activities while not fully awake. Usually, people don’t remember having done these activities the following day.

Some of these reported activities include:

  • sleepwalking
  • driving a vehicle
  • preparing and eating food
  • making phone calls
  • having sex

These behaviors can happen after your first Belsomra dose or at any time during your treatment. And they can occur whether or not you’ve taken other sleep medications.

What might help

Some unusual sleep behaviors could be dangerous and lead to injuries or serious accidents. If you or someone else in your household notices that you have unusual sleep behaviors while taking this drug, let your doctor know right away. They’ll likely have you stop taking Belsomra and recommend a different treatment option.

Excessive sleepiness and decreased alertness

Taking Belsomra can cause excessive sleepiness and decreased alertness the day after you take it. In fact, this was the most common side effect in the drug’s studies. And it was more common in females* than in males.*

Belsomra can cause central nervous system (CNS) depression. This means the drug slows down your brain activity, which can reduce your ability to think clearly and react quickly. It also causes sleepiness.

The risk of these side effects is higher if you take higher doses of Belsomra or if you take other CNS depressants with this drug. Examples of other CNS depressants include:

* In this article, we use the terms “female” and “male” to refer to someone’s sex assigned at birth. For information about the difference between sex and gender, see this article.

What might help

It’s important to allow at least 7 hours to devote to sleep after taking Belsomra. This can reduce your risk of excessive sleepiness and decreased alertness the next day.

Be sure to tell your doctor about all the medications you take before starting Belsomra. If you take drugs that increase your risk of excessive sleepiness and decreased alertness, your doctor may recommend a different treatment than Belsomra.

They’ll also recommend that you avoid drinking alcohol while taking this drug.

If your doctor prescribes a higher dose of Belsomra, such as 20 milligrams (mg), they’ll likely recommend you do not drive the next day or perform activities that require full alertness. This is just until you know how your body reacts to the drug.

Sleep paralysis

It’s possible to have sleep paralysis while taking Belsomra. This is a rare side effect reported in the drug’s studies. With sleep paralysis, you may not be able to move or speak for a few minutes while you transition from sleep to wakefulness. The risk of this side effect is increased with higher doses of the drug.

What might help

Before you start taking Belsomra, your doctor will discuss the risk of sleep paralysis with you. Let them know if you experience this side effect during your Belsomra treatment. They may lower your dose or have you stop taking this drug.

Allergic reaction

Like most drugs, Belsomra can cause an allergic reaction in some people. But this side effect wasn’t reported in studies.

Symptoms can be mild to serious and can include:

  • skin rash
  • itchiness
  • flushing (temporary warmth, redness, or deepening of skin color)
  • swelling under your skin, usually in your eyelids, lips, hands, or feet
  • swelling of your mouth, tongue, or throat, which can make it hard to breathe

What might help

If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. They may suggest a treatment to manage your symptoms. Examples include:

  • an antihistamine you swallow, such as Benadryl (diphenhydramine)
  • a product you apply to your skin, such as hydrocortisone cream

If your doctor confirms you’ve had a mild allergic reaction to Belsomra, they’ll decide whether you should continue taking it.

If you have symptoms of a severe allergic reaction, such as swelling or trouble breathing, call 911 or your local emergency number right away. These symptoms could be life threatening and require immediate medical care.

If your doctor confirms you’ve had a serious allergic reaction to Belsomra, they may have you switch to a different treatment.

Keeping track of side effects

During your Belsomra treatment, consider taking notes on any side effects you’re having. You can then share this information with your doctor. This is especially helpful when you first start taking a new drug or using a combination of treatments.

Your side effect notes can include things such as:

  • what dose of the drug you were taking when you had the side effect
  • how soon you had the side effect after starting that dose
  • what your symptoms were
  • how your symptoms affected your daily activities
  • what other medications you were taking
  • any other information you feel is important

Keeping notes and sharing them with your doctor will help them learn more about how Belsomra affects you. They can then use this information to adjust your treatment plan if needed.

Belsomra may not be right for you if you have certain medical conditions. This is known as a drug-condition interaction. Other factors may also affect whether this drug is a good treatment option for you. Talk with your doctor about your health history before starting Belsomra. Factors to consider include those described below.

Depression or other mental health conditions. Belsomra can worsen depression or increase the risk of suicidal thoughts and behavior. Tell your doctor if you have depression or other mental health conditions before starting this drug. They may recommend a different treatment option for you. If they do prescribe Belsomra, they’ll monitor you closely for worsening depression or suicidal thoughts and behaviors.

Allergic reaction. If you’ve had an allergic reaction to Belsomra or any of its ingredients, your doctor will likely not prescribe it for you. Ask them about other medications that might be better options for you.

Breathing problems. Belsomra can cause cough and upper respiratory tract infection. These side effects can irritate your lungs. If you already have breathing problems, such as chronic obstructive pulmonary disease (COPD), this drug may worsen them. Talk with your doctor about your health history before starting Belsomra. They’ll help you decide whether this treatment option is right for you.

Narcolepsy. Belsomra can cause daytime sleepiness and worsen narcolepsy. It can also make certain drugs prescribed to treat narcolepsy less effective. Tell your doctor if you have this condition before taking Belsomra. They’ll likely not prescribe this medication for you.

History of substance or alcohol misuse. Belsomra is a controlled substance in the United States and has the potential for misuse. (See the “Belsomra and Misuse” section below for more information.) If you have a history of substance or alcohol misuse, Belsomra may not be the right option for you. Talk with your doctor to learn about safe treatments for your insomnia (trouble sleeping).

Liver problems. It’s not known whether it’s safe to take Belsomra if you have severe liver problems. Let your doctor know if you have liver problems before starting this drug. They’ll check your liver function to determine whether this medication is safe for you.

Older adults. If you’re age 65 years or over, your risk of certain side effects from Belsomra may be higher. These include drowsiness and dizziness, which may lead to falls. Due to this risk, your doctor will likely prescribe a lower dosage of Belsomra if you’re age 65 years or over.

Cataplexy. In rare cases, Belsomra can cause cataplexy (sudden muscle weakness). If you already have this condition, your risk may be higher. Tell your doctor if you’ve ever experienced cataplexy before starting Belsomra treatment. They’ll help you decide whether this medication is right for you.

Alcohol and Belsomra

You should not drink alcohol while taking Belsomra. This is because they’re both central nervous system depressants, which means they can slow down your brain activity. Consuming alcohol with Belsomra can increase your risk of side effects such as:

If you drink alcohol during your Belsomra treatment, you should not take Belsomra that evening before you go to bed.

Talk with your doctor if you have questions about alcohol consumption with Belsomra.

Pregnancy and breastfeeding while taking Belsomra

It’s not known whether it’s safe to take Belsomra during pregnancy. If you’re pregnant or planning to become pregnant, let your doctor know before you start taking this drug. They’ll likely recommend a different treatment for your insomnia.

It’s also not known whether Belsomra passes into breast milk or the effects it could have on a child who is breastfed. Tell your doctor if you’re breastfeeding or planning to do so before starting this drug. They may recommend a different treatment for your condition.

Belsomra contains the active ingredient* suvorexant, which is a controlled substance. This means the drug has the potential for misuse. (Misuse is when a drug is taken or used differently than how your doctor prescribes it.) It also means that government agencies, doctors, and pharmacists pay close attention to how the drug is prescribed and used.

The following factors can increase the risk of Belsomra misuse:

  • having a history of substance or alcohol misuse
  • taking Belsomra with alcohol or other misused drugs
  • taking Belsomra long term

Misusing Belsomra increases your risk of:

  • excessive daytime sleepiness
  • slowed reaction time
  • impaired driving skills

Belsomra is a Schedule IV controlled substance, which means it carries a low risk of misuse or dependence. (Dependence is when your body gets used to a drug and needs it for you to function as usual.)

Even though the risk of misuse is low, doctors will closely monitor people with a history of alcohol or substance misuse who are taking Belsomra.

* An active ingredient is what makes a drug work.

Many side effects of Belsomra are mild and temporary, but the drug may cause serious side effects in rare cases. It’s important to talk with your doctor before you start taking Belsomra. They can help answer questions you may have about the drug’s side effects.

Examples of questions you may want to ask include:

  • Can Belsomra cause anxiety?
  • Does my risk of headache depend on the dosage I take?
  • How do the side effects of Belsomra compare with those of Dayvigo (lemborexant)?

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Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.