Introduction

If you’re looking for a medication to help you fall asleep, you likely don’t want to end up with lots of side effects. ZzzQuil Nighttime Sleep-Aid is an over-the-counter (OTC) medication that can help relieve occasional sleep problems. Here’s what you need to know about ZzzQuil’s possible side effects and how to manage them, when possible.

Digestive system effects

Because you take ZzzQuil by mouth, it goes through your digestive system. As a result, it may cause mild stomach upset. Digestive side effects can include the following:

  • loss of appetite
  • nausea
  • vomiting
  • constipation

If these side effects bother you, or if they get worse or don’t go away, call your doctor. To reduce stomach upset, try taking ZzzQuil with food or milk.

Nervous system effects

ZzzQuil can cause side effects to the nervous system, which includes your brain and spinal cord. Call your doctor if mild side effects bother you, get worse, or don’t go away. These side effects can include the following:

  • drowsiness
  • dizziness
  • headache
  • muscle weakness
  • excitement (especially in children)

More serious side effects can occur if you overdose on this medication. Call your doctor right away if you have any serious side effects, which can include:

  • severe drowsiness or sleepiness
  • nervousness
  • agitation
  • confusion
  • tremors
  • feeling unsteady (such as while walking)
  • seizures
  • hallucinations (seeing or hearing things that aren’t real)
  • delirium (severe confusion)
  • coma

Respiratory system effects

ZzzQuil can cause some symptoms in your respiratory system, or the parts of your body you use to breathe. Call your doctor if any of these side effects bother you, get worse, or don’t go away. They can include:

  • congestion in your chest
  • dryness of your throat, mouth, or nose

To reduce these side effects, try drinking more water. If your diet restricts fluids, talk to your doctor before increasing your water intake.

Cardiovascular system effects

ZzzQuil can affect your heart and blood vessels. Serious side effects can occur if you take too much. Call your doctor right away if you have any serious side effects. These can include:

  • dangerously low blood pressure, which can cause lightheadedness
  • very fast heart rate
  • palpitations (skipped heartbeats)
  • arrhythmia (irregular heart rhythm)

If you feel lightheaded while taking this medication, be sure to sit or lie down. This can help prevent injury in case you pass out.

Vision and hearing effects

ZzzQuil can affect your eyes and ears. If you take too much, you may have serious side effects, such as:

  • eye and vision problems, such as blurry vision and extremely dry eyes
  • ringing in your ears

If you have dry eyes from this medication, try using artificial tears to moisten them. You should call your doctor if you notice any effects on your vision or hearing while you take ZzzQuil.

Urinary system effects

ZzzQuil can negatively affect your urinary system if you take too much. Call your doctor right away if you have any urinary side effects, which can include:

  • trouble urinating
  • pain when urinating

How ZzzQuil causes side effects

When you take ZzzQuil at bedtime, it can help you fall asleep more easily. This is because it contains a drug called diphenhydramine. This drug works by blocking histamine receptors in your brain. Histamine is a chemical that helps control alertness in the brain. So, when ZzzQuil blocks your histamine receptors, it causes drowsiness to help you sleep. ZzzQuil can also block acetylcholine receptors. Acetylcholine is a natural chemical that affects many functions in your body, including your heart rate, muscle movement, memory, and attention.

When ZzzQuil is used as directed, side effects are not common. However, like most drugs, ZzzQuil may cause some side effects. These side effects are largely caused by the drug’s blocking of the receptors for histamine and acetylcholine, and they can impact different parts of your body.

Talk with your doctor

ZzzQuil Nighttime Sleep-Aid may cause other possible side effects, so be sure to read the package before using the product. Remember, the active ingredient in this medication is not a commonly abused medication. As long as you use ZzzQuil as recommended for short periods of time, it’s not likely to lead to misuse or dependence. To make sure you use ZzzQuil safely, follow these tips:

  • Don’t take ZzzQuil every night.
  • Talk with your doctor if you have questions about how long you can take ZzzQuil and at what dosage. In general, taking this medication only from time to time should keep side effects to a minimum.
  • Talk to your doctor if you think this medication isn’t helping you sleep. Another medical condition could be causing your sleep problems.

Q:

Can you take too much ZzzQuil?

A:

If you don’t follow the package instructions, it’s possible to overdose on ZzzQuil. Taking too much can cause very serious side effects, such as dangerously low blood pressure or seizures. Be sure to follow the dosage instructions on the package carefully. If you have questions about how much ZzzQuil you should take, talk with your doctor of pharmacist.

Healthline Medical TeamAnswers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.