Central nervous system — or CNS — depression happens when the body's normal neurological functions slow down. It can result from substance overdoses, poisoning, or other medical conditions.

Depression of the central nervous system or CNS often occurs when a person misuses a substance that slows brain activity. These substances are called CNS depressants.

Examples of CNS depressants include tranquilizers, hypnotics, and sedatives. In recent years, doctors have prescribed opioid painkillers for many conditions, but overuse of these drugs can lead to problems.

People also use them as recreational drugs. Recreational use can be illegal and dangerous, as people may not understand the risks of misuse.

Combining different CNS depressants, such as painkillers and alcohol, can be life-threatening.

Find out here more about the uses and risks of CNS depressants.

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People should use sleeping pills, pain-relief medication, and other CNS depressants with caution.

A person may benefit from taking the correct dose of a CNS depressant, such as an opioid pain relief medication.

But, high doses of these drugs can reduce the activity of the CNS to dangerously low levels.

The CNS consists of the brain and spinal cord. It controls most bodily functions — including breathing and the heart — by sending messages between the brain and other nerves via the spinal cord.

It plays a role in essential bodily processes:

Involuntary processes: These do not need conscious thought. They regulate vital organs such as the heart, lungs, and stomach. They are responsible for functions, including digestion and blood circulation.

Voluntary processes: These involve conscious thought. They enable people to move their arms and legs, for example, or to blink their eyes.

CNS depressants are medications and other substances that slow down the CNS.

Many CNS depressants work by increasing the activity of the neurotransmitter gamma-aminobutyric acid (GABA), a chemical that prevents or slows the delivery of messages between cells.

People can have varying symptoms of CNS depression or depressant overdose. Factors that affect the impact of CNS depression include:

  • the cause
  • the type and dose of a substance
  • the severity of the illness or injury
  • the size of the individual
  • the person's medical history

Mild symptoms

Mild symptoms of CNS depression include:

lack of coordination and impaired sense of space

  • muscle weakness
  • lethargy
  • dizziness
  • disorientation
  • slurred speech or stuttering
  • slight shortness of breath or shallow breathing
  • slightly reduced heart rate
  • constipation
  • dry mouth
  • restlessness and agitation
  • euphoria
  • blurred, altered, or double vision

Severe symptoms

Symptoms of severe CNS depression include:

  • reduced heart rate
  • low breathing rate of fewer than 10 breaths per minute
  • extreme confusion or memory loss
  • nausea and vomiting
  • poor judgment
  • blue lips or fingertips
  • irritability and aggression
  • clammy or cold skin
  • sudden and intense mood swings
  • slow reflexes

If a person has any of these symptoms, they should seek immediate medical care. Ultimately, severe symptoms can lead to unresponsiveness, coma, and death.

Long-term effects

Continued use of some CNS depressants can be harmful long-term, as the body becomes unable to flush out these substances.

Effects may include:

  • problems with thought, memory, and judgment
  • disorientation and confusion
  • muscle weakness
  • loss of coordination
  • slurred speech

Also, the individual may need more and more of the drug to experience the same benefits. This greater need can lead to dependence. Some people may need rehabilitation therapy to stop using the drugs.

Several substances can depress the CNS, ranging from anti-anxiety and sleep medications to so-called recreational drugs, such as heroin.

Medications, drugs, and other substances

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Opioids can be useful in relieving pain, but they can be very dangerous, too.

The main substances that cause CNS depression are:

  • alcohol
  • barbiturates
  • benzodiazepines
  • opioids

Most of these drugs cause some combination of drowsiness, muscle relaxation, and anxiety reduction.

The National Institute on Drug Abuse (NIDA) note that CNS depressants may be safe when used correctly, but they always have a risk of addiction.

Many medically prescribed and high-dose depressants are also common street drugs, and some people use them recreationally.

Non-drug causes

CNS depression does not only result from the use of medications and other substances.

Non-drug causes include:

Other medical conditions that increase the risk of CNS depression include:

  • kidney, lung, heart and liver disease
  • diabetes
  • thyroid disorders

People with any of these conditions should check with a doctor before using a CNS depressant.

Doctors commonly prescribe some types of CNS depressant for various reasons.

Opiates and opioids

These are strong pain-relieving drugs that come from opium, a substance made from the seeds of the poppy.

Opiates are the active ingredients in opium, heroin, morphine, and codeine. Opioids are derived from opiates, such as oxycodone, hydrocodone, and heroin.

Both opiates and opioids work by interfering with the CNS and blocking pain signals to the brain.

Commonly prescribed opiates and opioids are:

  • oxycodone (OxyContin)
  • hydrocodone (Vicodin)
  • morphine (Kadian, Avinza)
  • codeine
  • fentanyl (Duragesic)
  • methadone
  • hydromorphone (Dilaudid)

Doctors may prescribe these drugs for pain relief. Given their strength and addictive qualities, only people who have a severe condition should use them.

Some of these substances, for example, codeine, are present in medications for coughs or diarrhea. Doctors will prescribe these for short-term use only.

Some people also use opioids and opiates, such as heroin, as recreational drugs. Common street names include H, smack, oxy, and China white.

Sleep medications

These are chemically different from other CNS depressants, but they work by stimulating the same inhibitory neurotransmitter, GABA.

Common sleep medications that doctors may prescribe are:

  • zolpidem (Ambien)
  • zaleplon, (Sonata)
  • eszopiclone (Lunesta)

Street names for sleep medications include zombie pills, sleepeasy, and tictacs.

Benzodiazepines

These are a treatment option for conditions that can include stress reactions, panic attacks, sleep disorders, and convulsions.

Examples of benzodiazepines include:

  • alprazolam (Xanax)
  • clonazepam (Klonopin)
  • diazepam (Valium)
  • lorazepam (Ativan)
  • estazolam (ProSom)

Benzodiazepines can also be a drug of abuse. Street names include benzos, downers, and chill pills.

Barbiturates

These can treat seizure disorders and anxiety, but doctors rarely prescribe them nowadays. Before surgery, they may promote sleep and relaxation.

Examples include:

  • mephobarbital (Mebaral)
  • sodium phenobarbital (Nembutal)

As a recreational drug, people sometimes call them barbs, downers, or phennies, among other names.

Crime-related drug use

Sexual and violent crime are other areas where people are known to misuse CNS depressants. The sedative Xyrem, known as the "date rape drug," commonly features in cases of sexual assault.

Xyrem is easily hidden in drinks, as it is odorless, colorless, and tasteless when mixed with liquid.

When people use CNS depressants, it can be hazardous for many reasons, including:

  • dependency
  • withdrawal symptoms when ending their use
  • overdose
  • long-term adverse effects

Misuse can also happen if a person uses someone else's medication, if they take more than the recommended dose, or if they use drugs that a doctor has not prescribed.

Combining substances

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Combining CNS depressants, for example, alcohol with sleeping pills, can be dangerous.

Mixing CNS depressants, opioids, and alcohol increases their effect. There may be severe adverse reactions and possibly life-threatening consequences.

Sometimes, a person may not realize they are at risk of an overdose, such as when they use opioid pain relief medication and then drink alcohol.

Prescription benzodiazepines and opioids carry the highest level of warning from the U.S. Food and Drug Administration (FDA), because of their risks.

People should check first with their doctor to find out if it is safe to take CNS depressant medication and any of the following:

  • alcohol
  • over-the-counter medicines with similar properties, such as painkillers
  • allergy medications
  • sleeping aids

Tricyclic and tetracyclic (TCA) antidepressants can also intensify the effects of CNS depressants, especially drowsiness.

Dependence and withdrawal

Some CNS depressants become less effective over time, so that a person may feel the need to take a larger dose. If they stop using the drug, the original symptoms can return more severely than before.

A person who wishes to stop using a CNS depressant may need to stop gradually to prevent adverse effects. A doctor can help them to do this.

Overdose

An overdose of a CNS depressant can happen by accident, but people sometimes choose to take more of the drug than a doctor recommends to get a more "intense" effect. This can lead to overdose and death. People have also been known to overdose on these medications deliberately to end their lives.

A person may recover from an overdose, but research in the Journal of Clinical Psychopharmacology shows that some may continue to have problems with everyday functioning after leaving the hospital.

Long-term effects

Some types of CNS depressant can also have long-term effects, causing someone to have difficulty thinking, confusion, speech problems, loss of coordination, and muscle weakness.

Addiction to CNS depressants may see a person experience social and family problems, difficulty working, and an inability to function in daily.

The opioid crisis: Some figures

Since 2000, more than 300,000 Americans have died of an opioid overdose. Data for 2016 estimates at least 64,000 drug overdose deaths, the highest number ever recorded in the United States.

Overdoses of prescription painkillers in the U.S. is a growing problem, especially among women, according to the Centers for Disease Control and Prevention (CDC).

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Severe symptoms of CNS depression include loss of consciousness, coma, and death. Anyone with these symptoms needs immediate medical help.

Treatment for CNS depression or CNS depressant overdose depends on the substances involved.

Some CNS drugs have antidotes that can reverse their effects. These include Naloxone for opioid overdoses and Flumazenil for overdoses of benzodiazepine.

A person may need emergency care if they are unaware that they are experiencing a CNS depressant overdose, especially after accidentally misusing their medication or due to a medical problem.

Anyone witnessing signs of CNS depression or an overdose in another person should call the emergency services or local poison control center for guidance.

In these cases, treatment may include:

  • monitoring the person's breathing and heart rate.
  • giving oxygen via an oxygen mask or respirator
  • administering stimulant drugs to increase a person's heart rate

In the U.S., anyone who is concerned that they or someone they know is misusing CNS depressants can:

  • call 1-800-662-HELP (4357) or 1-800-487-4889 to find their nearest Substance Abuse Treatment Facility for help and advice
  • access the Substance Abuse and Mental Health Services Administration (SAMHSA) website for help and advice

These services offer free and confidential advice, 24/7, in English or Spanish.

The National Suicide Prevention Lifeline can help with a wide range of problems. People can contact them for a confidential chat on 1-800-273-8255 or 1-800-273-TALK.

CNS depression or overdose is a common cause of poisoning in many developed countries, including the U.S. and Canada.

People who take CNS depressants must be aware of the risks and should never share drugs or take a substance without knowing what is in it.

Only a doctor should prescribe a CNS depressant, and people should only use these drugs for the specified purpose, according to the doctor's instructions.

Q:

My doctor has prescribed Oxycodone for my chronic back pain. Is it dangerous for me to use this medication? Nothing else seems to work.

A:

There is no way to know who may become addicted to an opiate medication.

The most important thing is to be honest with your prescriber regarding your symptoms, and to communicate honestly. Discuss treatment goals and alternatives to the use of opiates so that opiate use is limited.

For some people, limiting the duration of use of opiate medications may not be possible, and in these cases, ongoing communication and honesty with your prescriber is essential for adequate monitoring of both pain and side effects.

Timothy J. Legg, PhD, CRNP Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.