You can now buy Narcan over the counter. Here's how to use it to reverse a fentanyl overdose.

• Fentanyl is a synthetic opioid that's 50 times stronger than heroin and 100 times more potent than morphine.
• Signs of overdose include loss of consciousness, weak breathing, and clammy or discolored skin.

On Wednesday, the FDA announced that it has approved the sale of naloxone nasal spray, also known as Narcan, for sale over-the-counter to treat opioid overdose. Previously, the medication had only been available by prescription. Now, the agency said, it will be sold at drug stores, grocery stores, gas stations, and online within the next several months.

Narcan is an opioid reversal medication, which works by binding to the opioid receptors to the brain, effectively "kicking off" the opioids from the receptors and replacing them for a limited amount of time. This can quickly reverse an overdose and restore breathing.

It works against all opioids, including fentanyl, a heroin-like drug that can be lethal in small doses. Fentanyl is one of the top substances driving overdose deaths in the US, according to the Centers for Disease Control and Prevention.

The illegal substance is highly addictive, and it may be added to other drugs to cheaply increase potency and keep consumers hooked. Since fentanyl lacks an odor or taste, some drug users don't know what they're dealing with until it's too late.

As a result, more than 150 people in the US die every day from overdoses related to fentanyl or similar synthetic opioids, according to the CDC.

Fentanyl can be made to look like cocaine, heroin, or prescription opioids in pill or powder form. It also comes as a liquid, as in nasal sprays or eye drops, which can be dropped onto paper like LSD.

Testing your drugs is the only foolproof way to be sure they are not laced with fentanyl, according to the CDC. Test strips are low-cost compared to other interventions, and they typically return results in five minutes or less.

Those minutes can make a life-saving difference in the case of a drug overdose, but not everyone is aware or has access to test strips. Here are some signs to look out for if things go wrong, and how to intervene:

How to spot an overdose

Pinpoint pupils

The symptoms of a fentanyl overdose are the same as any other opioid overdose, even though they may come on more quickly due to the drug's potency. In general, opioid overdoses occur about one to three hours after the drug is ingested, according to the New York State Department of Health.

All narcotic drugs — including fentanyl, heroin, and legal opioids like morphine — cause the pupils to constrict. Having "pinpoint pupils" is one symptom of overdose, especially if the pupils do not dilate in response to changes in light.

Pale, gray or bluish skin

Other signs of an overdose may include a pale or clammy face, and discoloration of the lips or fingernails, according to the CDC.

Bluish or purple discoloration is a sign to call 911 immediately, according to the Substance Abuse and Mental Health Services Administration. On people with darker colored skin, the skin may appear a grayish tint.

Vomiting

Vomiting, choking, or gurgling sounds may signal a potentially lethal overdose, according to SAMHSA.

If the person is awake, the CDC recommends calling 911 and staying with the individual until paramedics arrive.

If a person is unconscious and cannot vomit, or if they are having trouble breathing, lay the individual on their side to prevent choking.

Trouble breathing

Slow or weak breathing — or no breathing at all — is a cause for concern in any medical emergency, especially a fentanyl overdose.

Opioids are known to slow down all the body's systems, including the respiratory system. This may cause breathing to slow to a stop.

Unconsciousness

Normally, when a person is high on heroin or another opioid, they might go to sleep or slur their words, according to GoodRx. In contrast, someone who has overdosed may fall unconscious rather than asleep.

Call 911 if an individual who has taken drugs is unconscious and can't be woken up with a pinch to the ear or rub to the chest.

How to reverse an overdose using Narcan

First, call 911

Naloxone can temporarily restore normal breathing, but the effects only last 30 to 90 minutes. After that time, someone may require another dose, so it's best that emergency responders are on their way already.

Tilt the person's head back, and insert the spray nozzle

Naloxone comes in two forms — injectable and a nasal spray. The nasal spray version is the only one that will be available for people to get over the counter. When you are ready to administer the nasal spray, gently tilt the person's head back and provide support with your hand under their neck. Insert the tip of the nozzle into one nostril, until your fingers touch the bottom of the person's nose.

Press the plunger down the give the full dose

Once the nozzel is inserted, press the plunger down to give the full dose of the medication.

Watch for 2 minutes, then give a second dose if needed

Set a timer for two minutes, and wait to see if a person shows signs of overdose reversal, such as movement, increased breathing, or responding to questions. You can do rescue breaths during this time to help the person get oxygen into their lungs.

If the person does not respond, you can administer a second dose of Narcan — each package comes with two doses. Repeat this process until emergency services arrive.

As the person is recovering, you can roll them into the recovery position to prevent any risk of choking on vomit.

Stay with the person afterwards

After someone is revived after an overdose, they may be confused about what happened. Explain to them that they overdosed, and that you used Narcan on them. Because Narcan only lasts a short amount of time, stay with them until emergency services arrive. If emergency services isn't coming, stay with the person for at least 3 hours to make sure they won't need another dose after the Narcan wears off.