About Fentanyl

Fentanyl is a human made opioid. It is 50-100 times stronger than morphine. Fentanyl is causing high rates of overdose deaths in San Francisco and in cities across the nation.

An image of fentanyl and heroin side by side.

What is Fentanyl?

  • Fentanyl is a human made opioid. It is 50-100 times stronger than morphine. 
  • Some fentanyl is legal and prescribed by doctors for severe pain. It is dangerous if not used as prescribed. 
  • Some fentanyl is not legal. Illegal fentanyl is causing high rates of overdose deaths. This is happening in San Francisco and the rest of the United States.   
  • Fentanyl is cheap. It is often mixed into other drugs. Heroin, cocaine, methamphetamine and MDMA may contain fentanyl. People may not know that fentanyl is in their drugs, which can lead to overdose.   

How can someone tell if fentanyl is present in their drugs?

It is not possible to know whether fentanyl is present in drugs by smell or taste. It is hard to tell exactly how much fentanyl is present. Because fentanyl is so strong, even very small amounts of fentanyl can cause an overdose.   

Fentanyl test strips can help tell you if fentanyl is in a drug sample. They work in 1-2 minutes. Although they cannot tell you how much fentanyl is present.   
To get up to 10 fentanyl test strips, visit:  

Behavioral Health Services Pharmacy  
1380 Howard St., 1st floor 
San Francisco, CA 94103  

What are the effects of fentanyl?

Fentanyl is an opioid. Some prescription pain medications and heroin are also opioids. Opioids relieve pain. They also cause a "high." Opioids also cause sleepiness and slowed breathing. They can also lead to addiction. 

Someone who uses fentanyl can become dependent. This means they will have withdrawal symptoms if they stop using it. These symptoms are treatable. 

Withdrawal symptoms include: 

  • body aches 
  • shivers 
  • anxiety 
  • vomiting and diarrhea 

Fentanyl can also cause addiction. Addiction is when a person has a craving and continues to use a substance despite it causing them harm. Fentanyl addiction is treatable.  

A person who uses fentanyl often can also become tolerant. Tolerance means a person will need to take more of the drug to feel the same effect. After some time, a person may no longer even feel the high from the drug. 

How does fentanyl cause an overdose?

Like other opioids, fentanyl slows a person’s breathing. At its most extreme, fentanyl stops a person’s breathing. If breathing is not restored, the lack of oxygen can cause death. 

This is how fentanyl is causing so many overdose deaths in San Francisco and many other cities.

Can someone overdose on fentanyl by touching it?

No, it is not possible to overdose on fentanyl by touching it.  

What are risk factors for a fentanyl overdose?

The risk of fentanyl overdose depends on the strength of the drug. It also depends on how much someone takes. People who drink alcohol while using other drugs at the same time are at higher risk of overdose. It also matters how tolerant a person is to opioids. 

Strength of the drug 

Small amounts of fentanyl can cause overdose because it is so strong. 

People who use drugs alone can overdose because there is no one nearby to ask for help. Taking more than one drug at a time can also cause overdose. Overdose is more likely when mixing fentanyl with alcohol or benzodiazepines, like Xanax or Ativan. 


When a person uses less or no fentanyl, their tolerance goes down. This can happen in as little as a few days. If that person starts using fentanyl again, they are at high risk of an overdose. The same amount of fentanyl is more likely to lead to an overdose because their body is less used to the drug.

What are the signs of fentanyl overdose?

Signs of a fentanyl overdose include: 

  • Decreased alertness or being unresponsive 
  • Cold and clammy skin 
  • Blue skin or lips 
  • Small pupils 
  • Slow or no breathing 

Learn how to recognize and reverse an overdose via this SFDPH developed training series. 

Can naloxone (also known as Narcan) be used to reverse a fentanyl overdose?

Yes. When given correctly and quickly, naloxone can reverse an overdose. No opioids are "naloxone-resistant." Naloxone saves lives. 

Naloxone may not work if it is given too late. It might also not work if a non-opioid drug led to the overdose. Some stronger opioids, like fentanyl, may need more than one dose of naloxone to reverse. 

You should always give naloxone when worried about an overdose. If you don't know what drugs someone has used, it is OK to give naloxone. You cannot hurt someone with naloxone if fentanyl or other opioids are not present. 

To get a free nasal naloxone kit and training, visit:  

Behavioral Health Services Pharmacy  
1380 Howard St.,1st floor 
San Francisco, CA 94103  

What happens when someone who regularly uses fentanyl stops using it?

People who use fentanyl daily experience withdrawal when they stop using it. Withdrawal symptoms include: 

  • Body aches 
  • Shivers and sweats 
  • Anxiety 
  • Diarrhea and vomiting 
  • Cravings for opioids 

These symptoms can be severe. They can start within hours of stopping fentanyl and last for days.

Can fentanyl addiction be treated?

Addiction to fentanyl is treatable. Medications like methadone and buprenorphine are effective. They work by reducing cravings. These medicines lower the risk of dying by 50%. 

  • Methadone is a daily oral medicine. It is available at special treatment programs. 
  • Buprenorphine is a daily oral medicine or a monthly injection. Primary care doctors can prescribe it.   

Methadone and buprenorphine reduce the risk of dying by up to 50%.  

Behavioral therapies also help treat addiction. 

  • Cognitive behavioral therapy: Helps people change by learning to manage stress and triggers.  
  • Contingency management: works by rewarding people who reduce their drug use. It is the most effective treatment for people who use cocaine and methamphetamine." 
  • Behavioral therapies also help treat addiction. They work best when used with medications. Learn what treatments are available here.

How can I help?

  • Learn how to tell when someone is overdosing.  
  • Learn how to give naloxone for an overdose  
  • Carry naloxone with you. 
  • Call for medical help when you are worried about someone using drugs. 
  • Sign up for this training.  
Last updated March 5, 2024