[32] Balancing this medication and titrating the drug based on expected stimuli and the person's responses can result in stable blood pressure and heart rate throughout a procedure and a faster emergence from anesthesia with minimal pain.

[37] It is widely used in obstetrical anesthesia because of its short time to action peak (about 5 minutes), the rapid termination of its effect after a single dose, and the occurrence of relative cardiovascular stability.

When enough fentanyl has been absorbed, the (sedated) person generally lets the lollipop fall from the mouth, indicating sufficient analgesia and somewhat reducing the likelihood of overdose and associated risks.

[55][56] Some routes of administration such as nasal sprays and inhalers generally result in a faster onset of high blood levels, which can provide more immediate analgesia but also more severe side effects, especially in overdose.

[58] Fentanyl's most common side effects, which affect more than 10% of people, include nausea, vomiting, constipation, dry mouth, somnolence, confusion, and asthenia (weakness).

Less frequently, in 3–10% of people, fentanyl can cause abdominal pain, headache, fatigue, anorexia and weight loss, dizziness, nervousness, anxiety, depression, flu-like symptoms, dyspepsia (indigestion), shortness of breath, hypoventilation, apnoea, and urinary retention.

Existing studies advise medical practitioners to exercise caution when combining selective serotonin reuptake inhibitor (SSRI) drugs with fentanyl.

[69] The most dangerous adverse effect of fentanyl is respiratory depression,[70] that is, decreased sensitivity to carbon dioxide leading to reduced rate of breathing, which can cause anoxic brain injury or death.

[71] A prominent idiosyncratic adverse effect of fentanyl also includes a sudden onset of rigidity of the abdominal muscles and the diaphragm, which induces respiratory failure; this is seen with high doses and is known as wooden chest syndrome.

[77] Wooden chest syndrome is unique to the most powerful opioids—which today comprise fentanyl and its analogs—while other less-powerful opioids like heroin produce mild rigidity of the respiratory muscles to a much lesser degree.

[84] In July 2014, the Medicines and Healthcare products Regulatory Agency (MHRA) of the UK issued a warning about the potential for life-threatening harm from accidental exposure to transdermal fentanyl patches, particularly in children,[85] and advised that they should be folded, with the adhesive side in, before being discarded.

[106][107] A 2020 article from the Journal of Medical Toxicology stated that "the consensus of the scientific community remains that illness from unintentional exposures is extremely unlikely, because opioids are not efficiently absorbed through the skin and are unlikely to be carried in the air.

[111] A 2021 paper expressed concern that these physical fears over fentanyl may inhibit effective emergency response to overdoses by causing responding officers to spend additional time on unnecessary precautions and that the media coverage could also perpetuate a wider social stigma that people who use drugs are dangerous to be around.

The CDC recommended the following four actions to counter this rise:[117] Another initiative is a social media campaign from the United States Drug Enforcement Administration (DEA) called "One Pill Can Kill".

To prepare a sample for testing, approximately 10 mg of the drug, about the size of hair on Abraham Lincoln's head on a penny, should be diluted into 1 teaspoon, or 5 mL, of water.

[130] Research in Dr. Lieberman's lab at the University of Notre Dame has reported false positive results on BTNX fentanyl testing strips with methamphetamine, MDMA, and diphenhydramine.

[147] In the mid-1990s, Janssen Pharmaceutica developed and introduced into clinical trials the Duragesic patch, which is a formulation of an inert alcohol gel infused with select fentanyl doses, which are worn to provide constant administration of the opioid over 48 to 72 hours.

[150] It uses a medication delivery technology called BEMA (BioErodible MucoAdhesive), a small dissolvable polymer film containing various fentanyl doses applied to the inner lining of the cheek.

While U.S. officials blame the flood of fentanyl crossing the border primarily on Mexican crime groups, then-President Andrés Manuel López Obrador insisted that the main source of this synthetic drug is Asia.

[167] The attorneys general of Connecticut and Pennsylvania have launched investigations into its diversion from the legitimate pharmaceutical market, including Cephalon's "sales and promotional practices for Provigil, Actiq and Gabitril.

In 2006, illegally manufactured, non-pharmaceutical fentanyl often mixed with cocaine or heroin caused an outbreak of overdose deaths in the United States and Canada, heavily concentrated in the cities of Dayton, Ohio; Chicago, Illinois; Detroit, Michigan; and Philadelphia, Pennsylvania.

[174] One US Department of Justice publication lists "China White" as a synonym for a number of fentanyl analogues, including 3-methylfentanyl and α-methylfentanyl,[175] which today are classified as Schedule I drugs in the United States.

[176] In June 2013, the United States Centers for Disease Control and Prevention (CDC) issued a health advisory[177] to emergency departments alerting to 14 overdose deaths among intravenous drug users in Rhode Island associated with acetylfentanyl, a synthetic opioid analog of fentanyl that has never been licensed for medical use.

Authorities suspected that the drug was being imported from Asia to the western coast by organized crime groups in powder form and being pressed into pseudo-OxyContin tablets.

[182] In 2018, Global News reported allegations that diplomatic tensions between Canada and China hindered cooperation to seize imports, with Beijing being accused of inaction.

[197][198][199] Recent investigations and convictions of members of the Sinaloa drug cartel by federal agencies made a clear connection between illegal arms trafficking from the U.S. to Mexico and the smuggling of fentanyl into the U.S. Mexico had repeatedly made official complaints since illegal guns are easily purchased for example in Arizona and as far north as Wisconsin and even Alaska, according to U.S. intelligence sources, and transported onto Mexican territory through a chain of American brokers and couriers often financed by those drug cartels that also engage in money laundering.

In British Columbia, Canada, where there are environmental concerns about toilet flushing or garbage disposal, pharmacists recommend that unused patches be sealed in a child-proof container that is then returned to a pharmacy.

Moore received a lethal injection, administered as an intravenous series of four drugs that included fentanyl citrate, to inhibit breathing and render the subject unconscious.

[256] In April 2023, Teva Pharmaceuticals USA recalled 13 lots of their Fentanyl Buccal Tablets CII due to missing safety information sheets on how to properly administer their product.

In addition, its efficacy is higher than many other pure-opiate and synthetic pure-opioid agonists regarding vomiting, depth of sedation, and cardiovascular effects when given as a continuous infusion as well as a transdermal patch.