U-47700 also recognized as U4, pink heroin, pinky, or pink, is an opioid analgesic drug initially developed by a team at Upjohn during the 1970s. In animal models, it boasts approximately 7.5 times the potency of morphine.
A physical sample of U-47700 is available for reference.
This compound is a structural isomer of the earlier opioid AH-7921 and is the culmination of extensive research into the quantitative structure-activity relationship of its chemical framework. Upjohn systematically explored the crucial structural components that contributed to its potent activity and secured more than a dozen related patents, each aimed at enhancing specific structural elements. Eventually, they identified U-47700 as the most active variant among them.
U-47700 has served as the foundational compound for the development of selective kappa-opioid receptor ligands, such as U-50488, U-51754 (featuring a pyrrolidine substituent instead of dimethylamine), and U-69,593, which share remarkably similar structural characteristics. While these selective kappa ligands are not employed for medical purposes, they play a significant role in scientific research.

IUPAC name
CAS Number82657-23-6
PubChem CID13544016
CompTox Dashboard (EPA)DTXSID001014181
Chemical and physical data
Molar mass329.27 g·mol−1


U-47700 acts as an agonist for the μ-opioid receptor (Ki 11.1 ± 0.4nM), displaying notably reduced affinity for the κ-opioid receptor (Ki 287 ± 24nM) and δ-opioid receptor (Ki 1220 ± 82nM). In rats, U-47700 exhibits approximately 10-fold greater potency than morphine, although its binding affinity at all three opioid receptors is 2-4 times weaker compared to morphine.
The human metabolism of U-47700 entails mono- anddidesmethylation followed by hydroxylation. Importantly, the desmethyl metabolites of U-47700 exhibit minimal affinity for opioid receptors and are not believed to contribute significantly to U-47700’s pharmacological activity.

Side effects

While U-47700 has not been subjected to human studies, it is anticipated to elicit effects akin to those observed with potent opioid agonists. These effects encompass robust pain relief, sedation, feelings of euphoria, constipation, itching, and the potential for harmful or fatal respiratory depression. Additionally, the use of U-47700 has been linked to instances of tachycardia. The development of tolerance and dependence is also expected.
Incidents of Deaths:
Tragically, fatalities have been associated with U-47700 use. In Belgium and Germany, one fatality each resulted from the combined consumption of U-47700 with fentanyl and flubromazepam, respectively.[34][35][36] Ireland reported one death, while another occurred in Italy.[37][38] In the United States, U-47700 was initially linked to 17 opioid overdoses and several deaths in April 2016, with at least 15 confirmed fatalities as of September 2016. By December 2017, the number of fatalities associated with U-47700 had surged to at least 46 cases. Notably, U-47700 was detected alongside fentanyl during the autopsy of the renowned American artist Prince in 2016.
Detection in Biological Fluids:
U-47700 may be quantified in serum, plasma, blood, or urine to monitor its abuse potential, validate poisoning diagnoses, or aid in medicolegal death investigations. In individuals who have consumed the substance, serum or blood U-47700 concentrations typically fall within the range of 10–250 μg/L, while in cases of acute overdose leading to death, these concentrations can range from 100–1,500 μg/L. The detection process generally involves analysis employing liquid chromatography-mass spectrometry.

Legal status

After being sold as a designer drug, Sweden declared U-47700 illegal on January 26, 2016.
In Ohio, Governor John Kasich issued an executive order on May 3, 2016, to emergency schedule U-47700.
Florida Attorney General Pam Bondi issued an emergency rule on September 27, 2016, to emergency schedule U-47700 in Florida due to concerns about public health and safety.
In response to perceived threats to public health and safety, the U.S. Drug Enforcement Administration (DEA) classified U-47700 as a Schedule I controlled substance, effective from November 14, 2016. Subsequently, in April 2018, U-47700 was permanently placed in Schedule I.
South Dakota included U-47700 in Schedule I of its Controlled Substance Schedule, with Governor Daugaard signing it into law on February 9, 2017.


1. What is U-47700?

U-47700, also known by various street names like U4, pink heroin, pinky, and pink, is a synthetic opioid analgesic. It was initially developed in the 1970s by Upjohn, a pharmaceutical company.

2. What are the effects of U-47700?

U-47700 produces effects similar to other potent opioids, including pain relief, sedation, euphoria, constipation, itching, and, most critically, respiratory depression, which can be life-threatening.

3. Is U-47700 legal?

U-47700 is classified as a controlled substance in several countries and regions. Laws regarding its legality can vary, but in many places, it is illegal to manufacture, possess, or distribute U-47700.

4. Is U-47700 safe to use?

No, U-47700 is not safe for use. It is associated with a high risk of respiratory depression, overdose, and death, even at relatively low doses. Using U-47700 is extremely dangerous and not recommended.

5. What is the history of U-47700’s legal status?

The legal status of U-47700 has changed over the years. It was initially sold as a designer drug but has since been classified as a controlled substance in many places. Laws regarding its status can change, so it’s essential to check local regulations for the most up-to-date information.

6. Is U-47700 addictive?

Yes, like other opioids, U-47700 has a high potential for tolerance, dependence, and addiction. Using it regularly can lead to physical and psychological dependence.

7. Are there any reported deaths associated with U-47700 use?

Yes, there have been numerous reported deaths associated with U-47700 use. It has been linked to overdoses and fatalities, often when used in combination with other substances.

8. How can U-47700 be detected in the body?

U-47700 can be detected in biological fluids like blood, serum, plasma, or urine using specialized testing methods, such as liquid chromatography-mass spectrometry. Concentrations can vary depending on the individual’s use and circumstances.

9. Is there any legitimate medical use for U-47700?

U-47700 is not approved for medical use and is not prescribed by healthcare professionals. It is considered a dangerous substance with no recognized therapeutic benefits.

10. What should I do if I suspect someone has used U-47700?

If you suspect someone has used U-47700 and is experiencing symptoms of overdose, such as difficulty breathing, extreme drowsiness, or loss of consciousness, seek immediate medical attention. Do not attempt to treat an overdose on your own.

11. Where can I get more information about U-47700?

For more information about U-47700, its legal status in your area, and its risks, consult your local health department, law enforcement agencies, or substance abuse treatment centers. Additionally, medical professionals and addiction counselors can provide valuable guidance and resources.


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