Objectives:
The study was aimed to analyze information posted by users of synthetic opioids on Polish online drug discussion forums. Special emphasis was given to sources of drugs and their availability, routes of administration, dosages, expected and toxic effects.

Methods:
6,143 reports related to synthetic opioids, posted between 2005 and mid 2019 on three widely available popular Polish online forums devoted to psychoactive substances, i.e., https://hyperreal.info/talk, https://dopek.info and https://forum.dopalamy, were collected and analyzed.

Results:
Fentanyl was the most widely used and relatively easily accessible synthetic opioid in Poland. Butyrfentanyl and furanylfentanyl, were far less popular. The main source of fentanyl was diversion of medicines, notably transdermal patches. Synthetic opioids are administered orally, buccally, sublingually, intranasally, by inhalation and intravenously. Concomitant use of fentanyl and its derivatives with other psychoactive compounds increases the risk of severe adverse effects.

Conclusions:
Our study contributed to a more comprehensive understanding of problems related to abuse of fentanyl, butyrfentanyl and furanylfentanyl in Poland. In the light of the relatively high popularity of pharmaceutical fentanyl used for non-medical purposes, there is an urgent need for more strict control over illegal sales of fentanyl transdermal preparations, as well as disposal of used patches. Furthermore, patients using fentanyl should be warned that giving it to another person is against the law, and may lead to serious health consequences. It is important to educate the society in order to increase awareness of the problem of opioid use, and to pay attention to signals which may indicate addiction among family members.