In the rapidly evolving ‘legal highs’ market, synthetic cannabinoids play a predominant role. These potent synthetic cannabinoid receptor agonists produce effects similiar to those of delta-9-tetrahydrocannabinol and are usually added to herbal smoking mixtures by soaking or spraying. Typical marketed as so-called herbal incense (potpourri), they are widely and openly sold on the web with the synthetic cannabinoids used in the mixtures continuously being substituted by ‘legal’ alternatives, in pace with new control measures. A seizure of ‘spice-like’ herbal incense was submitted to the laboratory for toxicological analysis. A methanolic sample solution was analyzed using liquid chromatography with diode array detector and gas chromatography-mass spectrometry. The μ-opioid receptor agonist U-47700 was found to be the only psychoactive substance present in the herbal mixture. Although considerable inter-batch differences in the concentration can be expected, a quantitative determination was performed in order to obtain an indication regarding the potency of the seized herbal mixture. In light of the emerging threat of synthetic opioids fatalities, the presence of U-47700 in ‘spice-like’ herbal incense raises great concerns, since the abuse may pose serious risk, as users will likely not be aware that they are using a potent synthetic opioid. This case illustrates once again that new psychoactive active substances openly sold on the Internet as ‘legal highs’ pose a risk for public health.