Phenibut: an Eastern European medicine sold online as a supplement

A test for phenibut checks whether the drug is present in a sample, and Diagnostiek voor U expresses the amount found in micrograms per millilitre (µg/mL). Diagnostiek voor U has the determination done at MVZ Dessau, and Unilabs sends its screen for new psychoactive substances to the Apotheek Haagse Ziekenhuizen, where LC-HR-MS is used, a form of mass spectrometry that recognises a substance by its exact mass.

Phenibut is promoted online with claims such as "helps balance mood" and "promotes focus, relaxation, and positive mood", which the authors of a 2024 review came across in their search for phenibut products and call deceptive. According to the same review, phenibut has a strong potential to interact with other drugs, such as anti-anxiety drugs, antipsychotics, sedatives, opioids and anti-epileptic drugs.

Phenibut is banned in France, Italy and Lithuania, in the United States and in Australia according to the review, and yet it is easy to obtain online.

According to the Apotheek Haagse Ziekenhuizen (AHZ), which runs the Unilabs urine screen for new psychoactive substances, that screen, which also covers phenibut, is meant for suspected misuse or poisoning and for monitoring during withdrawal. According to a 2024 review, phenibut is missing from standard drug screening protocols, which often stands in the way of a proper diagnosis. For its urine screen for new psychoactive substances Unilabs counts on a turnaround of 2 weeks, and Diagnostiek voor U gives 13 days for phenibut, from arrival at the lab to the result, for 95% of determinations.

A detection period in days for phenibut cannot be found in the sources read; the review gives only a half-life in the blood of 5.3 hours, measured in one study after a single 250 mg dose in healthy volunteers.