Summarised in our own words, each with a retrievable citation. Single case reports unless stated otherwise.
Tolerance can develop within weeks, and dependence with it[9]
A man in his twenties presented to an emergency department asking for help with detoxification. He had begun using phenibut bought online roughly a month earlier while also drinking heavily, and had found that the amount that once worked stopped working — the report notes that tolerance to phenibut has been described as developing within one to two weeks. When he tried to stop on his own he developed cold sweats, anxiety, insomnia, and both visual and auditory hallucinations. His clinicians described a withdrawal that resembled alcohol withdrawal but ran longer and more severely than his drinking alone would explain, and concluded that phenibut dependence was adding to it. He was managed with benzodiazepines for the acute withdrawal alongside psychiatric medication for anxiety and protracted symptoms.
A single published case report. It describes what happened to one patient; it does not establish how often this happens.
Withdrawal can present as an agitated delirium that standard treatment does not touch[7]
A woman in her fifties was brought to an emergency department with severe psychomotor agitation, disorganised thinking, visual hallucinations, and a complete inability to sleep. Her partner reported that the movement disturbance and fluctuating alertness had come on suddenly that morning. Her urine toxicology screen showed only benzodiazepines, which she used legitimately, and her presentation was initially read as a primary psychiatric episode. Benzodiazepines and antipsychotics did not work. The cause only became clear when her partner found phenibut at home and a poison centre was called; her symptoms had begun about three days after she stopped taking it, following months of regular use. She was treated with baclofen as a substitute at the same receptor, along with escalating benzodiazepines, antipsychotics chosen with cardiac monitoring in mind, and beta-blockers for blood-pressure and heart-rate instability. She was in hospital for roughly three and a half weeks, and her psychotic symptoms resolved by the fourth week.
A single published case report. Its value here is diagnostic: it documents a presentation that was missed precisely because the drug does not appear on a standard screen.
Withdrawal can outlast the hospital stay, and benzodiazepines can make it worse[8]
A man in his thirties was admitted after a suicide attempt. He had been buying phenibut from internet vendors and escalating his use over a period of weeks, and described a dream-like, out-of-body state along with several days without sleep. On arrival he was tachycardic with dilated pupils and flushed skin, and although he remained oriented, his thinking was tangential and illogical. Withdrawal began on his second hospital day and brought agitation, disorientation, visual hallucinations, and tremor that lasted about a week. Notably, treatment with diazepam appeared to worsen rather than settle his condition; he was subsequently managed with baclofen and was clear-thinking and fully oriented by the ninth day.
A single published case report. The paradoxical response to a benzodiazepine is one observation in one patient, not an established pharmacological rule.
Acute presentations can require airway protection and intensive care[10]
A man in his thirties with a history of polysubstance use was brought in by ambulance after being found at home behaving incoherently. He arrived agitated, confused, and resistant to care, with a Glasgow Coma Scale score in the mildly impaired range. Repeated intravenous lorazepam over a quarter of an hour had minimal effect, and he was intubated and mechanically ventilated because he could not cooperate with care safely. His urine screen was positive for benzodiazepines and cannabinoids; ethanol, salicylate, acetaminophen, and ammonia were all below detection, and his bloodwork showed a raised white cell count, lactic acidosis, and an elevated anion gap. He was admitted to intensive care, extubated two days later, and discharged home after psychiatric consultation.
A single published case report. Broader poison-centre and review literature describes central nervous system depression, coma, and respiratory depression requiring intubation in phenibut cases, particularly alongside other depressants.