Clonazepam treatment of lysergic acid diethylamide-induced hallucinogen persisting perception disorder with anxiety features

Hallucinogen persisting perception disorder (HPPD) refers to the long-term recurrence of perceptual disturbances that resemble symptoms experienced during acute lysergic acid diethylamide (LSD) intoxication. The Introduction distinguishes between benign, transient “flashback” phenomena experienced by some users and HPPD, which is persistent, distressing and can cause substantial functional impairment. The authors summarise hypothesised mechanisms for HPPD, including LSD’s 5-HT2 partial agonist effects, enhanced glutamatergic transmission, damage or dysfunction of cortical serotonergic inhibitory interneurons (with GABAergic outputs) producing chronic disinhibition of visual processing, reverse tolerance or sensitisation after exposure, and possible familial or genetic predisposition. This study set out to evaluate clonazepam, a high-potency benzodiazepine with reported serotonergic properties, in the treatment of LSD-induced HPPD with co-occurring anxiety features. The investigation responds to clinical uncertainty about which benzodiazepines are most effective for HPPD and aims to assess symptomatic change during a fixed pharmacological trial and over a 6-month follow-up period.

Sixteen patients meeting DSM-IV diagnostic criteria for HPPD and reporting anxiety features were enrolled. Demographic details reported in the extracted text indicate 11 males and 5 females, mean age 21.125 years (SD = 2.500, range 17–24), unmarried, with about 12 years of schooling and middle-class social status. All participants had histories of polysubstance use (including cannabis, MDMA and LSD) but identified LSD as the trigger for their visual disturbances. The sample required a minimum of 3 months of HPPD symptoms and were confirmed drug-free for at least 3 months by random weekly urine drug screens. Prior trials with short-acting, low-potency benzodiazepines and other medications had been discontinued because of side‑effects or lack of benefit. Treatment began after informed consent. The extracted text describes an initial titration starting at 0.25 mg clonazepam twice daily on day one, with individual increases during the first week to avoid side-effects. The paper also reports the regimen as clonazepam 2 mg/day for 2 months and later refers to increases “up to 2 mg b.i.d.”; these statements are inconsistent in the extracted text and the exact target dose during maintenance is therefore unclear. After the 2-month treatment phase clonazepam was tapered by 0.5 mg weekly over 1 month to minimise rebound, and follow-up continued for 6 months after discontinuation. Clinical assessments were carried out weekly during the 8-week treatment period and then monthly during the 6-month follow-up. Outcome measures included the Clinical Global Impression Scale (CGI), a Self-Report Scale (SRS) that rates HPPD severity (1–5), and the Hamilton Anxiety Rating Scale (HAM‑A). The extracted text does not specify statistical procedures in detail; results are reported as comparisons from baseline to 8 weeks and from 8 weeks to the 6-month follow-up. Two patients dropped out during the 2‑month investigation and were removed from the analysed sample.

Two of the initial 16 participants discontinued treatment before the 2-month end point and were excluded from further analysis, leaving 14 completers according to the extracted text. Outcomes on the CGI, SRS and HAM‑A were compared from baseline to 8 weeks, and from 8 weeks to the 6‑month follow-up; a table with numerical results is referenced but not included in the extracted material. All three measures—CGI, SRS and HAM‑A—showed significant reductions after the 8‑week clonazepam procedure. A more granular analysis of the HAM‑A indicated significant improvement only on the items assessing anxious mood, tension, insomnia and intellectual (cognitive) symptoms; other HAM‑A items showed no change, described as a floor effect because of low baseline ratings. During the 6‑month post‑treatment follow-up there was additional improvement on the CGI and the SRS but not on the HAM‑A mean score. At the end of the pharmacological trial and throughout discontinuation and the clonazepam‑free follow‑up, only very mild symptomatology remained for most patients. The trailing phenomenon (objects producing discrete, discontinuous images as they move) was noted as particularly refractory. Adverse effects were generally mild: the most frequently reported were temporary daytime sedation and mild psychomotor impairment. The extracted text does not present precise effect sizes, confidence intervals or p‑values, nor does it provide the contents of the referenced table, so magnitude estimates beyond “significant reduction” cannot be stated from the provided material.

Lerner and colleagues interpret the findings as supporting a beneficial, sustained effect of clonazepam in patients with LSD‑induced HPPD accompanied by anxiety. They emphasise that HPPD is heterogeneous in presentation, that some cases remit spontaneously while others become chronic, and that the syndrome likely comprises several subtypes that may respond differently to medications. Given the predominance of open‑label and case‑report evidence in the literature, the authors note that pharmacological data are controversial and that double‑blind trials are difficult to conduct in this population. The discussion reviews alternative pharmacological approaches reported in earlier studies, including clonidine, dopamine antagonists, risperidone (which in some reports worsened symptoms), selective serotonin reuptake inhibitors (with mixed reports of benefit and worsening), reboxetine, combinations such as fluoxetine plus olanzapine, naltrexone, and anticonvulsants. Against this background, benzodiazepines are described as the treatment of choice for many patients, though not curative. The authors propose mechanistic rationales for clonazepam’s efficacy: benzodiazepine enhancement of GABAergic inhibition at cortical serotonergic interneurons, clonazepam’s reputed effects on serotonergic transmission potentially leading to 5‑HT2 receptor down‑regulation, and clonazepam’s high potency, long duration and relatively low abuse potential compared with some alternatives. Practical recommendations include careful prescribing and monitoring in patients with substance‑use histories, consideration of short courses or intermittent use for some patients, and the possibility of long‑term benzodiazepine therapy for those with treatment‑resistant, pervasive HPPD. Limitations acknowledged in the extracted text include the open‑label design, small sample size, methodological constraints and the absence of detailed dosing/duration answers; the authors call for further clinical investigations to clarify optimal dosing, duration and comparative efficacy.