Metizolam

Metizolam is a synthetic thienodiazepine related to etizolam. It differs from etizolam by an additional methyl substituent on the thiophene-containing ring system. The compound was first identified in seized tablets in Europe in 2015 and later appeared on the online research-chemical market. Its pharmacological properties have not been characterised in controlled studies, although its metabolism has been examined in a small human observation and in vitro experiments.

Chemistry and identification

Metizolam belongs to the thienodiazepine group. Its structure is closely related to etizolam, but the additional methyl group changes the substitution pattern of the thiophene ring. The compound was identified in blue tablets seized in Germany and Denmark in 2015, with its identity confirmed by GC-MS and NMR analysis.

Pharmacology

No detailed receptor-binding or functional study has established metizolam’s pharmacological profile. Because of its structural similarity to etizolam, it is expected to act at the benzodiazepine site of the GABA_A receptor, producing sedative and anxiolytic effects. The exact potency and receptor selectivity remain uncertain.

A review of designer benzodiazepines found that user reports generally described metizolam as similar to etizolam, but with a less pronounced effect. These comparisons came from online reports rather than controlled head-to-head studies (New/Designer Benzodiazepines review, 2020).

Metabolism

A human observation and accompanying in-vitro study examined metizolam and its metabolites. Three mono-hydroxylated metabolites were produced in human liver microsomes. The main metabolite involved hydroxylation on the ethyl substituent, while another was identified as N-hydroxymetizolam. In urine, the main hydroxylated metabolite and its glucuronide were still detectable after the parent compound had declined (Kintz and colleagues, 2017).

Reported effects

The PsychonautWiki profile of metizolam draws on a few user reports of benzodiazepine-like effects. Sedation and reduced anxiety feature more prominently than euphoria.

Physical effects

Reported effects include drowsiness, muscle relaxation and reduced physical tension. Users describing stronger effects also report impaired coordination and sleepiness. These observations are consistent with the expected effects of GABA_A modulation, but have not been confirmed in clinical trials.

Cognitive effects

Online accounts mention anxiety reduction, lowered inhibition and memory impairment. Some describe a hypnotic effect, while others compare it with etizolam but report a less pronounced subjective response. The limited number of reports makes it difficult to establish a reliable effect profile.

Toxicity and dependence

There are no clinical studies that define the acute toxicity, long-term effects or dependence potential of metizolam. It was detected in a method-development study of urine samples from routine drug testing and emergency departments, showing that it has appeared in real-world exposure cases (Urine analysis of 28 designer benzodiazepines, 2018).

As with other benzodiazepines, repeated exposure may lead to tolerance and physical dependence. Combining it with alcohol, opioids or other sedatives can increase central nervous system depression. The extent of these risks has not been quantified specifically for metizolam.

Related compounds

Metizolam is closely related to Etizolam and Deschloroetizolam. It belongs to the same broad thienodiazepine group, but its additional methyl substituent gives it a distinct chemical structure.