HHC Crossed Into Rat Brains, Caused Anxiety, and Was Classified as Low-Toxicity | Research

The takeaway

Hexahydrocannabinol crossed the blood-brain barrier in rats, caused dose-dependent anxiety and impaired sensory processing, and was classified as a Category 4 toxicity substance.

toxicologists, drug policy researchers, consumers of HHC products, regulators

What the researchers found

A 1:1 mixture of (9R)-HHC and (9S)-HHC reached peak blood and brain concentrations 2 hours after the highest dose (10 mg/kg). OECD 423 toxicity testing classified HHC as Category 4 (estimated lethal dose 1000 mg/kg). At 10 mg/kg, HHC reduced movement, increased anxiety-like behavior, and impaired prepulse inhibition of acoustic startle response.

Why it matters

HHC is widely sold as a legal THC alternative in parts of Europe and the UK, but safety data have been almost nonexistent. This is among the first studies characterizing its pharmacokinetics, toxicity, and behavioral effects.

The numbers in context

Doses: 1, 5, 10 mg/kg. Peak brain concentration at 2 hours post-10 mg/kg dose. OECD Category 4 toxicity (estimated LD50: 1000 mg/kg). 10 mg/kg reduced locomotion, increased anxiety, impaired sensory gating. Vehicle: sunflower oil.

How the study worked

Male Wistar rats received a 1:1 mixture of (9R)-HHC and (9S)-HHC via intragastric gavage at 1, 5, and 10 mg/kg. Behavioral effects assessed via open field test and prepulse inhibition. Pharmacokinetics measured in blood and brain tissue. Toxicity classified per OECD 423 protocol.

What this study cannot tell us

Male rats only. Used a racemic mixture rather than individual stereoisomers. Oral gavage dosing may not reflect typical human consumption routes (vaping, edibles). Acute effects only, no chronic exposure data. Limited behavioral battery.

How to read the evidence

Systematic toxicology and behavioral assessment in an animal model, but single species, male-only, and acute dosing limit the evidence to preliminary.

When this study was published

Recently published, among the first HHC toxicology studies.

The bigger picture

As novel cannabinoids like HHC proliferate in legal gray areas, basic safety data are urgently needed. This study provides an initial toxicological profile, but the anxiety-inducing and sensory-impairing effects at higher doses raise concerns about the unregulated market.

Questions still open

Do the two HHC stereoisomers have different effects?
What are the effects of chronic HHC use?

Common questions

Is HHC safe?

This rat study found low acute toxicity but dose-dependent anxiety and sensory processing impairment. There are no human safety studies, so the safety profile in people remains unknown.

How does HHC compare to THC?

HHC produced behavioral effects similar to THC, including reduced movement and impaired sensory gating. Its toxicity classification (Category 4) suggests moderate safety margins, but direct comparison studies are limited.

Read the original research

Hexahydrocannabinol: pharmacokinetics, systemic toxicity, and acute behavioral effects in Wistar rats.

The international journal of neuropsychopharmacology, 28(8)

View on PubMed ↗Publisher’s paper ↗

Citation

Šíchová, Klára; Mallarino, Barbara; Janečková, Lucie; Palivec, Petr; Vágnerová, Magdaléna; Vejmola, Čestmír; Nikolič, Marek; Ladislavová, Lucie; Mazochová, Kristýna; Ryšánek, Pavel; Šíma, Martin; Šafanda, Adam; Hiep, Bui Quang; Koutrouli, Isis Rita Anzel; Kuchař, Martin; Páleníček, Tomáš. (2025). Hexahydrocannabinol: pharmacokinetics, systemic toxicity, and acute behavioral effects in Wistar rats.. The international journal of neuropsychopharmacology, 28(8). https://doi.org/10.1093/ijnp/pyaf041