Man Experienced Nine Days of Cognitive Impairment After Eating HHC-C9 Cannabis Cookies | Research

The takeaway

A man in his early forties experienced nine days of cognitive and physical impairment after consuming cookies containing HHC-C9, a novel semisynthetic cannabinoid sold as a "legal high."

Consumers considering "legal" cannabis alternatives, emergency physicians, drug regulators.

9 days of cognitive impairment

What the researchers found

After eating two cannabis cookies labeled as containing 40 mg "CC9" and biting a gummy with unknown contents, a man in his early forties required emergency admission for deficits in alertness and responsiveness. He experienced vomiting, visual problems, and nine days of cognitive and physical impairment. Forensic toxicology confirmed HHC-C9, a novel semisynthetic cannabinoid.

Why it matters

Semisynthetic cannabinoids like HHC-C9 now account for over 40% of new psychoactive substances reported in Europe. They are sold as "legal highs" in convenience stores and online, often as cookies, candies, or vape products specifically targeting young consumers. This case demonstrates that their effects can be dramatically more severe and prolonged than natural cannabis.

The numbers in context

9 days of impairment. Two cookies consumed (labeled 40 mg CC9). Products often mislabeled and sold as souvenirs or potpourri. SSCs account for >40% of new substances at European level.

How the study worked

Single case report from an Emergency Department. Clinical presentation documented alongside forensic toxicological analysis confirming HHC-C9 in blood.

What this study cannot tell us

Single case report. Co-ingestion of gummy with unknown contents. Cannot determine exact dose consumed. Individual susceptibility may vary. Limited information on HHC-C9 pharmacology.

How to read the evidence

Preliminary: single case report providing important clinical alert about a novel compound.

When this study was published

2025 study

The bigger picture

The proliferation of semisynthetic cannabinoids through legal loopholes creates a growing public health risk. These products are designed to mimic THC but can produce much stronger and longer-lasting effects. The nine-day impairment in this case far exceeds anything expected from natural cannabis, highlighting the unpredictability of these novel compounds.

Questions still open

How common are severe reactions to HHC-C9? Should emergency departments routinely test for semisynthetic cannabinoids? What regulatory approaches could address the rapid emergence of new synthetic variants?

Common questions

What is HHC-C9?

It is a semisynthetic cannabinoid designed to mimic THC effects. It is sold in edible products like cookies and gummies, often marketed as a legal alternative to cannabis. This case shows its effects can be dramatically more severe and prolonged than natural cannabis.

Are "legal" cannabis cookies safe?

This case demonstrates they can cause serious, prolonged effects. The man experienced nine days of cognitive and physical impairment from products sold as legal alternatives. These products often bypass regulations by being mislabeled.

Read the original research

Long-Lasting Cognitive and Physical Impairment After Recreational Use of the Semisynthetic Cannabinoid Hexahydrocannabinonyl (HHC-C9): A Case Report.

Reports (MDPI), 8(3)

View on PubMed ↗Publisher’s paper ↗

Citation

Reiter, Nanna; Palmqvist, Dorte Fris; Larsen, Gro Borges; Høi, Mathilde Emilie; Rasmussen, Brian Schou; Thomsen, Ragnar. (2025). Long-Lasting Cognitive and Physical Impairment After Recreational Use of the Semisynthetic Cannabinoid Hexahydrocannabinonyl (HHC-C9): A Case Report.. Reports (MDPI), 8(3). https://doi.org/10.3390/reports8030176