Female Rats Work Harder for THC Vapor, and Prior Exposure Increases Use | Research

The takeaway

In a new THC vapor self-administration model, female rats responded more for THC than males, and pre-exposure to THC significantly increased later self-administration.

Addiction neuroscience researchers, sex-differences in substance use researchers, animal model developers

Female rats worked harder for THC vapor; pre-exposure increased later self-administration

What the researchers found

Among 96 rats, both males and females voluntarily self-administered THC vapor over several months. Female rats responded more than males as the effort required increased. Prior THC vapor exposure significantly increased later self-administration, suggesting sensitization. Rats titrated their intake based on THC concentration.

Why it matters

This model closely mirrors human cannabis inhalation behavior and reveals important sex differences and sensitization effects that could inform understanding of why some people develop cannabis use disorder.

The numbers in context

N=96 rats (6-12 per sex/group). Training dose: 50 mg/mL THC. Dose range tested: 50-200 mg/mL. Female rats responded more at FR4-5 schedules. THC pre-exposure increased subsequent self-administration.

How the study worked

Controlled animal study with 96 Sprague Dawley rats (male and female) pre-exposed to THC or vehicle vapor, then trained to self-administer THC vapor under increasing effort requirements and varying concentrations.

What this study cannot tell us

Animal models cannot fully replicate human cannabis use behavior. Propylene glycol vehicle may have its own effects. Limited to one strain of rats. Short pre-exposure period may not reflect human use patterns.

How to read the evidence

Well-designed animal study with novel vapor delivery model, but translational gap to human cannabis use remains significant.

When this study was published

2025 study establishing a novel THC vapor self-administration model.

The bigger picture

The sex differences found here parallel human data showing women may progress to cannabis use disorder faster. The pre-exposure sensitization effect has implications for understanding how early cannabis use might facilitate later problematic use.

Questions still open

What drives the sex difference in THC reinforcement? Does the sensitization effect have a critical window? Could these findings inform sex-specific treatment approaches?

Common questions

Do males and females respond differently to THC?

In this rat study, females worked significantly harder to obtain THC vapor as the effort required increased, while males did not show the same escalation. This parallels human findings suggesting sex differences in cannabis reinforcement.

Does early cannabis exposure increase later use?

Rats pre-exposed to THC vapor consumed significantly more THC when later given the opportunity to self-administer, suggesting that early exposure may sensitize the brain's reward system to cannabis.

Read the original research

Effects of sex and pre-exposure on Δ9-tetrahydrocannabinol (THC) vapor self-administration in rats.

Psychopharmacology

View on PubMed ↗Publisher’s paper ↗

Citation

Moore, Catherine F; Weerts, Elise M. (2025). Effects of sex and pre-exposure on Δ9-tetrahydrocannabinol (THC) vapor self-administration in rats.. Psychopharmacology. https://doi.org/10.1007/s00213-025-06930-8