Long-term effect of oral cannabidiol administration to healthy adult dogs on tear production, intraocular pressure, and tear concentrations.

Objective: To determine the chronic effects of oral cannabidiol (CBD) use on tear production, intraocular pressure (IOP), and concentration of CBD in tears of healthy dogs.

Animals studied: Eighteen healthy research Beagles.

Procedures: This was a masked, placebo-controlled, randomized prospective study. Eighteen dogs were randomly assigned to three groups (six dogs per group) based on daily dosage of oral MCT oil (placebo), CBD 5 mg/kg, and CBD 10 mg/kg. Schirmer tear test (STT-1) and IOP were measured twice daily (7 am and 7 pm) every 4 weeks for 36 weeks. Week 36 tears were collected and analyzed for CBD concentrations (ng/mL) using liquid chromatography/mass spectrometry. A mixed linear model was used as the statistical method and p-value <.05 was considered significant.

Results: No significant differences were found between placebo vs. 5 mg/kg vs. 10 mg/kg for STT-1 or IOP (AM and PM). CBD was detected in 10 out of 11 (91%) viable tear samples receiving 5 mg/kg or 10 mg/kg dosages. One sample in the 5 mg/kg group had inadequate tear volume for analysis. The CBD concentration in tears was at or below the lower limit of quantification in placebo group, 4.12-11.2 ng/mL for the 5 mg/kg group, and 6.22-152 ng/mL for the 10 mg/kg group.

Conclusions: Long-term administration of oral CBD in healthy research beagles demonstrates a favorable safety profile regarding ocular tolerability. Oral CBD administration does not appear to affect tear production or IOP over a 36-week period. This is the first canine study positively identifying concentrations of CBD in tears following oral administration.