"Some studies indicate that under certain circumstances, CBD acute anxiolytic effects in rats were reversed after repeated 14-day administration of CBD.2 However, this finding might depend on the used animal model of anxiety or depression. This is supported by a study, where CBD was administered in an acute and “chronic” (2 weeks) regimen, which measured anxiolytic/antidepressant effects, using behavioral and operative models (OBX=olfactory bulbectomy as model for depression).18 The only observed side effects were reduced sucrose preference, reduced food consumption and body weight in the nonoperated animals treated with CBD (50 mg/kg). Nonetheless, the behavioral tests (for OBX-induced hyperactivity and anhedonia related to depression and open field test for anxiety) in the CBD-treated OBX animals showed an improved emotional response. Using microdialysis, the researchers could also show elevated 5-HT and glutamate levels in the prefrontal cortex of OBX animals only. This area was previously described to be involved in maladaptive behavioral regulation in depressed patients and is a feature of the OBX animal model of depression. The fact that serotonin levels were only elevated in the OBX mice is similar to CBD differential action under physiological and pathological conditions.
"A similar effect was previously described in anxiety experiments, where CBD proved to be only anxiolytic in subjects where stress had been induced before CBD administration. Elevated glutamate levels have been proposed to be responsible for ketamine's fast antidepressant function and its dysregulation has been described in OBX mice and depressed patients. Chronic CBD treatment did not elicit behavioral changes in the nonoperated mice. In contrast, CBD was able to alleviate the affected functionality of 5HT1A receptors in limbic brain areas of OBX mice.18 and references therein
"Schiavon et al. cite three studies that used chronic CBD administration to demonstrate its anxiolytic effects in chronically stressed rats, which were mostly mediated via hippocampal neurogenesis.19 and references therein For instance, animals received daily i.p. injections of 5 mg/kg CBD. Applying a 5HT1A receptor antagonist in the DPAG (dorsal periaqueductal gray area), it was implied that CBD exerts its antipanic effects via these serotonin receptors. No adverse effects were reported in this study."
Iffland, Kerstin, and Franjo Grotenhermen. “An Update on Safety and Side Effects of Cannabidiol: A Review of Clinical Data and Relevant Animal Studies.” Cannabis and cannabinoid research vol. 2,1 139-154. 1 Jun. 2017, doi:10.1089/can.2016.0034