BACKGROUND AND PURPOSE: Consumption of Synthetic Cannabinoid Receptor agonists (SCRAs) is associated with severe adverse reactions including seizures, arrhythmias and death, but the molecular mechanisms surrounding SCRA toxicity are not yet established. These disease-like symptoms are also synonymous with altered T-type calcium channel activity which controls rhythmicity in the heart and brain. This study examined whether SCRAs alter T-type activity and whether this represents a possible mechanism of toxicity. EXPERIMENTAL APPROACH: Fluorescence-based and electrophysiology assays were used to screen 16 structurally related synthetic cannabinoids for their ability to inhibit human T-type calcium channels expressed in HEK293 cells. The most potent compounds were then further examined using patch clamp electrophysiology. KEY RESULTS: MDMB-CHMICA and AMB-CHMINACA potently blocked CaV3.2 with IC50 values of 1.5 and 0.74 μM respectively. Current inhibition increased from 47 to 80% and 45 to 87% respectively when the channel was in slow-inactivated state. Both SCRAs had little effect on steady state inactivation, however MDMB-CHMICA significantly shifted the half activation potential by -7mV. Neither drug produced frequency dependent block, in contrast to the phytocannabinoid Δ9-THC. CONCLUSIONS and IMPLICATIONS: SCRAs are potent agonists of CB1 receptors and can be extremely toxic, but observed toxicity also resembles symptoms associated with altered CaV3.2 activity. Many SCRAs tested were potent modulators of CaV3.2, raising the possibility that SC toxicity may be due in part to CaV3.2 modulation. This potent T-type channel modulation suggests the possibility of SCRAs as a new drug class with potential to treat diseases associated with altered T-type channel activity. ### Competing Interest Statement The authors have declared no competing interest.

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