I suppose it's due to an overdose,, I looked it up and apparently taking too many calcium channel blockers (which is what adblocker is) can slow your heart rate and lower your heart pressure, which can lead to your heart stopping altogether. I wouldn't exactly call it the most reliable method though.
I got the info from this,, maybe it can help:
https://en.wikipedia.org/wiki/Calcium_channel_blocker_toxicity