1g of caffeine? That's like 25 cups of espresso. Have you had a cardiologic exam beforehand?
So yeah, two freaking massive 20oz pours of highly caffeinated coffee will get you to around 1 gram.
But FWIW the daily recommended dose is 400mg. 1g is a ton of caffeine and way beyond what you would get to by sipping on coffee throughout the day (it's 10+ cups of drip).
I cannot find where the number originates, but there is at least one study @ https://www.sciencedirect.com/science/article/pii/S027869151... which explicitly claims "vidence supported consumption of ≤400 mg/day in adults is not associated with overt, adverse effects."
[1] Counter-intuitive I know, but it seems to help - it makes the intrusive thoughts easier to ignore