[richardwigley]

So the op has stopped drinking coffee and was clear of headaches which he thinks is due to Dandy Blend.

However, he is still getting a considerable fraction of the caffeine he got previously, but now from tea. If he is still taking the active drug, Caffeine, why would he expect any withdrawal?

[draebek]

Agreed. I think black tea, in particular, can have like 75% of the caffeine in the same quantity of coffee. See, for example, the table at https://en.wikipedia.org/wiki/Caffeine#Natural_occurrence

[wordbank]

There's obviously some difference in metabolism of caffeine from coffee and from tea.

I drink 3-4 huge 0.5L cups of green tea during the day and it has no energizing effect. I rarely drink coffee but when I do, it energizes me a lot.