What doses or active compounds in damiana could reach the brain?

Damiana's own compounds have never been measured in human blood or brain here. The only damiana record is a lab dish, not a body.

The one damiana study in front of me isolated pinocembrin, acacetin, apigenin 7-glucoside and Z-echinacin and measured how strongly they block aromatase, an enzyme, in a test tube [4]. That tells you the molecules exist and are biologically active. It tells you nothing about how much survives the gut, enters the blood, or crosses into the brain. No dose, no plasma level, no brain measurement.

The closest thing to a brain-relevant number comes from other plants. Flavonoid glycosides like these absorb poorly: hyperin reached only about 1 in 100 of the dose in mouse blood [2], and quercetin in dogs was about 4 in 100 bioavailable, with most of what circulates being conjugated, meaning chemically tagged and altered [3]. A niosomal ginkgo formulation did push measurable extract into rat brain [1], but that is an engineered carrier, not a tea.

So the honest answer to "what dose reaches the brain" is that nobody has measured it for damiana. The chemistry says the likely actors are pinocembrin and acacetin [4], and the absorption data from cousin flavonoids says most of an oral dose never makes it into blood intact [2][3]. A tea delivers a small, variable amount on top of that.

My call: no human or animal study here shows any damiana compound reaching the brain, and the flavonoid absorption data makes a large brain dose unlikely from tea. Confidence: low, because the pharmacokinetic study that would settle it has not been done in front of me.