It means that half of the drug is gone in 3 weeks, then half of the remaining half is gone in another 3 weeks (so 75% in total is gone in 6 weeks), then half of what's left is gone in another 3 weeks etc etc. Does that make sense?

ETA: I will take a long time to be fully gone from your system, but depending on how sensitive you are to the dose, the effects of it will wear off quicker i.e. at 12 weeks, 6.25% of the original dose will remain, but you probably won't notice the therapeutic effect and will notice the withdrawal side effects (if any) before that point.

*Willow*