Memantine: what an 80-hour half life means for choosing an effective dosage

After reading lots of memantine anecdotes and trying to figure out why so many reviews are great at first and then turn into horror stories, I have an idea what's going on.

Many medications require a certain blood level to be effective. Some reviewers have referred to a U-shaped effectiveness curve for memantine, where too much or too little don't work, but the right amount works well. However, instead of considering the blood level that works well, people try to guess a dosage, which, due to the 80-hour half-life of memantine, makes it very likely that they will overshoot the effective level so quickly that they barely notice it, and rapidly descend down the "overmedicated" side of the u-shaped effectiveness curve, with headaches, brain fog, fatigue, psychotic breaks, what have you.

I set up a half-life spreadsheet which told me this: For a substance with an 80-hour half-life, 3 full days (72 hours) after the first dose, 53% of that first dose is still in my system. In addition, 66% of the second dose is still in circulation and 81% of the third dose. Calling the first dose "dose 0", day 3's dose is dose 4. After dose 4, taken at 72 hours, my cumulative level rises to al…