I made the mistake of thinking that if 450mg was good, 900mg would be twice as good. This is not how valerian works.
At 900mg, taken 45 minutes before bed, I experienced: noticeable stomach discomfort (not quite nausea, but a gurgling, crampy feeling in my upper abdomen), a headache that started within an hour and persisted through the night, and paradoxically -- more wakefulness, not less. I lay in bed feeling physically uncomfortable and mentally alert for over two hours before finally falling asleep.
I tried this dose three consecutive nights thinking maybe I needed to adjust. All three nights produced the same pattern: stomach upset, headache, and a wired, slightly anxious feeling that was the opposite of sedation.
I dropped back to 450mg and the negative effects disappeared. At the lower dose, valerian works well for me -- gentle sleepiness, no stomach issues, no headache.
The lesson: with valerian, more is not better. The dose-response curve seems to plateau or even reverse at higher doses. The 300-600mg range that most studies use exists for a reason. If you are not getting results at 600mg, doubling the dose is not the answer -- you are probably a non-responder and should try a different approach.
I also wonder if the paradoxical stimulation at high doses relates to the lipophilic valerian compounds (isovaltrate) that are inverse agonists at adenosine receptors. Higher doses extract more of these compounds, which could theoretically counteract the sedative effects. Just speculation, but it would explain the pattern.