I end up biting a lot of pills to get around that dose. I definitely always felt groggy until I dialed down the dose to just right, and it works perfectly: I fall asleep far quicker and more assuredly, and I don't feel to groggy. I can't believe they sell pills as large as they do, what other medication varies in dosage as much?
Vitamin B12 supplements can be found in a range covering about 4 orders of magnitude. The RDA is 2.4 ug/day and the Costco daily multivitamin provides 6mcg, but here is someone selling 10,000 ug supplements: https://www.hartzells.com/b-12-10000mcg-90960
It's easy to find any other order of magnitude between those if you like. A half-pound of beef liver would give you about 186 ug.
I suspect the dosage and absorption isn't fully understood yet or very individual. For me some 2mg pills work fine and other 3mg pills don't; currently I use 4mg time-release and it's mostly fine. 1 mg is definitely not enough for me.
I would be groggy a few hours after taking the pill but not in the morning.
Since they're not regulated as medication, melatonin pills have no guarantees about actual melatonin content. In studies, the vast majority of supplement labels are inaccurate.
Would it not be easier to not drink so much caffeine late in the day? Unless you're jetlagged, there's not much evidence AFAIK that melatonin will induce sleep better than a placebo.
Not OP, but I’ve had horrible sleep over the past year. I had taken melatonin a while back before stopping, so on a whim, I decided to bite off a bit of one of my old 5mg pills before sleep. Didn’t give it any second thought — didn’t even think it would do anything. But I slept like a baby for the first time in months. And it’s completely reproducible.