I’m confused about caffeine pills.

Vivarin (200 mg), pic related and as of recent drug of choice works way better for me than off brand tablets. Feels like ~8 hours of energy. Then a big crash.

Tried many off-brand caffeine tablets, even double dose. Mostly just headaches though and not the same “clean” alertness.

I assumed quality control or additives or what not. But it’s literally just caffeine, right? Do other people see this?
Could tablet fillers / how fast it dissolves matter? Or is this just tolerance + timing + placebo?

What’s the actual mechanism here?

Vivarin is the first time I understand why some people call it poor people's meth...

placebo effect?

Add pic of ingredients

Active Ingredients: Caffeine (200 mg), Alertness Aid.

Inactive Ingredients: Carnauba Wax, Colloidal Silicon Dioxide, Croscarmellose Sodium, D&C Yellow 10 Aluminum Lake, Dicalcium Phosphate Dihydrate, FD&C Yellow 6 Aluminum Lake, Hypromellose, Magnesium Stearate, Microcrystalline Cellulose, Polyethylene Glycol, Polysorbate 80, Starch , Titanium Dioxide

So unless one of those "inactive ingredients" is actually not so inactive (I don't know what they all are), it sounds like probably quality control and/or timing and/or placebo.

Off-brand caffeine tablets are unregulated, but Vivarin is FDA-approved. My guess is it's mostly down to quality / quality control.

Tolerance wouldn't factor in if you're taking supposedly-equal doses of other brands yet experiencing a weaker effect.