In the original Fallout's Mentats were intended to be ADHD medication. (As some may know they decided to change names from real world meds after the whole morphine/med-x thing.) Concidering how it works I'd say it is Methylphenidate.
Assuming that here would be how Mentats are prescribed in an average adult.
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 Overdose happens if exceeding 60mg per day
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 Immediate Release Tablets each will last 3-4 hours. (6-8 minutes ingame)
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 They are taken 3 times daily (typically 20-30 minutes before meals)
The tin if unopened would contain four one week sheets. Each sheet would be 21 tablets, leading to 84 uses a tin.
Proposed fix for imbalances:
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 The value could be raised to 1680 caps/sm chips and drop by 20 caps each use.
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 The tins could place random amounts of tablets in the players inventory. In example they could act like coin purses in Skyrim.
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 Possibly make the ones in OWB drop less.
