I was recently alarmed to find that my girlfriend has been taking what I consider to be an excessive dosage of diphenhydramine as a sleep aid. She has been averaging 30 25mg tablets a night (750mg). After doing some research online I came up with a number of answers for what is considered to be a safe dosage. One was 400mg/day, another was 700mg/day (I thought this number was high) another was 5mg/kg or 300mg for a 60kg person. In any case I am concerned that routinely taking this dosage (750mg) will damage her body, not to mention have negative psychoactive effects.