Enquiring minds apparently want to know... Two people have written me in the last few days to see if my use of diphenhydramine as a sleep aid is still working. Short answer: yes it is, just as well as when I started several months ago. I've settled on a dose of 12.5 mg (I chop 25 mg pills in half). When I can remember (that's infrequently :) to take it an hour or so before I go to bed, that dose is darned near perfect. With more experience, I have a better idea of why it works for me. I wake up nearly every night sometime between 1 am and 2:30 am. Before I started using diphenhydramine, there was an excellent chance (at least 3 of 5 nights) that I would not go back to sleep. Since I've started the diphenhydramine regimen, I go back to sleep almost every night. I'm now regularly getting between 7 and 8 hours of sleep every night, and occasionally getting even more (one memorable night a couple of weeks ago I slept for 10 hours – and if that doesn't seem remarkable to you, it certainly is to me!).
I haven't seen any side effects yet at this dose. If I take even slightly more (like 15 mg) I start to have “morning sedation” – well-described in the list of side-effects for diphenhydramine. That's a groggy state that caffeine and a shower won't wake me up from – I have to just let it wear off, which can take several hours. At even higher doses, the morning sedation is deeper and longer lasting. I've tried 10 mg doses, which seems insignificantly different than the 12.5 mg dose I've settled on – and it isn't reliable in letting me fall back asleep in the middle of the night. I'm surprised at the sensitivity of the dosage, but there it is.
Last night is a good example of my experience with this drug. I took my 12.5 mg dose just before I took my evening shower at 9 pm. I took my shower, went to bed, read for a while, and was lights-off and ready to sleep at 10:15 pm. I woke at 1 pm, went back to sleep within a few minutes. I woke up at 5:15 am, got up and felt almost no morning sedation. By the time I took my shower and had my morning tea, I was wide awake. This sort of thing may be normal for most people, but for me it's still quite novel. :)