Chris explained on 17/06/2018 :
I'd like your
feedback and observations before I try this, though. AIUI, water does not
attack the active ingredient in question (diazepam) but light *does* so
provided I keep the fractions in light-tight bottles for not too long I
should be alright, provided I haven't overlooked anything. Have I?

How about a mortar and pestle, to powder the pills, then split the
powder by eye into 5 portions. Take 3 (=30%), or 4 (=40%).

Another way, might be to crush as above, then use a pair of those
scales that druggies use, to measure the dose accurately. The scales
are less than a tenner a pair from China.