Medicine half life

A short challenge concerning the decay of medicines in the body.
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Problem

A certain medicine is broken down by the body so that half of the remaining dose in the system is broken down every 12 hours. 

If I regularly take 400mg of medicine in the morning and 400mg of medicine in the evening what is the long term effective level in my system after I take each tablet?

 

Extension: What will be the long term stable level after I take each tablet if the body breaks down half of the remaining dose every 6 hours?

 
Did you know ... ?

The 'half-life' of medicines is an important concept in medicine, particularly in the area of anti-depressants which take some time to reach active levels in the body.