Please could someone explain...
 

I don't understand what a half-life means regarding meds.

half life
 

Hi Faith

Half life measures how long it takes for half of the drug to clear
from your blood. The longer the half life, the longer the drug
stays in your blood.

Hope this helps.

I'll try.
If a substance has a half life of 7 days and you start out with a concentration of 100 per ml.
After 7 days the concentration will be: 50 per ml
after 14 days the concentration will be: 25 per ml
after 21 days the concentration will be 12 1/2 per ml
sfter 28 days the concentration will be 6 1/4 per ml

Each 7 day period will reflect a 50% less concentration than the week before.

Regards
Joe