I thought that Drs were only allowed to prescribe 1 month's worth at a time. I heard that one of the reasons were incase meds need to be changed to another type, so the rest of the month's worth is better ditched than 6 months IYSWIM.
Even if you haven't broken into the boxes of meds and hand them back to the phamacy, they then have to dispose of them. The pharmacy can't take the risk of giving someone else those same meds in case they have been tampered with. I understand that not many people will tamperd with excess medication, but the pharmacies can't take that risk.
The other thing is overdose. Hospitals are more able to treat an overdose of 1 month's worth of tablets, than 6 months. A patient is less likely to recover from ingesting 6 months of sertraline, than a patient with 1 month of sertraline in them.
WRT paracetamol, a relatively small amount can cause liver damage. Lets say that person A takes 5 paracetamol and ends up with severe liver damage that cannot be repaired. Now AFAIK, although I could be wrong, the same amount of sertraline is more likely to be treated effectively with better outlook and less damage to the liver IYSWIM.
Don't be afraid to correct me if I'm wrong though. I'm always told I'm wrong and always get the blame for everything
. My motto should be accept and move on 
Anyway, have decided to have a cuppa, so anyone want a
and some homemade chocolate cake with chocolate fudge icing?
I think MNHQ should make a drooling emoticon. Who's with me on that one 