Why do remedies sometimes work, and then lose their effectiveness? I'm referring to the times when, after positive response with one remedy, increasing the dose of same fails it improve the situation. If you've truly hit upon the smilimum this would not happen.

So does this just mean the same problem has chnaged into one which will require a different remedy? If so, is cure really possible in these situations, or will the remedy required simply change indefinitely?

The remedies are loosing their effectiveness when the body is getting used with them. Like eating something you like very much but in time you are getting used to it and you don't like it as at the first bite.
Sometimes, the simillimum for a situation is in a particular dilution and it determin a change when it's a good dilution and frecvency in administration.
Also, it's a 'quantity' of need of the body to that remedy. Let's say it's like a cup which can be filled...
In my oppinion, the cure is possible with homeopathy help (if the person is changing - usually, the remedy is the trigger for the change).
We are living as an opened system, so, everytime we interact with something or someonelse, and we don't find a good way to adapt, we begin to disorganise ourselves and finally, we need new remedies
In conclusion, take right remedies only when you need them.

Dear Mogwai
Several reasons
1-the patient has perhaps antidoted himself
2-the wrong 'second' prescription potency its not always the next higher up potency
the vital force is tricky-it only resonates with certain potencies not all.
3-There might be a block-this could require a nosode
after the block has been removed continue the same remedy once again.
4-perhaps its nOT the well indicated remedy afterall.
Perhaps the immed. results were mere acute suppression and not a true path to cure.
Suppression "often" looks like "its getting better",symptoms are showing relief.(pain is gone,cough is gone...........etc)
A trained practicioner can tell the difference.................

__________________
"Great ideas often recieve violent opposition from mediocre minds"...................Einstein