Setting: 1990s, non-descript setting but being a Brit the setting has a strong resemblance to North England.
Hello, I'm writing a murder mystery. One character has been delivering small doses of poison to her aging father in an attempt to make him dependent on her (He is 52 years old- this can go up, however, by 8 years or so if needs be).
Her father is a wealthy businessman, quite consumed in his work. His daughter, the poisoner, loves him dearly and so is not trying to kill him. I am looking for a poison that can be given in regular (you may take regular to mean anything from weekly to daily) doses and causing some illness, although not debilitating illness. It would be best if the symptoms could easily be confused with simply aging (i.e. general weakness, kidney problems, dizziness, forgetfulness etc.) or stress although I am prepared to work with other symptoms. The idea is her father is encouraged into early retirement due to what seems 'bad health'.
In order to make the symptoms just look like the effects of a worsening health complaint, it would also be good if the effects of the poison increase in severity as the residues of the poison accumulate in the body (here I understand it could be potentially lethal over time) - but this isn't entirely necessary, especially if it threatens my next point:
There should be no ever-lasting effects of the poison- once the doses have stopped being given, the victim needs to have the potential of a full recovery (give a suitable amount of time for the body rid itself of the poison). As previously mentioned the poisoner loves the victim and would not want them to suffer more than is necessary.
Finally, a time frame. In the first chapter, the victim dies (of a non-related cause) prior to signing over his company. By this point, the victim needs to have been suffering the symptoms for at least a fortnight - a month or two is more realistic to allow contracts to be drawn up, proposals to be made etc. The symptoms can go on for however much longer than this you want- as I said; he dies through a non-related cause. Depending on the poison you find, the actual poisoning process can have started up to 6 months prior (although feel free to adjust this date).
So in summary, in order of priority:
1. something that can be given in small, non-lethal doses over time.
2. The symptoms have been showing for 2-4 weeks
3. The victim can (potentially) recover fully once poisoning has stopped.
4. Mimics the effects of aging, stress etc.
5. Due to poison accumulating in the body, the effects worsen.