As I understand it from various reports in the Press:
Kerry had 'funny turns' back in 1997, before she took any drugs, which might have been minor seizures/epileptic fits.
Her GP had her back for a check-up a fortnight after she started taking Zyban (to stop smoking). She told him that she'd had no problems. For some reason which nobody knows, Kerry didn't tell her GP that she'd passed out for 10-15 minutes on one occasion, had a 'funny turn' on another occasion, and she'd attended an emergency doctor for a check up.
It was not certain that she died of a seizure. Two doctors/patholgists disagreed about this. One said definitely not. The other said it was probable but he could not be certain.
The Coroner decided she had probably died of a seizure, but there wasn't enough evidence to be beyond reasonable doubt.
Chloroquine is a mild drug, has been around for years, and has a good safety record. In theory, it lowers your resistance to fits (which we all have) but the risk is so small that it is regarded as a safe drug and you can buy over the counter without a prescription.
Over-the-counter sleeping tablets (for example Nitol) also lower your resistance but the risk is so small you also don't need a prescription for it.
Zyban is a stronger drug, available onlt on prescription. It is still new, and doctors must only prescribe it with caution, safeguards and monitoring. Nobody knows why she told the GP she'd had no problems, when she had.
The Coroner had to mention all three drugs, because she'd taken three. But, IF she died of a seizure/fit, then Zyban is the one that's much newer, and still on the 'Caution' list.
It's still very much speculation whether Kerry actually had a fit, or sadly dropped dead for reasons which will never be known. About 5-8% deaths are of healthy people and the cause can't be discovered.