Once the old substances patent expires, any drug company can produce generics. There is no incentive to ignore patents and produce generics if the patent is expired because other companies will likely be producing generics, assuming there is actually a market for the drug.
> Once the old substances patent expires, any drug company can produce generics.
Except for when the company makes a tiny modification to the drug that doesn't change its effectiveness and files for a renewed patent, like in the Novartis suit that India's Supreme Court recently (and rightfully) rejected.
That's not the way patents work. There is not a renewal, but a new patent on the modified substance. The patent on the original substance would still expire. This, of course, raises an interesting question. If the claim is that the tiny modification doesn't change the drugs effectiveness, why not produce the original substance with the expired patent (or purchase a generic from a pharmaceutical that is already doing just that)?
Their actions seem to suggest that they do believe the modification increases the drugs effectiveness, but they don't want to pay for any of the R&D behind that.