How we built a medicine-substitution engine that refuses to be clever
There is a category of bugs where the code looks perfectly correct in code review, the unit tests pass, the demo on stage goes beautifully, and a real person dies.
Medicine substitution is one of them.
We built Agada — point a phone camera at a medicine strip in India, and the app tells you whether the drug is registered with the regulator, what it does, and whether a chemically identical version is available at the government pharmacy for a fraction of the price. The point is real: Indians spend about ₹65,000 crore a year out of pocket on branded medicines when the same molecule sits in a Jan Aushadhi Kendra at a tenth of the cost. The Dolo-650 story (₹32 vs ₹4.90 for the same paracetamol) is the most famous example, not the only one.
The hard part isn't the camera, the OCR, or the price lookup. The hard part is the substitution engine — the piece of code that decides "is this salt the same as that salt." Get that wrong in the wrong direction, and the app cheerfully tells a user that their 500mg anti-epileptic can be replaced with a 200mg one, because the strings look similar.
