Don't know, but if somebody was tampering with my food, I'd be talking to the police...
If he is contaminating your food with diabetic drugs, the effect depends on what he's contaminating them with. What's your GP said about your blood sugar? Has it been high/low - it seems to be erratic but how high/low? That's me being nosey really because whatever your answer, my original comment still stands, if I thought somebody was maliciously tampering with my food, I'd be talking to the police.