I was looking at my bottle of Ritalin this morning and I noticed it had an expiration date on it. I didnt know Ritalin could expire. What happens if you take it and it is expired? Will it not work or will you get sick? Im just curious of what will happen.

All meds have an expiration date. Meds become less effective over time.

If medications are kept cool dry and protected from light, most don't go "bad" - but lose some of their potency. Pharmacies should not be selling you anything that is too close to it's expiry date - not sure of the rules w.r.t. this, however.

Metronidazole becomes toxic after it expires. Aspirin never expires but it has an expiry date. But yeah, generally drugs lose potency with time. So expiry date has some relevence.