Are Lidoderm patches dangerous to use after expiration date even if sealed in their packages?

No they are not,they might lose of its potency,but they won’t be harmful to you

No, not dangerous. It might not be quite as effective but it's not going to cause any side effects or anything. The expiration dates on lidocaine patches are there because the drug starts to lose efficacy after a while. It just starts to break down chemically but there's a grace period there and they actually last for some time after that date but you really should use the fresh patches to get the most relief you can.