Does using nicotine patches on the shoulder invalidate fasting in Ramadan?

Patches do not invalidate the fast because they are like oil absorbed by the body, and what is prohibited is that which reaches the stomach. The ruling on their use depends on the extent of their harm; if their harm is proven, then their use is forbidden. Similarly, it should be considered whether the substance is an intoxicating narcotic, and it is not permissible to apply impurities to the body except out of medical necessity.