Wa `alaykum As-Salamu waRahmatullahi wa Barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
Answering your question, the General Iftaa’ Department in Jordan, states the following:
Nicotine patches and all other medical patches don’t invalidate fasting because skin pores aren’t an open outlet to the coelom, and it is a condition that whatever invalidates fasting should enter from an open outlet, and this doesn’t apply to such medical patches because they contain therapeutic or chemical materials that send signals through the pores of the body and absorb them through blood capillaries of the skin.
After that, they enter the blood stream and circulate to the various parts of the body.
It was stated in Mughni al-Muhtaj , a Shafi`i book, that:
“Any material that enters the body through the skin doesn’t invalidate fast.”
This is the key idea of resolution No. 93(1/10), issued by the Islamic Fiqh Academy after reviewing the research papers concerning matters that invalidate fasting within the domain of medical treatment, along with consulting scholars and doctors.
The resolution reads as follows:
“Whatever enters the body through the skin, such as oils, ointments and therapeutic patches loaded with medical or chemical materials doesn’t invalidate fast.”
Allah Almighty knows best.