The word "Ruqya"
The Arabic word ruqya (رُقْيَة) linguistically refers to a verbal incantation or chant, uttered or written, to remove unwanted afflictions like possession and sickness. The plural of ruqya is ruqa (رُقَى).
In normal usage, the word is used to refer to the process of expelling jinn from possessed persons, objects and places, and curing evil eye and non-spiritual illnesses and injuries with religious statements, practices and artefacts where medical treatment fails.
The practitioner of ruqya is called Raqi (رَاقِي), the plural of which is Ruqat (رُقَاة).
Validity & Conditions
All forms of ruqya are permissible so long as it does not violate Islamic Law. The Prophet (ﷺ) said:
لَا بَأْسَ بِالرُّقَى مَا لَمْ يَكُنْ فِيهِ شِرْكٌ
All types of ruqya are fine so long as they contain no shirk (polytheism). [Muslim]
إِنَّ اَللَّهَ لَمْ يَجْعَلْ شِفَاءَكُمْ فِيمَا حَرَّمَ عَلَيْكُمْ
Allah did not make your cure in what He made unlawful to you. [Al-Bayhaqi]
Also, Ibn Hajar reported ijma' (consensus among all scholars) that ruqya must satisfy the following three conditions:
The words are Islamic. For example, Quran, dhikr and du'a.
The words are comprehensible. Language or words that are not intelligible are disallowed.
Those taking part in the ruqya must believe that Allah alone cures and causes the words to have an effect.
Conditions for the effectiveness of the treatment
In order for the ruqya treatment to be effective, both the patient and the raqi must satisfy spiritual, legal and social conditions:
Expectation of cure from Allah alone
Intention for the cure to take effect through the ruqya treatment
Correct practice of ruqya treatment
Mental and emotional stability of the patient
Consistency in adhering to the ruqya treatment
Support to the patient by family and friends
Refraining from sin