What is the ruling on taking medication to treat insomnia, and what is its legitimate (Shar’i) treatment?

It is permissible to take sedatives for insomnia, with a doctor's consultation, as long as it does not result in predominant harm. As for the prophetic guidance in this matter, it is through supplication (du'a) and remembrance of Allah. Ibn al-Qayyim mentioned the hadith (definition) narrated by al-Tirmidhi from Buraydah, that Khalid complained of insomnia to the Prophet, whereupon the Prophet said to him: "When you go to bed, say: 'O Allah, Lord of the seven heavens and what they overshadow, Lord of the seven earths and what they carry, and Lord of the devils and those whom they lead astray, be my protector from the evil of all Your creation, lest any of them should transgress against me or oppress me. Mighty is Your protection, and exalted is Your praise, and there is no god besides You.'"