Does the Quran Cure all Illnesses?
Question

I have read in a fatwa that the Quran contains healing for both physical and mental illness. What is the evidence for that? And how can the Quran be used to heal baldness? May Allah reward you with good.
Praise be to Allah.The Quran is healing for all illnesses
The Quran is healing , as Allah, may He be exalted, says (interpretation of the meaning):
{And We send down of the Quran that which is healing and mercy for the believers, but it does not increase the wrongdoers except in loss.} [Al-Isra’ 17:82]
This includes both physical and mental illnesses. The Prophet (blessings and peace of Allah be upon him) used to recite al-Mu‘awwidhat [Surat Al-Falaq and Surat An-Nas] over himself and over any of his family who were ill; if that would not benefit them, he would not have done it.
Muslim (2192) narrated from `Aishah that when he was sick, the Prophet (blessings and peace of Allah be upon him) would recite al-Mu`awwidhat over himself and blow over himself . When his pain got worse, I would recite over him and wipe him with his own hand, seeking its blessing.
Muslim (2192) narrated that `Aishah said: “If one of his family fell sick, the Messenger of Allah (blessings and peace of Allah be upon him) would blow over him and recite al-Mu‘awwidhat. When he fell sick with his final illness, I started to [recite al-Mu`awwidhat and] blow over him and wipe him with his own hand, because it was more blessed than my hand.”
Ibn Hibban (6098) narrated from `Aishah that the Messenger of Allah (blessings and peace of Allah be upon him) came in when a woman was treating her or doing ruqyah for her , and he said: “Treat her with the Book of Allah.”
Ibn al-Qayyim (may Allah have mercy on him) said: 
“Allah, may He be exalted, says (interpretation of the meaning): {And We send down of the Quran that which is healing and mercy for the believers, but it does not increase the wrongdoers except in loss.} [Al-Isra’ 17:82]
The correct view is that the word min [translated here as ‘of’] refers to the entire Quran, and not only some of it. And Allah, may He be exalted, says (interpretation of the meaning):
{O mankind, there has to come to you instruction from your Lord and healing for what is in the hearts} [Yunus 10:57]
So the Quran is complete healing for all spiritual (mental) and physical diseases, and all ailments in this world and the Hereafter.
But not everyone is qualified or enabled to seek healing through it.
If the sick person seeks treatment in the Quran in the proper manner, and applies it to his illness with sincerity and faith, and complete acceptance, and firm belief, fulfilling the necessary conditions, the illness will never resist it.
How can illnesses resist the word of the Lord of earth and heaven Who, if He were to send His word down upon a mountain, it would cause it to crumble, and if He were to send it down upon the earth, it would cause it to break up?
There is no disease, spiritual or physical, but in the Quran there is an indication that refers to the cause and treatment of it, and how to protect oneself against it, for the one who is blessed with understanding of His Book." (Zad Al-Ma‘ad  4/322)
And he (may Allah have mercy on him) said in Zad Al-Ma‘ad (4/22): 
“The Prophet’s remedies for sickness were of three types:

Natural remedies
Divine remedies
Remedies composed of both.”

Then he (may Allah have mercy on him) said (4/162): 
“Section on the Prophet’s teachings on treating with Al-Fatihah one who has been stung by a scorpion.
It was narrated in As-Sahihayn that Abu Sa‘id al-Khudri said:
A group of the Companions of the Prophet (peace and blessings of Allah be upon him) set out on a journey and travelled until they came near one of the Arab tribes. They asked them for hospitality but they refused to show them any hospitality. Then the leader of that tribe was stung, and they tried everything but nothing helped him. Then some of them said: Why don’t you go to those people who are staying (nearby)? Maybe one of them will have something. So they went to them and said: O people, our leader has been stung and we have tried everything but nothing is helping him. Can any of you help? One of them said: Yes, by Allah; I can perform ruqyah for him. But, by Allah, we asked you for hospitality and you did not give us anything, so I will not perform ruqyah for him unless you give us something in return. So they agreed on a flock of sheep, then he started to blow on him and recite {Al-hamdu Lillahi Rabb il-‘Alamin….} [Al-Fatihah] Then he recovered immediately, like a hobbled camel released from its rope, and he got up and started walking, and there was nothing wrong with him. Then they gave them what they had agreed to, and some of them (the Companions) said: Let us share it out. The one who had performed ruqyah said: Do not do that until we come to the Prophet (peace and blessings of Allah be upon him) and tell him what happened, and we will wait and see what he tells us to do. So they came to the Messenger of Allah (peace and blessings of Allah be upon him) and told him what had happened. He said, “How did you know that it is a ruqyah?” Then he said, “You did the right thing. Share them out, and give me a share.”
Ibn Majah narrated in his Sunan from ‘Ali, who said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “The best medicine is the Quran .”
It is well known from experience that some words have particular effects and benefits, so what you think of the words of the Lord of the Worlds, the superiority of which over all other words is like the superiority of Allah over His creation, in which are complete healing, beneficial protection, guiding light, and all-encompassing mercy, and which, if they were to be sent down upon a mountain, it would crumble before His greatness and majesty.
Allah, may He be exalted, says (interpretation of the meaning):
{And We send down of the Quran that which is healing and mercy for the believers, but it does not increase the wrongdoers except in loss.} [Al-Isra’ 17:82]
The word min [translated here as ‘of’] refers to the entire Quran, and not only some of it. This is the more correct of the two scholarly views. This is like the verse in which Allah, may He be exalted, says (interpretation of the meaning):
{Allah has promised those who believe and do righteous deeds among them forgiveness and a great reward.} [Al-Fath 48:29] [It is known that] all of them are among those who believe and do righteous deeds. So what about the Opening of the Book (Al-Fatihah), the like of which was not revealed in the Quran or in the Torah or in the Gospel or in the Psalms? It contains all the concepts mentioned in the Books of Allah, as well as the most important and concise names of Allah: Allah, Ar-Rabb (the Lord), and Ar-Rahman (the Most Gracious); it affirms the Resurrection and mentions both types of Tawhid, namely Tawhid Ar-Rububiyyah (Affirmation of the oneness of divine lordship) and Tawhid Al-Uluhiyyah (affirmation of the oneness of divinity); and it mentions the need for the Lord, may He be glorified, in seeking help and in seeking guidance, which are to be sought only from Him, may He be glorified.
… There was a time when I was in Makkah and fell sick, and they could not find any doctor or medicine , so I started treating myself with Al-Fatihah. I would take some Zamzam water and recite Al-Fatihah over it several times, then I would drink it, and I made a full recovery as a result. Then I did that whenever I fell sick, and I benefitted greatly from it.”
Shaykh Ibn Baz (may Allah have mercy on him) said: 
“Allah, may He be glorified and exalted, has not sent down any disease but He has sent down a cure for it. Those who know it know it, and those who do not know it do not know it. Allah, may He be glorified and exalted, has created in what He sent down to His Prophet (blessings and peace of Allah be upon him), namely the Quran and Sunnah, a remedy for everything that people suffer from, both physical, mental and spiritual illnesses. Allah has benefitted people thereby, and much good has resulted from that, the extent of which no one knows except Allah, may He be glorified and exalted.” (Fatawa, 3/453)
How to treat physical sickness with the Quran
One of the ways of treating physical sickness with the Quran, that has been tried and tested, is writing some verses on a piece of paper, putting it in water , and seeking healing with that water:
Ibn al-Qayyim (may Allah have mercy on him) said: 
“A number of the early generations granted a concession which allows writing some verses of Quran and drinking them, and that is regarded as coming under the heading of the healing that Allah has created in the Quran.
Another example of that (i.e., treating the pains of childbirth) is to write [in Arabic] in a clean vessel the verses (interpretation of the meaning):
{When the sky has split [open],
And has responded to its Lord and was obligated [to do so],
And when the earth has been extended,
And has cast out that within it and relinquished [it],
And has responded to its Lord and was obligated [to do so].} [Al-Inshiqaq 84:1-5]
Then the pregnant woman may drink some of it, and some of it may be sprinkled on her belly.
To treat a nosebleed, Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) would write [in Arabic] on the patient’s forehead, {And it was said, “O earth, swallow your water, and O sky, withhold [your rain]” And the water subsided, and the matter was accomplished, and the ship came to rest on the [mountain of] Judiyy} [Hud 11:44] And I heard him say: I wrote it for more than one person, and they recovered. And he said: It is not permissible to write it in the blood of the nosebleed, as the ignorant do, because blood is impure (najis), so it is not permissible to write the words of Allah, may He be exalted, with it.
To treat a toothache, one should write [in Arabic] on the cheek that is on the same side as the pain: In the name of Allah, the Most Gracious, the Most Merciful, {Say, “It is He who has produced you and made for you hearing and vision and hearts; little are you grateful.} [Al-Mulk 67:23] And if you wish, you may write [in Arabic]: {And to Him belongs that which reposes by night and by day, and He is the Hearing, the Knowing.} [Al-An‘am 6:13]
To treat an abscess, one may write [in Arabic] on it:
{They ask you [O Muhammad] about the mountains. Say: My Lord will uproot them and scatter them as dust,
and He will leave the earth as a smooth, levelled plain,
in which you will see no depression or elevation} [Ta-Ha 20:105]” (Zad al-Ma`ad, 4:327-329)
Is there remedy for baldness in the Quran?
We have not come across any remedy for baldness in the Quran, but the matter is as discussed above: the Quran is healing. So if there is certain faith, resolve, and sincerity in turning to Allah, may He be exalted, then healing comes from Allah, the Lord of the Worlds, and by His will and decree, as is the case with all physical medicines with which people treat sickness. How often have people sought to treat sickness with physical medicine as prescribed by the most knowledgeable of physicians, but no healing results from it? But does this mean that this medicine cannot be a cause of healing, or does it cast aspersions on the knowledge of the physician?
And Allah knows best.