These substances are not inherently forbidden: a scientific phrase that floats around is "The dose makes the poison". Ironically there is a hadeeth which explicitly nullifies that phrase; and another hadeeth that states "I was given the quran, and a hadeeth like it" despite the quran stating there is nothing like God's words, the best of hadeeth.
It is apparent that this destructive delusion has carried over into "quranist" thinking. God placed all substances on Earth for a defined purpose; they can all be used for goodness and badness.
In this case no, it is not forbidden to do such and such. Do as you please. The command is explicit: avoid intoxication, avoid satan, avoid mischief, avoid any evil conduct which is a direct effect of consuming any substances.
However have you ever given thought to the root cause of your symptoms? Muscle tensions, harbouring resentment, anger, arrogance, hard-heartedness, despairing in God, all sorts of spiritual illnesses result in chronic symptoms. It takes a meditative mind to piece apart one's life and observe the true cause of your illness; and certainly a man in a white coat could not tell you even if he had spent 200 years in medical school learning and learning. They do try, yet they fail relentlessly without exception. This is because the mind of man can be deceived by garnished desires for profit and greatness whether those desires originate from that soul or whether that soul is under the spell of other shayateen who seek to cause strife for their own temporary gain.
Throwing painkillers at such a thing will impede your spiritual progress and turn you away from God, and detach you from your individual sovereignty. God did not make us defective creatures, for each set of genetics there is a complementary environment in which those genes come to absolute fruition and reach their best potential; even what you would consider genetic "disorders" such as Downs syndrome. God does not make mistakes. Review your diet, review your activity levels, look deep within at all your emotions, repressed and surfaced. You shall be surprised by what you find. When you find the true source and make the necessary lifestyle change, all illnesses dissolve of their own accord.
