Short answer
Yes, if fasting would make your illness worse, slow your recovery or cause you serious harm. You make up the missed days when you are well. If the illness is permanent and you will never be able to fast, you pay fidya instead. A minor cold or headache is not normally an excuse.
A sick person may leave the fast when there is a strong likelihood of harm, known from clear signs, personal experience, or the advice of a competent, trustworthy Muslim doctor. The missed days are made up later with no fidya. Someone with a permanent illness and no hope of recovery pays fidya for each day instead.
The four schools agree on this.
Explanation
Allah names illness as one of the two main excuses for not fasting in Ramadan, and says He wants ease for you, not hardship. The four schools agree on the principle: an illness that fasting would worsen, prolong or make dangerous permits not fasting, with the days made up later.
What counts. The test is real harm, not mere discomfort. Examples where people are usually excused include insulin-treated diabetes with a risk of low blood sugar, kidney disease, recovery from surgery, a high fever, and treatments that must be taken at set times during the day. A mild cold, a headache or ordinary tiredness is not enough on its own.
How you know. The Hanafi texts accept clear signs, your own past experience of the same illness, or the advice of a competent and trustworthy doctor, preferably a practising Muslim who understands why the question matters. A vague fear with no basis is not enough.
- If illness starts during a fast, you may break it and owe qada only.
- Ask your doctor whether medicines can be moved to suhoor and iftar.
- Make up the days whenever you are well; see when to make up missed fasts.
- Permanent illness: pay fidya; see what is fidya.
Every illness is different, so speak to a qualified mufti together with your doctor about your own case. Specific medicines are covered in injections and drips and inhalers.
Ask a mufti about your own case. This answer explains the general ruling. When the details of your situation matter, as they do here, ask a qualified mufti and give them the full facts. Where to ask a scholar.
The evidence
Quran, Surah Al-Baqara 2:184
أَيَّامًۭا مَّعْدُودَٰتٍۢ ۚ فَمَن كَانَ مِنكُم مَّرِيضًا أَوْ عَلَىٰ سَفَرٍۢ فَعِدَّةٌۭ مِّنْ أَيَّامٍ أُخَرَ ۚ وَعَلَى ٱلَّذِينَ يُطِيقُونَهُۥ فِدْيَةٌۭ طَعَامُ مِسْكِينٍۢ ۖ فَمَن تَطَوَّعَ خَيْرًۭا فَهُوَ خَيْرٌۭ لَّهُۥ ۚ وَأَن تَصُومُوا۟ خَيْرٌۭ لَّكُمْ ۖ إِن كُنتُمْ تَعْلَمُونَ ﴿١٨٤﴾
[Fasting for] a limited number of days. So whoever among you is ill or on a journey [during them] - then an equal number of days [are to be made up]. And upon those who are able [to fast, but with hardship] - a ransom [as substitute] of feeding a poor person [each day]. And whoever volunteers excess - it is better for him. But to fast is best for you, if you only knew.
The sick person may leave the fast and make up the same number of days later.
Quran, Surah Al-Baqara 2:185
شَهْرُ رَمَضَانَ ٱلَّذِىٓ أُنزِلَ فِيهِ ٱلْقُرْءَانُ هُدًۭى لِّلنَّاسِ وَبَيِّنَٰتٍۢ مِّنَ ٱلْهُدَىٰ وَٱلْفُرْقَانِ ۚ فَمَن شَهِدَ مِنكُمُ ٱلشَّهْرَ فَلْيَصُمْهُ ۖ وَمَن كَانَ مَرِيضًا أَوْ عَلَىٰ سَفَرٍۢ فَعِدَّةٌۭ مِّنْ أَيَّامٍ أُخَرَ ۗ يُرِيدُ ٱللَّهُ بِكُمُ ٱلْيُسْرَ وَلَا يُرِيدُ بِكُمُ ٱلْعُسْرَ وَلِتُكْمِلُوا۟ ٱلْعِدَّةَ وَلِتُكَبِّرُوا۟ ٱللَّهَ عَلَىٰ مَا هَدَىٰكُمْ وَلَعَلَّكُمْ تَشْكُرُونَ ﴿١٨٥﴾
The month of Ramadhan [is that] in which was revealed the Qur'an, a guidance for the people and clear proofs of guidance and criterion. So whoever sights [the new moon of] the month, let him fast it; and whoever is ill or on a journey - then an equal number of other days. Allah intends for you ease and does not intend for you hardship and [wants] for you to complete the period and to glorify Allah for that [to] which He has guided you; and perhaps you will be grateful.
The concession for the sick comes from Allah's wish for ease.
Where the ruling is recorded
- al-Hidaya, Kitab al-Sawm, chapter on what requires qada and kaffarah, section on those excused. A sick person who fears the illness will increase may leave the fast and make it up.
- Radd al-Muhtar (Ibn Abidin), Kitab al-Sawm, section on the excuses that permit not fasting. Harm is known by clear signs, experience, or the report of a competent Muslim doctor who is not openly sinful.
- al-Mughni (Ibn Qudama), Kitab al-Siyam. Agreement that illness which fasting worsens permits not fasting.
This answer is pending review by the scholars on our team. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.