[Q]: What is the ruling on a fasting person getting injected with a needle in his vein or his muscle and what is the difference between the two?

[A]: That which is most correct is that they do not break one’s fast, however injecting oneself with a needle from which nutrition is gained does break the fast. Likewise, one’s fast is not broken due to a blood test because it is not like ḥijāmah (cupping). The most correct position of the scholars is that ḥijāmah breaks the fasts of both the doer and the one it is being done to according to the statement of the Prophet (صلى الله عليه وسلم):

Both the ḥājim [the one who is doing the cupping] and the maḥjūm’s [the one who cupping is being done to] have broken their fasts. [Collected by Abū Dāwūd and Tirmidhī, graded ṣaḥīḥ by al-Albānī]

Source: تحفة الإخوان بأجوبة مهمة تتعلق بأركان الإسلام. ص.١٤٠
Translated by: Munīb al-Ṣumālī