There is a difference of opinion amongst scholars regarding this issue. To get a more precise answer, you will have to specify your marja’. Nevertheless, we will list the opinions of different marja’s below:

Ayatullahs Bahjat, Imam Khomeini and Khamenei: If an injection is nutritional or a tonic (taken for strengthening the body), as an obligatory precaution, one must refrain from taking it, but if it is for medicinal or anesthetizing purposes, it is okay.

Ayatullah Fazel: Nutritional or tonic injections are impermissible (break the fast), but medicinal or anesthetizing ones are permissible.

Ayatullah Makarem: Nutritional, tonic and medicinal are problematic as an obligatory precaution, but anesthetizing ones are permissible.

Ayatullahs Tabrizi, Sistani, Safi, Nouri and Vahid: No injections break the fast whether they are tonics and for nutritional purposes, or for medicinal purposes and the like.[1]

Ayatullah Hadavi Tehrani has replied to this inquiry in such:

Taking injections aren't considered eating or drinking and don’t break the fast (making taking them permissible), although it is better to refrain from nutritional injections and ones that are tonics.

For further information, see:

1- Fasting and drug consumption, Question 2986 (website: 3479).

2- Using sprays while fasting, Question 5845 (website: 6063).