Question Summary:
According to Shariah, it is permissible to take an intramuscular injection while fasting,

Question Detail:

I am suffering from a chronic illness and therefore I take intramuscular injection from my doctor. My question is will it nullify my fast if I take intramuscular injection?

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh
An intramuscular (also IM or im) injection is the injection of a substance directly into a muscle. 
 
According to Shariah, it is permissible to take an intramuscular injection while fasting, as long as it is not taken directly into the stomach.  
 
And Allah Ta’āla Knows Best
 
Ismail Desai,
Darul Iftaa
 
Checked and Approved,
Mufti Ebrahim Desai.
 
 
 https://en.wikipedia.org/wiki/Intramuscular_injection, last accessed on 14/11/2015.
 
2 وفي الجائفة والآمة إذا داواهما بدواء يابس لا يفسد صومه وإذا داواهما بدواء رطب يفسد صومه عند أبي حنيفة خلافا لهما وأكثر المشايخ اعتبر الوصول إلى الجوف
(المحيط البرهاني، كتاب الصوم، الفصل الرابع: 3/348؛ إدارة)
 
(جديد فقهي مسائل، عبادات، روزه: 1/179-182؛ نعيميه)