14 CFR § 121.803 Emergency medical equipment:

"For treatment of injuries, medical events, or minor accidents that might occur during flight time each airplane must have the following equipment that meets the specifications and requirements of appendix A of this part

I was interested to see that it's not a huge list. Here, for example, is the full list of drugs (some of which are injectable):

Analgesic, non-narcotic, tablets, 325 mg
Antihistamine tablets, 25 mg
Antihistamine injectable, 50 mg, (single dose ampule or equivalent)
Atropine, 0.5 mg, 5 cc (single dose ampule or equivalent)
Aspirin tablets, 325 mg
Bronchodilator, inhaled (metered dose inhaler or equivalent)
Dextrose, 50%/50 cc injectable, (single dose ampule or equivalent)
Epinephrine 1:1000, 1 cc, injectable, (single dose ampule or equivalent)
Epinephrine 1:10,000, 2 cc, injectable, (single dose ampule or equivalent)
Lidocaine, 5 cc, 20 mg/ml, injectable (single dose ampule or equivalent)
Nitroglycerin tablets, 0.4 mg