Is it permissible for a diabetic to use insulin if it is manufactured from pigs, cattle, or humans, bearing in mind that seeking treatment with unlawful substances is forbidden?

If it is confirmed that injections contain extracts from pigs, or animals that were not slaughtered Islamically, or carrion, or humans, then it is impermissible to use them for treatment except in cases of extreme necessity and when no alternative is available. This is because the general rule is that it is forbidden to treat with impure substances, and Allah has permitted forbidden things in times of necessity. The composition of the medicine can be ascertained by asking experts.