Gelatin, as I can verify from the sources, is not always derived from pig, or animals that the Muslims are not allowed to consume; it may or may not be derived from such animals, and, as such, it cannot be considered as plainly haraam (unlawful). Since there is a possibility of it being derived from pigs, it is only doubtful; although we are to avoid the doubtful, it is not absolutely forbidden.

Assuming that it is derived from pigs, and, there is no alternative to it, then Muslims may take it for treatment purposes. Since it has become a common ingredient in so many medications, and, the alternatives are rare, it may be considered as permissible, according to the rules of Islamic jurisprudence; in this case it falls under the category of those that are permissible under the principle of what is termed in fiqh (Islamic jurisprudence) as ‘umum al-balwa (unavoidable because it is so common).