There are no significant known side effects to this form of contraception, apart from the elephants’ avoiding the vehicle from which it is administered in some cases!
Before immunocontraception was developed, researchers attempted to use medicine that had a steroidal base or one of sex hormones. However, the increased hormones caused the males to harass the females without let up. This, in turn, forced the cows away from the herd and their young in an attempt to escape the males.
One of the few suspected negative implications lie in the fact that elephants are, by nature, social animals that value families. Inhibiting their abilities to procreate may have some long-term effect on the social structure, roles and responsibilities within the herd. Cost implications may have a bearing on some of the less financially well off parks and reserves.
While this is not a solution to existing over populations of elephants, it is a prevention against reaching such a situation in the future. This carries important advantages – both environmentally and financially.