Normally, prior to the testing of new substances on humans, they are tested on animals.
The reason for this is to see whether there are any adverse effects.
There is international legislation in place that requires this to be the case, but it remains to be seen whether the entire world will follow this.
The area has been a point of controversy for almost two centuries, with the animal rights movement starting in the United Kingdom.
Safety of subsequent human subjects and users. Gains in field of veterinary medicine. Benefits to medicine.
Harm to other beings for our benefit. Possible infringement of rights.