I agree with an animal experiment.

First, It is possible to secure the safety by testing a drug or drugs to be used before human uses.

Second, animals have a human-like organ, therefore the probability of success increase.

Third, nowadays many countries impose the 3R(Reduction·Refinement·Replacement)system, so, that experiment conducts in the way that is not cruel before. 

 Finally, animals do some impossible missions for human. For example In 1957 the dog, which named Laika, board a Soviet Union’s spacecraft. Laika offers many information about occurrence in non-gravity. Like this, animal experiment can be allowed.