Many Western medicines that have been effective at first in curing certain diseases have later been found to have harmful side effects, antibiotics being a prime example for many people.
但目前無法解析出有效成分，卻並不表示動物用藥的療效就被全盤否定，或再無發展性。西藥在發現之初，確實對某種疾病有藥到病除之效，卻往往在使用的幾年後被發現有副作用。許多人身受其害的抗生素即是一例。