Depends on how you define “effective” 😉
We know that chlorine is incredibly dangerous if inhaled. It destroys lung tissue, causing people to asphyxiate on their own pulped lungs. It was used as a weapon in World War I, and soldiers were terrified of it. .So why did a US President and a good chunk of Congress get gassed with it as a medical treatment?
That’s like how Marie Curie discovered radium – her note book now is kept in a lead box because it’s that radioactive. We’ve made some great discoveries, but there have been some mistakes to get there.