First of all will you Marry me. It's great you are trying to help your husband.
Seriously though you are right, the oral steroids are not very good on the liver depending on how you use them and injectible are far safer. Prop alone probably won't be the answer and if this is his first time I recommend he go with Test e instead. That way he would only need 2 shots a week for 12 weeks at 500mg per week or 250mg per shot. He should see some great gains. With prop he will be pinning every day or every other day at least.

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The Fool say in his heart "There is no God"