"If there is anyone with old injuries at home, let them take the healing pill first before taking the marrow cleansing pill. It will help condition their bodies and heal any hidden injuries that have lingered even for years. I am sure that grandpa Li has a lot of those, so he must take a healing pill first.
Also, before you take the marrow cleansing pill, you have to prepare yourself mentally. It is painful. You are going to feel as if someone is grinding your bones and cutting your flesh a full hour.
If you can endure it to the end, it will remove the impurities in your body and make your body optimal for cultivation. Again, an advantage for future cultivation.
If you can't endure, then you will also have to limit your cultivation. With impurities in the body, the rate at which you can absorb spiritual energy is limited and breakthroughs are going to be challenging. So, I would advise enduring the pain for that one hour.
