Hamilton told MLB.com this week that he's sick with sinus congestion that makes him prone to dizziness and sensitive to the lights at major league stadiums.
Hamilton's drug use led to multiple suspensions from 2003 to 2006, before he made his major league debut.
"You have a hallway up the middle of your nose and sinus cavities on each side," Hamilton told the Times. "When you breathe air, it goes up and down the hallway.
"Same thing when you do drugs, it goes up the hallway, not into the sinus cavities. I told the doctor I had never had allergies before I started doing any of that stuff, but he said [drug use] has nothing to do with it."
Hamilton, who entered Thursday's game hitting just .214, has scheduled a visit with an allergist after suffering from sinus and throat discomfort.
"You think about the consequences of the decisions you made, especially when you put things in your body that aren't good for you," Hamilton told the newspaper. "But your body is a fascinating thing. It can heal itself. From the doctors I've talked to, it seems like the effects from the years of drug use have healed up."