Other causes of unexplained weight loss
could be worms in stool, depression, anorexia
nervosa, AIDS, cancers especially colon cancers, drug abuse, infections and loss of appetite. Loss of appetite can again be due to certain medications, drug abuse, depression, AIDS, acute and chronic infections, cancers and hypothyroidism. Either he does not eat well or there is increased metabolism as in hyperthyroid states, HIV, cancer etc.