Ritalin basically is an amphetamine. Such drugs used chronically can put stress on the heart, affect the brain, metabolism, cause weight loss, and other problems. The other very serious problem is the fact that he is injecting them. This can lead to infection with HIV, hepatitis C, and some other infections if he is sharing needles or using dirty needles. He could develop an infection in the blood (sepsis), which can spread and cause damage to heart valves, the bones, or whatever organ it may spread to. You mention he has a history of opiate abuse, and that he has been clean of opiates, but he still has an addiction and does need help. He has simply substituted the opiates with another drug. If he doesn t want professional treatment with a doctor or treatment center, he might consider going to a self-help group such as Narcotics Anonymous (NA). NA deals with the disease of addiction and not any one particular drug, so this might be acceptable for him to check out. Hope this helps.