Physical Effects of Drug Addiction. Physical effects of drug addiction vary by drug but are typically seen in all systems of the body. Some of the primary physical effects of drug addiction take place in the brain. Drug addiction changes the way the brain functions and impacts how the body perceives pleasure. These effects of drug addiction are because the drug repeatedly floods the brain with the chemicals dopamine and serotonin during drug use. The brain adapts and comes to expect, and depend on, these drug-induces highs. Physical effects of drug addiction are also seen in babies of drug abusers as well as in mortality statistics. One effect of drug addiction is: children born to drug-using mothers can be cognitively affected throughout life. Regarding mortality, one-in-four deaths are due to ...