3 Free radicals must travel to result in local damage. Covalent binding is generally a problem of reactive metabolites. Covalent binding targets include nucleus, ribosomes, and cell wall. A change that occurs in the body due to a drug may not necessarily be toxic, but an adaptation. An underestimated risk is involuntary.
Toxicity requires saturation of metabolic pathways of detoxification.
The brain is susceptible to lipid peroxidation due to its low supply of antioxidants. Too much oxygen is a bad thing. You can be allergic to a product with your first exposure. A free radical produced in the liver is likely to cause damage to cardiovascular tissue. If the danger of the drug is not apparent to the person, they may underestimate the risk of toxicity and take the drug frequently.