Doctor Explains Retinol Side Effects. Source: Anything that produces a biological or therapeutic effect in the body also carries the potential for side effects, because the same mechanisms that create desired outcomes can influence other systems unintentionally. Medications, supplements, and even natural remedies work by interacting with cells, receptors, or biochemical pathways — and these pathways are rarely limited to a single, isolated function. For example, a drug designed to lower blood pr