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OTC drugs have six ways of affecting a prescription medication:
• OTC drugs can act additively or synergistically when administered with other drugs.
• OTC drugs can enhance or diminish the absorption of another drug from the gastrointestinal tract.
• OTC drugs can alter the distribution of other drugs.
• OTC drugs can alter the renal excretion or effectiveness of another drug.
• OTC drugs can interfere with or affect the desired effect of another drug.
• OTC drugs can decrease the biotransformation of another drug resulting in increased toxicity.