Some OTC drugs require the pharmacist to give extra counselling or special instructions to the person using them. Some OTC drugs are available only through the pharmacist because they contain a restricted ingredient. Keeping some OTC drugs behind the counter also allows the pharmacist to monitor their distribution. Prescriptions aren't needed for OTC drugs because physicians do not need to monitor their use. This is not to suggest that OTC drugs are harmless.
Any drug can be dangerous if misused.
Anyone taking OTC drugs should carefully read the instructions and warnings on the package. Also, the interaction of alcohol with any drug can be dangerous and even fatal. People taking medications should use alcohol with caution or avoid it altogether. Always consult with your doctor or pharmacist if you have to take more than one drug at a time. This precaution will prevent any unpleasant or dangerous drug interactions.