If you are taking sleeping pills or narcotics, stay away from antihistamines because of the possibility of over-sedation, states the Lifetime Health Letter.

The interaction between prescription and over the counter medicines can cause serious problems for consumers. For example, if you are taking blood pressure drugs, avoid decongestants because they can cause fast pulse and continued high blood pressure.

Pain relievers with diabetes medications may lower blood sugar to a dangerous level. Antacids interfere with several drugs, including tetracycline and ulcer drugs such as Tagamet. If you need an antacid while taking a prescription drug, separate the doses by at least an hour.

For years, we have counted on the pharmacist at the corner drug store to keep a record of all our medicines and be there to answer questions about drug interactions. However, with alternative sources of drugs, it is up to you to inform your health care providers about all prescription and over-the-counter products you are taking.