Taking different drugs at the same time By combining drugs at the same time, the drug interaction in the body may cause loss of effectiveness, or on the other hand it may increase its effectiveness resulting in strong side effects. When you use several types of drugs concomitantly, let's consult with a pharmacist or a physician.   What happens when you take drugs together? Drug-drug interaction sometimes can raise the drug effect and can also lower side effect. On the other hand, it can also lower the drug effect and give some other side effect. For example, in case a person with allergic dermatitis taking anti-histamine drugs develops a stomachache and takes a pain reliever, depending on the person they sometimes get very dry mouthed or develops a constipation. This condition develops because there is the same component in both drugs which increases the drug effect. Depending on the situation some drug combination can cause a serious effect.   Inform the pharmacist all the drugs that you take. To avoid any accident of taking a combination of drugs, it is important to consult with an expert. Before you buy a drug, you should always discuss about the drugs you are currently taking (both doctor prescribed and OTC drugs and any other drugs) with the pharmacist. For people who are taking prescribed drugs and the necessity of taking an OTC drug develops, don't decide by yourself, but please consult a pharmacist or a physician.