Drug Side Effects Explained

Author: Jim Morelli, MS, RPh
Medical Editor: Louise Chang, MD

• Drug Side Effects: Types
• Drug Side Effects: The FDA's Role
• Drug Side Effects: Surprising Results

It doesn't matter whether we're talking about aspirin or the most sophisticated pharmaceutical on the market, all drugs come with side effects. Many are minor, some are just an inconvenience, a few are serious, and some are just plain strange.

Perhaps the most common set of side effects for drugs taken internally involves the gastrointestinal system. Nearly any drug can cause nausea or an upset stomach, though it may only happen to a handful of users. For drugs used externally, skin irritation is a common complaint.

Drug Side Effects: Types

Side effects fall into several categories. Allergic reactions can happen with any drug and can range from itching and rash all the way up to a life-threatening anaphylactic reaction.

Other side effects simply “come with the territory.” Some drugs can't help but trigger side effects because of their chemical structure. One example is the common allergy drug diphenhydramine (also known by the brand name Benadryl). Though it eases allergy symptoms, it also suppresses the activity of the body chemical acetylcholine, and that leads to drowsiness and a host of other side effects, including dry mouth.

Some drugs have barely noticeable side effects when dosed properly. For example, Warfarin (Jantoven, Coumadin) used to prevent blood clots, is usually well tolerated, but serious internal bleeding can occur.

Side effects may only pop up when certain drugs are mixed with certain other things. These might also be considered drug interactions. Drinking alcohol with narcotic painkillers can lead to trouble breathing. Drinking grapefruit juice can affect the blood levels of several drugs, including the heart drug digoxin.

To find more about a drug's side effects, information about them is available on the label of over-the-counter drug products and on package inserts or printed materials dispensed with prescription drugs. You can also talk to your pharmacist or doctor if you have any questions regarding a drug's side effects.