Enbrel may cause side effects ranging from mild to severe. The following lists include some of the most reported side effects but are not complete. Mild side effects typically subside within a few days or weeks of consistent medication-taking. However, if they persist or worsen you should speak to your doctor. Common side effects: Redness at the injection site Itchy skin Diarrhea Cold-like symptoms Mild fever Infections Serious side effects: Heart failure Extreme fatigue Persistent or worsening fever Bruising Pale skin Worsening symptoms Multiple sclerosis Potentially fatal skin conditions like Stevens-Johnson syndrome (SJS) or toxic epidermal necrolysis (TEN) If you experience any of these serious side effects, you should speak with your doctor as they may be a sign of a serious reaction. Seek immediate medical attention if it is an emergency. In some rare cases, patients can experience allergic reactions. Seek emergency medical care if you experience any of the following symptoms after taking Enbrel. Skin rash Wheezing Tightness in the throat or chest Difficulty talking or breathing Swelling of the face, lips, tongue, or throat