​Some of the side effects OxyContin can cause are likely to impair your thinking and reactions. Always be very careful before you get engaged into any activities that require maximum alertness and concentration, as you may not be able to perform after taking OxyContin. Serious side effects of OxyContin are rare but possible in some people, so you will need to make sure you report them to your doctor right away. Serious side effects may mean your treatment is not going as planned, and some changes need to be made to it. The following symptoms are considered serious: seizure, confusion, clammy skin, shallow breathing, slow heartbeat, light-headedness, as well as severe weakness or dizziness. Mild side effects are usually short-lived and tend to disappear on their own without any need for you to worry. Such mild side effects as loss of appetite, headache, dizziness, nausea, dry mouth, constipation, itching, sweating, tired feeling, or vomiting are possible but usually not supposed to cause concern.