ok what pain medication does not have nasty side effects?
Pharmaceutical grade opiates IN AND OF ITSELF is actually very gentle on your body, and has a relatively low half life. The biggest problem is usually constipation, as the opiate numbs the digestive system. This is easily remedied with some senna.
Acetaminophen is much harder on your body, namely the liver, than opiates. But your body will digest and metabolize opiates quite safely, assuming the dosage is not too high. If it is, your respiratory system can slow down.
The nastiest side effect would be the possible addiction. Not many people know this, but those who are in true chronic pain are less likely to get addicted. Those who are relatively healthy and abuse these drugs and get high because their dopamine and seratonin levels are normal. When they take opiates recreationally, their dopamine and seratonin levels get jacked up, hence the word "high".
If you are in true chronic pain, your dopamine and seratonin levels are very low as a result. Taking opiates might return them to normal levels, and thus they are not as likely to get high and addicted.