Buying Oxycodone 30 mg online without a prescription is illegal and dangerous. Always consult a healthcare professional and obtain a valid prescription before Purchasing Oxycodone Online. Oxycodone is a prescription opioid medication used to treat moderate to severe pain and alters how the brain and nervous system respond to pain. A 30 mg dosage of oxycodone is considered relatively high and is usually prescribed for individuals who require stronger pain relief.