Is oxycodone making you gain weight?

Unfortunately, no. Wikipedia it.

The most commonly reported effects include constipation, fatigue, dizziness, nausea, lightheadedness, headache, dry mouth, anxiety, pruritus, euphoria, and diaphoresis.[66] It has also been claimed to cause dimness in vision due to miOSis. Some patients have also experienced loss of appetite, nervousness, abdominal pain, diarrhea, dyspnea, and hiccups,[16] although these symptoms appear in less than 5% of patients taking oxycodone. Rarely, the drug can cause impotence, enlarged prostate gland, and decreased testosterone secretion.[67] In high doses, overdoses, or in patients not tolerant to opiates, oxycodone can cause shallow breathing, bradycardia, cold, clammy skin, apnea, hypotension, pupil constriction, circulatory collapse, respiratory arrest, and death.[16] There is a high risk of experiencing severe withdrawal symptoms if a patient discontinues oxycodone abruptly. Therefore therapy should be gradually discontinued rather than abruptly discontinued. People who use oxycodone in a hazardous or harmful fashion are at even higher risk of severe withdrawal symptoms as they tend to use higher than prescribed doses. The symptoms of oxycodone withdrawal are the same as for other opiate based painkillers and may include "anxiety, nausea, insomnia, muscle pain, fevers, and other flu like symptoms."[20] Withdrawal symptoms have also been reported in a newborn whose mother had been injecting OxyContin during pregnancy.[68]