The box insert says the daily dose can be up to 20mg per day for 2-4 weeks. It also states a contradiction for use in patients with renal disease. I think from that we can extrapolate that kidneys can be impacted, and because we are using it at higher doses and for longer periods of time. the impact on kidneys can be greater. The box insert also says it can cause liver and spleen problems, again, at 20mg a day for up to 4 weeks. Using more and for longer most likely increases the possibility of that.
Oxandrolone package insert / prescribing information for healthcare professionals. Includes: indications, dosage, adverse reactions and pharmacology.
www.drugs.com