How Long Before I Can Sleep on my Stomach

After 6 weeks I would suggest it is safe to sleep on your stomach.Give it a try and it will be uncomfortable, but unlikely to be harmful. Remember trying to touch your toes can be uncomfortable , but not harmful, just be sensible

Jeremy Hunt

It's really not proper for plastic surgeons in this forum to issue postoperative instructions. This needs to be defined by your plastic surgeon.

Congratulations on having undergone the breast reduction procedure;  this operation tends to be one of the most patient pleasing operations we perform. Your plastic surgeon will be your best resource when it comes to returning to specific activities; you may be surprised as to how recommendations may vary depending on specific plastic surgeon preference. In my practice, assuming the use of a supportive bra, I asked my patience to wait approximately 3 months before lying on their chests after any type of breast surgery.

 Best wishes.

This is certainly a question that you should ask your surgeon.  If you are healing well and there are no other issues 6 weeks should be fine.