There was a woman last year who posted on mumsnet, absolutely terrified because her son had grown at a very fast rate, and at 2 was the size of a 4 year old and had started growing pubic hair. Doctor's realised that the kid had been accidentally absorbing testosterone from his father. The father was using a prescribed T gel and it was still present on his hands when he picked up his son.

Doctor's couldn't say for sure whether or not the child would suffer long term health issues as a result. The parents started a campaign, to issue new guidance for T gel users and so that patches/tablets could be considered for parents, rather than gel, which was potentially transferable.

But sure, take really high testosterone medication and then breastfeed your baby. Nothing bad can happen.