Prenatal Drug Exposure

Hello! My fiancé and I are considering adopting my nephew who is currently 5 months old. He was born addicted to heroin, meth, and also had Xanax and benzos in his system. My aunt, the mother, is still using drugs. Therefore, my other aunt who is older considered adopting but is not able to. My fiancé and I have been talking about having our own for a while, and when I heard about my nephew being born like this i just felt something pulling me towards adopting him. My question is, does anyone know or have experience with children born addicted to these drugs? He did have withdrawals at birth but they got it all out and now at 5 months, appears normal. His foster family says that you would never know anything happened aside from the fact that he has night terrors like clockwork. Any suggestions? I am researching professional sources as well.