Then came the Hippies and "free love."
When I worked at California School for the Deaf in the late '60s and early '70s quite a few of the students were known or suspected to have become deaf as a result of prenatal drug damage. The rubella epidemic that happened at the same time also caused prenatal damage, and sometimes women used illegal drugs and had rubella during the same pregnancy.
The kids who were born deaf as a result of the drugs and/or disease usually also had other neurological damage, such as learning disabilities, ADHD, autism, etc. and there were probably lots of other children in that generation who could hear, but had prenatal damage to their brains.
Now we have vaccine to prevent Rubella, but illegal drugs still abound. People are unlikely to remember to use birth control when they're high, so babies with resulting neurological damage are sometimes born today.
Of course there have always been some babies with prenatal damage, and I certainly don't want to imply that drug use is necessarily a factor. Also, a lot of conditions are diagnosed now that weren't recognized before. But the high number of people with those conditions is one of the many problems illegal drugs cause in our society.