Diet Pills During Pregnancy?

My mother in law is 72 years old now, but 54 years ago she was a newly wed starting a family. Her first child was a big baby. When she became pregnant with her second child, she begged her doctor to help her have a smaller baby. Her OB/GYN prescribed diet pills and she took those little pills during her entire pregnancy. Her baby girl was huge in spite of those diet pills.

After my sister in law was born, my mother in law said the baby cried constantly. Once they got home from the hospital, my mother law says that my sister in law slept all the time. From birth until age 12, my sister law’s favorite place was her bed. She slept constantly. Even now, at age 51, her favorite pass time is sleeping.

During adolescence and young adult hood, my sister in law became addicted to methamphetamine. She said taking the drug made her feel normal. She is now a recovering drug addict and alcoholic, but she still misses the drugs. Her daughter, my niece, is also a methamphetamine addict. My niece spent two years in prison for criminal activity associated with drug abuse. The cycle continues.

Is there anyway possible the diet pills my mother in law took during her pregnancy 52 years ago could have caused my sister in law’s drug addiction and subsequently my niece’s drug addiction?

I can’t help but wonder. Although I have suggested this possibility to my mother in law, she thinks it is far fetched. She also doesn’t think taking those diet pills while pregnant was wrong — she has justified it as being prescribed by her doctor and she was just following his instruction.

Could there be a connection?