Thank you for the opportunity to help you with your question!
The message in this ad is saying that men won't accept a woman as a friend because she is doing drugs. I think this is effective because it demonstrates that drugs often cause social strife and non acceptance of others. This non acceptance isn't necassarily from men toward women. It can be from either sex against either sex.
Here is the ad that I have found: https://www.google.com/search?q=drug+prevention+ad&biw=1660&bih=937&source=lnms&tbm=isch&sa=X&ved=0CAYQ_AUoAWoVChMIvtTP66rKxwIVAx0-Ch3Bxwr2#imgrc=PTiMHNSk0LG0MM%3A
Please let me know if you need any clarification. I'm always happy to answer your questions.