What are the leading prescription medication drugs being purchased
online world wide?

Dea MTV, 

According to a study published in the Annals of Internal Medicine,
"The most popular drugs sold online are Viagra, Propecia, Prozac,
weight loss pills, birth control pills, and smoking cessation pills. "
(SOURCE: "Drug Sales on the Internet Are Dangerous Experts Say.",
<http://www.chiropracticresearch.org/NEWSinternetdrugsales.htm>).

According to an FDA official: " Lifestyle drugs are very popular,
including Viagra for erectile dysfunction, Propecia for hair loss, and
Xenical for obesity. " (SOURCE:  Jane E. Henney, M.D., E-Regulation
and Public Health, Address Before the 2000 Leonard Davis Institute of
Health Economics University of Pennsylvania Health Policy Seminar
Series (Sept. 29, 2000),
<http://www.fda.gov/oc/speeches/2000/ecommerce.html>). This is
supported by previous researches I made on the subject:

Can a foreign doctor give me a prescription over the internet
<http://answers.google.com/answers/threadview?id=353524> 

Online pharmacy legislation
<http://answers.google.com/answers/threadview?id=249251> 

meds online
<http://answers.google.com/answers/threadview?id=275024>

What are the legal restrictions on offering internet mail order
<http://answers.google.com/answers/threadview?id=234795>

According to a commercial site, 
"Top 10 Most Popular Drugs and Medications Online:
Viagra	
Prozac	
Ultram	
Benadryl	
Zyban	
Ionamin	
Claritin	
Xenical	
Celebrex	
Phentermine" 
(SOURCE: Online Drugs and Medications Information,
<http://www.drugsandmedicationsinfo.com/>). Their methodology or
source of knowledge is not divulged: one could only assumes that it is
based on demand or search for these terms.

I hope this answered your question. Please contact me if you need any
clarification on this answer before you rate it.

Search strategy: "most popular perscription/drugs" online

First time user, definitely will be back... Thanks for the service.