In the United States of America, Modafinil is considered a schedule IV drug and requires a prescription. Because of this, purchasing Modafinil in any other capacity is considered illegal, and therefore should be avoided. Modafinil is used to treat daytime sleepiness in individuals who suffer from nighttime obstructive sleep apnea. It is also used to treat narcolepsy.
It is legal to bring Modafinil into the United States unless you have an Rx for it, and even then it is only allowed in the limited amount of 50 pills. Modafinil is only allowed to be marketed for on-label usage by the United States government. Some individuals claim that ADHD can be effectively treated by using Modafinil. However, it is difficult to manage the correct amount to help this disorder rather than hurt it. As such, it is often not prescribed for this usage.
There are no legal methods of purchasing this drug online in the United States without an Rx. As such, there is not much information on where you would be able to purchase it. It has not always been regulated as stringently as it currently is, however there can be severe psychological consequences from using this drug and as such it has been placed under much scrutiny around the world. Many countries actually regulate the use of this drug much more stringently than the United States.
Modafinil is often referred to as a smart drug. This is because it is considered a nootropic, which supposedly heightens the senses and mental functions of the user. This is in a way how it also helps some psychological issues improve, and helps to theoretically help with focus in those suffering from ADHD.
Some athletes use Modafinil as a doping agent, which is truly unethical in the greatest sense. Any drug used as a means to cheat the system and artificially enhance performance against those competing naturally is just terrible sportsmanship.
If you do purchase Modafinil, or have it prescribed to you legally, please use it as directed and safely.