Baladhur the Memory Drug
Baladhur was widespread from at least the 9th century into Ottoman times, and seems to have had a social profile among the educated classes because of its addictive qualities. In fact, many physicians advised against it altogether because overuse and/or improper preparation could actually lead to dementia and irascibility, the opposite of why people were taking it. Stories abound of scholars who ultimately suffered because of their baladhur use. Richardson focuses on a man named Shihab al-Din al-Hijazi, who early in life was an outstanding student of Islamic Studies, but during his 20's suffered a period of acute mental instability attributed to his years of baladhur use. Even upon his recovery he suffered chronic memory loss, and so had to make his career elsewhere.
The social context for baladhur's popularity leads me to relate it to steroids in modern sports. Put simply, memorization was the key skill scholars possessed in the medieval Islamic world, and the scholarly world was known for its intense competition such that it is unsurprising many sought an edge despite the pitfalls. The use of writing as a memory aid only became accepted during the 9th century. Even during the Mamluk period of the 1300's and 1400's, the prevailing view was that you could only claim as knowledge what was in your head, and scholars were often called upon to recite long books during public performances. In public debates, scholars would have to draw on any number of memorized accounts and traditions, complete with lengthy chains of authorities verifying the information, and errors would open one to ridicule. At stake was a great deal of wealth, for not only would rulers heap financial rewards upon prominent religious scholars, but as Michael Chamberlain has shown, the key to maintaining wealth and influence across generations of political instability was to earn and keep positions in mosques and madrasas that went to the best scholars.
Semecarpus anacardium is still used in India as an herbal remedy.