Clue: Time to stockpile drug before trading price leads to fall in value (10)
Answer: DEPRECIATE
Explanation: Definition: fall in value
An envelope ('to stockpile') of E ('drug') plus PRECI, an anagram ('trading') of 'price' in DATE ('time'). 'Leads to' here is just a link between wordplay and definition, not an indication of the first letters of anything.