The sudden and substantial decline in the number of fatal overdoses involving the synthetic opioid fentanyl in the USA, in the 12 months July 2023 to June 2024, has generated many hypotheses about causes. Possible causal factors include 1) a diminution in the pool of susceptibles as a result of high fatality rates amongst regular opioid users (2) the effects of harm reduction programs, notably the wide distribution of Narcan and (3) interruptions to the supply as the result of aggressive law enforcement against Mexican producers and traffickers. In the absence of regular and reliable measures of the state of the market, we test the hypothesis that the supply has been reduced by examination of comments on Reddit. Threads on three subreddits r/fentanyl, r/heroin, r/opiates) were examined for the frequency with which market condition related comments indicated shortages in the periods January 2020 to June 2023 and July 2023 to October 2024. For example, in r/fentanyl the term “drought” was hardly used at all in the first period (appearing in 18 of 13,682 threads) but appeared in 143 out of 3,993 threads in the second period. Analysis of terms indicating higher price and lower quality supported this finding. The analysis provides support for the claim that market conditions have tightened in the period July 2023 to late 2024, perhaps contributing to the decline in fatal overdoses.