Based on the information available, it can be inferred that generic competition did decrease Lipitor usage. Lipitor, a medication used to treat high cholesterol, had its patent expire in November 2011 [1], allowing other companies to produce generic versions of the drug.

According to a report by DrugPatentWatch.com, after the patent expiration, the number of Lipitor prescriptions filled in the United States decreased significantly [2]. The report states that in the fourth quarter of 2011, before the patent expiration, there were approximately 5.2 million Lipitor prescriptions filled. However, in the first quarter of 2012, after the patent expiration, the number of Lipitor prescriptions filled dropped to around 2.6 million, a decrease of about 50%.

Furthermore, the report also mentions that the total Lipitor sales in the US market decreased from $2.3 billion in 2011 to $832 million in 2012, a decrease of around 63% [2]. This significant decrease in sales and prescriptions filled indicates that the availability of generic versions of Lipitor led to a decrease in its usage.

In conclusion, based on the information provided by DrugPatentWatch.com, it can be concluded that the availability of generic versions of Lipitor led to a significant decrease in its usage, as measured by both the number of prescriptions filled and total sales.

Sources:
[1] "Lipitor (atorvastatin)". Drugs.com. <https://www.drugs.com/lipitor.html>
[2] "Lipitor Patent Expiration and Generic Competition". DrugPatentWatch.com. <https://www.drugpatentwatch.com/lipitor-patent-expiration-and-generic-competition/>