Lipitor is a brand name for atorvastatin, which is a medication used to lower cholesterol levels. According to the first source , Lipitor's primary function is to inhibit the enzyme HMG-CoA reductase, which is responsible for cholesterol synthesis. It is important to note that the source does not mention any direct link between Lipitor and antidepressants.
The second source  is a research article that explores the effects of atorvastatin on depression in patients with coronary heart disease. The study found that atorvastatin did not significantly affect depressive symptoms in patients, suggesting that it does not decrease antidepressant effectiveness. However, it is important to note that this study focused on atorvastatin's effects on depression in patients with coronary heart disease, not on its potential interactions with antidepressants.
The third source  discusses ginkgo, an herbal supplement that is sometimes used to treat depression. The source notes that ginkgo may interact with certain medications, including antidepressants, and may increase the risk of serotonin syndrome, a potentially life-threatening condition. However, this source does not mention any potential interactions between Lipitor and antidepressants.
In summary, while there is no direct evidence suggesting that Lipitor decreases antidepressant effectiveness, it is important to speak with a healthcare provider before taking any new medications or supplements, including Lipitor and ginkgo, especially if you are currently taking antidepressants. Healthcare providers can provide personalized advice and guidance on potential interactions and risks based on individual health factors and medication regimens.