Although the SSRIs have major advantages over the TCAs, particularly with respect to safety and tolerability, a medication that has actions not only on serotonin but also on norepinephrine may have some advantages. For example, some authors have suggested that dual reuptake inhibitors may be more likely to lead to remission (Thase et al. 2001). Serotonin–norepinephrine reuptake inhibitors (SNRIs) are dual reuptake inhibitors that affect serotonin and norepinephrine but have little effect on muscarinic, H₁, or ₁-adrenergic receptors. Thus, these medications share many of the tolerability and safety benefits of the SSRIs but add an additional pharmacological action compared with SSRIs—namely, norepinephrine reuptake inhibition. Two SNRIs are currently available in the United States: venlafaxine and duloxetine.