Cymbalta, the blockbuster successor to Prozac, has developed a reputation for leaving patients with painful and debilitating withdrawal symptoms.

Cymbalta is one of a class of antidepressant drugs called selective serotonin and norepinephrine reuptake inhibitors, or SSNRIs. According to manufacturer Eli Lilly’s website, the actual mechanism by which Cymbalta works is not known.

Scientists believe Cymbalta may work by increasing the activity of the neurotransmitters serotonin and norepinephrine, thereby both improving negative mood and reducing the perception of pain.

The FDA first approved Cymbalta as a treatment for depression in August 2004. Since then it has received additional approval as a treatment for neuropathic pain associated with diabetes, generalized anxiety disorder, fibromyalgia, and chronic musculoskeletal pain such as that associated with osteoarthritis and low back pain. Eli Lilly is currently campaigning to have Cymbalta approved as a treatment for chronic fatigue syndrome.

Eli Lilly developed Cymbalta to fill a gap in antidepressant sales left when the patent for Prozac expired in 2001. As a product, Cymbalta has been a resounding success. From its introduction in 2004 to the expiration of its patent in 2013, Cymbalta earned a total of $24 billion in sales. Sales dropped significantly after that patent expiration, when generic versions of Cymbalta hit the market.

Cymbalta Withdrawal Symptoms

One allegedly significant drawback of Cymbalta is that ceasing treatment can result in a spectrum of withdrawal symptoms, sometimes referred to as antidepressant discontinuation syndrome. The most dramatic of these symptoms are colloquially known as “brain zaps” — which reportedly feels like electric shocks happening inside the head, sometimes accompanied by nausea, headaches or cognitive effects. Other patients reported symptoms of the body shaking and tunnel vision.

Some Cymbalta patients have continued using the drug solely to avoid the symptoms of Cymbalta withdrawal. Those who managed to wean themselves off the drug have reported having to take several months to do so, and some of them also reported continuation of withdrawal symptoms for several months after completely discontinuing Cymbalta.

The FDA now warns that in clinical trials, discontinuing Cymbalta was followed by withdrawal symptoms in at least one percent of patients. Symptoms observed included dizziness, headache, nausea, diarrhea, paresthesia, irritability, vomiting, insomnia, anxiety, hyperhidrosis and fatigue.

The labeling for Cymbalta has included a list of these withdrawal symptoms, with some variation, since 2004. However, a recent Cymbalta class action lawsuit alleged this labeling is misleading, based on studies commissioned by Eli Lilly itself that found withdrawal symptoms in as many as 51 percent of patients.

Eli Lilly’s marketing for Cymbalta has a history of receiving negative attention. The FDA has sent the company several warnings from 2005 through 2010 about various improper practices in its Cymbalta marketing. In light of that history and of Cymbalta’s tendency to be habit-forming, Eli Lilly’s most recent Cymbalta marketing could understandably raise eyebrows.

The “Cymbalta Promise” campaign offers new patients a free supply of Cymbalta for 60 days – which was, according to studies commissioned by Eli Lilly, the amount of time it took for about half of the patients in the study to develop withdrawal symptoms.