It has terrible withdrawal symptoms.
It should not be withdrawn suddenly. An SSRI (like) withdrawal syndrome can occur. Cymbalta is an SNRI drug, but has very similar withdrawal symptoms. VERY unpleasant.
Eli Lilly, the manufacturer of duloxetine - brand name Cymbalta - warns that "one should not suddenly stop taking this medicine, as this may cause withdrawal symptoms such as dizziness, pins and needles sensations, nausea, difficulty sleeping, intense dreams, headache, tremor, agitation or anxiety. Withdrawal symptoms are temporary and are not the same as addiction." These responses could constitute physical dependence on the drug, but SSRI users do not experience the craving, impulsive use, or long-term relapse risk seen in drug addiction.
During marketing of other SSRIs and SNRIs (serotonin and norepinephrine reuptake inhibitors), there have been spontaneous reports of adverse events occurring upon discontinuation of these drugs, particularly when abrupt, including the following: dysphoric mood, irritability, agitation, aggressiveness, dizziness, sensory disturbances (e.g., paresthesias such as electric shock sensations), anxiety, confusion, headache, lethargy, emotional lability, insomnia, hypomania, tinnitus, and seizures. Although these events are generally self-limiting, some have been reported to be severe.
Patients should be monitored for these symptoms when discontinuing treatment with Cymbalta. A gradual reduction in the dose rather than abrupt cessation is recommended whenever possible. If intolerable symptoms occur following a decrease in the dose or upon discontinuation of treatment, then resuming the previously prescribed dose may be considered. Subsequently, the physician may continue decreasing the dose but at a more gradual rate.
Tapering process may be moot for some patients, and they will still have discontinuation/withdrawal symptoms.
Many patients on the drug longer than the Lilly test trials on discontinuation (which only studied patients after 9 weeks of exposure to cymbalta), report anecdotal evidence of major withdrawals from cymbalta lasting from weeks to many months. Since duloxetine is a newer drug (FDA-approval 2004), not many peer-reviewed articles have been published on its adverse effects or withdrawal phenomena, and effect of long term use is still unknown.