Why Antidepressants Are Used for IBS

You might be wondering why your doctor would prescribe an antidepressant for your irritable bowel syndrome (IBS) if you are not depressed. Or, perhaps like many IBS sufferers, you do suffer from depression or anxiety alongside your IBS, so the idea makes a little more sense, but you are curious as to what effects an antidepressant might have on your IBS symptoms.

The following overview will answer the question of why antidepressants are sometimes used as a treatment for IBS and educate you as to the types of antidepressants that are commonly prescribed to IBS patients.

Why Antidepressants Are Used for IBS

Although medications in this class are labeled as antidepressants, they have effects that go beyond stabilizing a depressed mood. Antidepressants have been shown to reduce anxiety and pain sensations while having positive effects on the digestive system.

Physicians may prescribe an antidepressant to an IBS patient, but this is considered an "off-label" use of the drug, as no antidepressant has received FDA approval as an IBS treatment. However, the American College of Gastroenterology, after an extensive research review, concluded that there is enough research support on the effectiveness of two classes of drugs--TCAs and SSRIs--to recommend their use in treating IBS.

Specifically, antidepressants have been found to have a positive effect on gut motility and visceral hypersensitivity. It has been hypothesized that the beneficial effects of antidepressants on IBS symptoms are a result of the action of these medications on the neurotransmitters found in the brain and the gut.

Types of Antidepressants Used in IBS Treatment

Antidepressants used for IBS generally fall into one of the following classes:

Tricyclic Antidepressants (TCAs)

Tricyclic antidepressants are the elder statesmen of the antidepressants. It has been well-documented that tricyclic antidepressants have anti-pain and gut-slowing qualities, and seem to do this by acting on the neurotransmitters serotonin and norepinephrine. This slowing down of gut motility makes the TCAs better suited for the treatment of diarrhea-predominant IBS (IBS-D).

Unfortunately, the same action (anticholinergic effect) that results in slowing down the intestinal tract can occasionally lead to side effects, including drowsiness, dry mouth, blurred vision, sexual problems, dizziness, tremors, headache and weight gain. TCAs are generally prescribed at lower doses when treating IBS than when used to treat depression. The following are examples of TCAs that might be prescribed for IBS:

Elavil (amitriptyline)
Tofranil (imipramine)
Norpramin (desipramine)
Aventyl, Pamelor, Allegron (nortriptyline)

Selective Serotonin Reuptake Inhibitors (SSRIs)

Selective serotonin reuptake inhibitors (SSRIs) are medications that were designed to increase the level of the neurotransmitter serotonin in the nervous system, so as to facilitate a beneficial effect on mood.

Because only the neurotransmitter serotonin is targeted, SSRIs generally have fewer side effects than the tricyclic antidepressants. Common side effects of nausea, diarrhea, anxiety, and headache often lessen as the body adjusts to the medication. The lack of a constipating effect makes the SSRIs a better choice for those who suffer from constipation predominant IBS (IBS-C).

SSRIs may also result in prolonged side effects of sexual difficulties (loss of sex drive and/or difficulty achieving orgasm) and weight gain. It is important to remember that different people react differently and a person may tolerate one type of SSRI better than another.

The following are some examples of commonly prescribed SSRIs:

Celexa (citalopram)
Lexapro (escitalopram oxalate)
Prozac (fluoxetine)
Paxil (paroxetine)
Zoloft (sertraline)

5-HT3 for Depression

Researchers have looked at medications that target specific serotonin receptor sites known as 5-HT3 receptors. The controversial Lotronex falls into this category.

Due to the risk of serious side effects, the FDA has imposed strict limits on the prescription of Lotronex. There is one 5-HT3 antidepressant, Remeron (mirtazapine). Data is limited as to the effectiveness of Remeron for IBS and therefore may be less commonly prescribed to IBS patients.

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_{Lacy, B., Weiser, K. & Lee, R. "The treatment of irritable bowel syndrome" Therapeutic Advances in Gastroenterology 2009 2:221-238.}

_{Sainsbury, A. & Ford, A. "Treatment of Irritable Bowel Syndrome: Beyond Fiber and Antispasmodic Agents" Therapeutic Advances in Gastroenterology 2011 4:115-127.}