OCD: Pharmacotherapy

Text adapted from "The patient with obsessive compulsive disorder" in Psychiatry in primary care by Peggy A. Richter and Steven Selchen  (CAMH, 2019). 

There is good Level 1 evidence for all of the SSRIs in OCD (citalopram is off-label for OCD in Canada, although it is indicated in the United States and Europe). The tricyclic antidepressant clomipramine similarly has Level 1 evidence for efficacy, and historically has often been considered the most effective pharmacotherapy option, but it is relegated to second–line status because it has a more challenging side-effect profile. All of these medications have the advantage of working on the common comorbid mood and anxiety disorders.

There are two major differences in how these medications are used to treat OCD versus depression:

• Dosing is generally most effective at the upper end of the tested dose range for OCD, which can be higher than the dose range tested for depression.
• There is a longer therapeutic lag before benefits are seen in OCD—generally six to 10 weeks compared with two to four weeks for depression.

It is generally best to discuss the target dose with the patient, stressing that the patient should aim for the upper end of the dose range or until significant side-effects occur, after which it is important to allow at least six to 10 more weeks to assess response. For this reason, drug trials in OCD typically require 12 weeks or more (Fineberg et al., 2015) (see Table 2 for medications and dose ranges).

Although the recommended dose range for citalopram and escitalopram exceeds the Health Canada warnings due to risk of QTc prolongation on ECG, this effect usually is modest and can be managed easily with serial ECG monitoring, ensuring that patients do not exceed the recommended safety thresholds.

Keep in mind that response to pharmacological treatments can differ significantly between OCD and the obsessive-compulsive–related disorders.

Only 40 to 60 percent of patients respond to the first SSRI, so many patients need to try at least a second one. There is clear evidence that  clonazepam and bupropion (Wellbutrin) do not work in OCD, so avoid them for this indication. If a second SSRI fails, most guidelines recommend moving to a second-line option, such as clomipramine or venlafaxine.

Another frequent recommendation is to augment with atypical antipsychotics. Although there is Level 1 evidence for this strategy, a randomized controlled trial of SSRI partial-responders found CBT to be far more effective than an atypical antipsychotic, raising uncertainty about this augmentation approach (Simpson et al., 2013).

Typically, treatment continues for at least one year because there is a high risk of relapse if medication is discontinued early. Most experts recommend referral for CBT to reduce relapse risk. For patients with very severe illness or if a number of medications have been ineffective, long-term continuation of an effective medication is often recommended to maintain stability.

Starting pharmacotherapy for OCD

• Clarify expectations at the start:
  • High doses work best.
  • Increase regularly to the highest dose comfortably tolerated or to the target dose.
  • It takes six to eight weeks to see benefits. Allow 12 weeks for each medication to accurately assess response.
• Start at the usual dose, then increase every five to seven days:
  • escitalopram: 10 mg → 20 mg
  • sertraline: 50 mg → 100 mg → 150 mg → 200 mg
  • paroxetine/fluoxetine/citalopram: 20 mg → 40 mg → 60/80/80 mg
• Allow 10 weeks at the maximum dosage, for a 12-week total on the medication.
• Monitor for change:
  • Use the self-report Yale-Brown Obsessive-Compulsive Scale and monitor two or three behavioural targets.

In OCD: 

• The Role of the Primary Practitioner
• Screening & Assessment
• Diagnosis
• Treatment
  • Pharmacotherapy
  • Psychotherapy
• Resources 
• References