Although treatment of OCD symptoms with serotonin reuptake inhibitors (SSRIs) such as Prozac (Fluoxetine), Zoloft (Sertraline) and Paxil (Paroxetine), or the tricyclic antidepressant Anafranil (Clomipramine), can be effective, not everyone responds to these medications. Predicting whether or not you will respond to an OCD medication involves looking at a few factors.
Age of Onset - Although there is not universal agreement, there are a number of studies that suggest that age of onset (when the symptoms started) predicts whether you will respond to drug therapy. Specifically, the later in life your symptoms appear, the better the chance you have of responding to medication.
Duration of Illness - The less time you have been experiencing symptoms of OCD, the better the chance that you will respond to medication. Those with symptoms that have lasted for years or decades may have what is referred to as treatment resistant OCD.
Symptom Severity - If your symptoms are mild to moderate, you are likely to have a better response to medication than those whose symptoms are severe. Severe symptoms are often associated with more complicated cases involving depression as well as personality and psychosocial difficulties that can make treatment more challenging.
Nature of Symptoms - Compulsive hoarding and obsessions with bodily themes do not seem to respond well to treatment with medication. In these cases, psychotherapeutic techniques may be more effective.
Insight - The more you are able to recognize that your fears are unfounded, exaggerated or irrational, the more likely you are to respond to treatment with medication.
Personality Disorders - Having a personality disorder such as obsessive compulsive personality disorder or schizotypal personality disorder makes it less likely that you will benefit from medication.
Sources:
Erzegovesi, S., Cavallini, M.C., Cavedini, P., Diaferia, G., Locatelli, & Bellodi, L. "Clinical predictors of drug response in obsessive-compulsive disorder" Journal of Clinical Psychopharmacology 2001 21: 488-492.
Tukel, R., Bozkurt, O., Polat, S., Genc, A., & Atli, H. "Clinical predictors of response to pharmacotherapy with selective serotonin reuptake inhibitors in obsessive-compulsive disorder" Psychiatry and Clinical Neurosciences 2006 60: 404-409.
