8. The patient has been taking a stable dose of a medication with pain prevention potential for at least 6 weeks prior to the screening visit and agrees to not start, stop, or change dosage of any medication with pain prevention potential during the study period. (E.g., tricyclic antidepressants, anticonvulsants, selective serotonin re-uptake inhibitors (SSRIs), serotonin-norepinephrine re-uptake inhibitors (SNRIs), herbal preparations (e.g. feverfew or St. john's wort)). Botulinum toxin injections and steroid injections to the spine must be discontinued six months prior to Visit 1.