Obsessive-compulsive disorder is one of the few major psychiatric conditions where the pharmacology has barely moved in a generation. First-line treatment is still a serotonin reuptake inhibitor or clomipramine, a tricyclic from the 1960s, and for the large share of patients who do not respond adequately, the options thin out quickly: augmentation with an antipsychotic, and at the severe, refractory end, deep brain stimulation under a humanitarian device exemption. No genuinely new first-line mechanism has arrived in decades. Against that stagnant backdrop, a cluster of academic trials is now testing a different approach, repurposing existing drugs whose mechanisms sit outside the serotonin model, and it is worth being precise about what kind of development this is.
The stalled baseline
The serotonin hypothesis has defined OCD pharmacology since the field discovered that serotonergic drugs help and most others do not. SSRIs and clomipramine remain the evidence base, roughly 40 to 60 percent of patients get insufficient relief from them, and the established next step is to augment with an antipsychotic such as risperidone or aripiprazole. Beyond that, glutamate-modulating agents have been explored with mixed and largely disappointing results, and deep brain stimulation exists for the small population of severe, treatment-refractory cases. The throughline is that OCD has been pharmacologically underserved relative to depression or schizophrenia, and that the absence of a new mechanism is not for lack of need.
The cluster
The new signal is a concentration of academic activity, led notably by the University of Chicago group under Jon Grant, testing repurposed drugs in OCD. Two trials are instructive precisely because they pull in opposite pharmacological directions.
The first is tolcapone, a catechol-O-methyltransferase inhibitor used as an add-on in Parkinson’s disease. A pilot crossover trial of 20 patients found that two weeks of tolcapone produced a significant improvement in OCD symptoms over placebo, a 16.4 percent reduction in the standard symptom scale against 3.6 percent for placebo, and a larger double-blind trial followed, funded by a disease research foundation. The rationale is mechanistic: as the only brain-penetrant COMT inhibitor, tolcapone raises prefrontal dopamine, which is hypothesized to improve the cognitive control and flexibility that OCD impairs. It reframes the disorder as partly a cognitive-control deficit rather than a purely serotonergic one.
The second is valbenazine, a VMAT2 inhibitor approved for tardive dyskinesia, now in a randomized double-blind placebo-controlled crossover trial in moderate-to-severe OCD. VMAT2 inhibition reduces synaptic dopamine, the opposite of what tolcapone does. That two trials at the same center are testing drugs that move dopamine in opposite directions is the most honest indicator of where the field actually is: the dopamine story in OCD is unsettled enough that both raising and lowering it are live hypotheses. Neurophysiology and mechanistic work at other academic centers rounds out a broader uptick in attention to a disorder that had gone quiet.
The distinction that matters
It would be easy to read this as an emerging OCD pipeline, and it is important not to. This is a research-interest revival, not a commercial development program, and the difference runs through everything about it.
The candidates are repurposed drugs that are off-patent or already approved for other uses. Tolcapone is generic. Valbenazine’s OCD work is investigator-initiated rather than a manufacturer’s program. There is little composition-of-matter upside in either, which is exactly why pharmaceutical companies are not driving this and academic groups and disease foundations are. The trials are small, proof-of-concept crossovers appropriate for generating a repurposing signal and far from anything resembling registration. And the underlying economics are the reason the field stalled in the first place: OCD is a smaller market than depression, novel-molecule development is expensive and risky, and the commercial incentive to pursue it has been weak. Repurposing is the path available precisely because it is cheap and fundable outside the commercial system.
For an investor or corporate-development reader, the takeaway is therefore not that a near-term OCD opportunity is forming. It is that the science is moving again in a neglected indication, mostly outside the industry, which is a genuine and underwatched signal of a different kind.
The caveats
Several cautions apply at once. Repurposing pilot signals frequently fail to replicate at larger scale, and a significant result in a 20-patient crossover is a starting point, not proof of anything. Tolcapone carries a boxed warning for fatal liver toxicity and requires hepatic monitoring, a serious constraint for chronic use in a chronic disorder, so even a clean efficacy result would leave a real-world tolerability problem. The opposite-direction dopamine bets mean that at most one of the mechanistic stories can be correct, and possibly neither. And the framing of a coordinated academic push overstates it: these are independent groups with convergent interest, and the convergence reflects shared frustration with the serotonin ceiling and the availability of repurposable mechanisms, not a strategy anyone is running.
The frame
The OCD cluster is, in a sense, the mirror image of the ketamine story the desk has covered. Ketamine is an off-patent molecule being pushed into every available indication by commercial reformulation. OCD is a single indication being approached by repurposing off-patent molecules, but driven by academia because the commercial incentives are not there. Both are off-patent-molecule stories. One is propelled by the market, the other proceeds in spite of its absence. That is what makes the OCD cluster worth covering: it is a place where the science is restarting without the industry, which is a less visible and less common signal than a new commercial program.
After decades of stagnation, the mechanistic conversation in OCD has resumed, on hypotheses about dopamine and cognitive control rather than serotonin alone. Whether any of these repurposed candidates survives a larger trial is unknown, and the base rate for repurposing signals is humbling. The more interesting question sits one step beyond the data: if something does work, whether the commercial system shows up to develop it, or whether OCD remains an indication that academia explores and industry continues to skip.