Schizophrenia pipeline shifts from D2 to muscarinic mechanisms

Reading the signal

Antipsychotic therapy has been defined by dopamine D2 receptor antagonism since the introduction of chlorpromazine in 1952. The first-generation antipsychotics, the second-generation atypical antipsychotics, and the partial-agonist class (aripiprazole, brexpiprazole) are all D2-pathway agents with varying receptor profiles around the central D2 mechanism.

The xanomeline-trospium approval in 2024 introduced a non-D2 mechanism into the schizophrenia commercial category. Xanomeline targets muscarinic M1 and M4 receptors; trospium is a peripheral muscarinic antagonist that mitigates peripheral muscarinic side effects. The combination produces antipsychotic effect through a mechanism that does not engage the D2 pathway directly.

The pipeline of muscarinic-targeted programs has expanded substantially:

• Multiple programs targeting M1 and M4 with various selectivity profiles
• Adjacent muscarinic mechanisms targeting different receptor combinations
• Earlier-stage programs exploring muscarinic mechanisms for adjacent indications (Alzheimer's psychosis, bipolar disorder)

The differentiation versus the D2 class is on tolerability (no extrapyramidal side effects, no prolactin elevation), on efficacy in negative and cognitive symptoms (where the D2 class has historically been weaker), and on the metabolic-side-effect profile.

Commercial implications

For sponsors of muscarinic schizophrenia assets and for sponsors of D2-pathway incumbents:

1. The class differentiation conversation is now active in schizophrenia in a way it has not been for decades. The D2 class has been positioned on receptor-binding-profile differentiation; the muscarinic class introduces a step-change differentiation that the D2 class has to respond to
2. The negative-and-cognitive-symptoms efficacy story is a commercial axis that has been under-developed. If muscarinic mechanisms deliver on this dimension, the commercial framing of antipsychotic therapy reshapes
3. The long-acting injectable schizophrenia commercial category, where adherence is the principal commercial driver, will be reshaped by the introduction of muscarinic LAI formulations once they emerge

What we are watching

• Pivotal trial readouts for the next-generation muscarinic schizophrenia programs in the next 12 to 24 months
• Real-world uptake curves for xanomeline-trospium and the access frame in major markets
• Long-acting injectable muscarinic formulations as they enter clinical development