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Difamilast (Moizerto) is a selective, PDE4B-preferring topical PDE4 inhibitor and the first PDE4 inhibitor approved in Japan (2021) for atopic dermatitis in patients aged two years and older. Two Phase 3 trials in adults and children showed clear eczema clearance superior to vehicle with a rapid antipruritic effect. Like crisaborole, it is a skin drug with negligible systemic exposure and no CNS or cognition evidence; included here for PDE4-class completeness, not as a nootropic.
- Effective, steroid-free topical for mild-to-moderate atopic dermatitis in adults and children
- PDE4B-preferring selectivity with a rapid antipruritic effect
- Clean safety profile with negligible systemic exposure
- Difamilast preferentially targets the PDE4B subtype, the isoform most tied to inflammatory signaling.
- It was the first PDE4 inhibitor approved for atopic dermatitis in Japan (2021).
- Like crisaborole, it stays in the skin and does not reach the brain; it is on this PDE4 list for class completeness, not as a nootropic.
Mechanism
A selective PDE4 inhibitor with preference for the PDE4B subtype that raises in skin immune cells, reducing inflammatory cytokines and itch mediators. The action is confined to the skin, with negligible systemic exposure and no central-nervous-system rationale.
receptor fingerprint
PDE4 (PDE4B-preferring, skin-localized)Inhibits
Skin inflammation (atopic dermatitis)Reduces
PruritusRelieves
Inflammatory cytokines and itch mediatorsSuppresses
Evidencehow good the literature is
Human RCTs (skin): in adults, 1% difamilast achieved IGA success of 38.5% versus 12.6% for vehicle; in children, 0.3% and 1% achieved 44.6% and 47.1% versus 18.1%. A systematic review and meta-analysis of five RCTs (over 1,000 patients) confirmed higher success rates and reduced eczema severity with no increase in treatment-related adverse events. Cognition: none.
Safetyrisks and cautions, not medical advice
Mostly mild-to-moderate treatment-emergent adverse events, often less frequent than with vehicle, with possible application-site reactions. Systemic exposure is negligible and it is not emetogenic; unlike oral PDE4 inhibitors.
History
Developed by Otsuka Pharmaceutical as OPA-15406 and approved in Japan in 2021 under the brand Moizerto, difamilast became the first PDE4 inhibitor approved for atopic dermatitis in that country, adding a non-steroidal topical option for eczema.
Reputation
Regarded in dermatology as an effective, well-tolerated non-steroidal topical for eczema, notable for its PDE4B selectivity and rapid effect on itch. It has no standing; and no basis; as a cognitive or nootropic compound.
Subjective profileweighing the evidence above
An approved, effective topical eczema PDE4 inhibitor with a clean safety profile. It has no cognition relevance and is on this list only to complete the PDE4 class.
Resources
This entry is here for reference.
Research
- 1.Difamilast ointment in adult patients with atopic dermatitis: A phase 3 randomized, double-blind, vehicle-controlled trial.
- 2.Difamilast, a selective phosphodiesterase 4 inhibitor, ointment in paediatric patients with atopic dermatitis: a phase III randomized double-blind, vehicle-controlled trial.
- 3.Difamilast for the treatment of atopic dermatitis.
- 4.Clinical efficacy and safety of topical difamilast in the treatment of patients with atopic dermatitis: a systematic review and meta-analysis of randomized controlled trials.
4 listed here; entry last updated August 2026
Reviews
My notesprivate to this device
FAQ
Does difamilast affect the brain or memory?
No. It is a topical eczema drug that stays in the skin with negligible systemic absorption; there is no CNS or cognition evidence. It is listed here only for PDE4-class completeness.
Where is it approved?
It was approved in Japan in 2021 (as Moizerto) for atopic dermatitis in patients aged two years and older.
What makes it different from crisaborole?
Both are non-steroidal topical PDE4 inhibitors for eczema; difamilast is notably selective for the PDE4B subtype.
Notes and cautions
- Possible application-site reactions
- Mostly mild-to-moderate adverse events, often at or below vehicle rates
- No meaningful systemic toxicity