Creator: Help Dementia Editorial Team
Published: 2026-04-11T21:09:38

Reviewed by the Help Dementia Editorial Team — our editors review every article for accuracy against guidance from the National Institute on Aging, the Alzheimer’s Association, and peer-reviewed sources.

Long-acting injection sits at the center of this dementia and brain health question.

Pharmaceutical companies are pursuing long-acting injection formulations as a practical solution to improve Alzheimer’s disease treatment adherence. Rather than requiring frequent office visits or complex daily medication regimens, these injectable therapies can be administered on a weekly, monthly, or quarterly schedule, reducing the burden on patients and caregivers. Three leading candidates—lecanemab, donanemab, and BIIB080—represent different mechanisms and delivery approaches currently being studied or approved for early-stage Alzheimer’s disease. The shift toward long-acting formulations addresses a real challenge in dementia care: ensuring consistent treatment adherence over months and years.

For patients in the early stages of cognitive decline, maintaining medication compliance is critical to preserve cognitive function. Lecanemab, which received FDA acceptance for a weekly subcutaneous formulation in January 2025, exemplifies how this approach offers practical benefits—a single injection each week replaces the previous biweekly intravenous infusions that required clinical visits. This change reflects a broader industry trend recognizing that simplifying treatment schedules directly affects how consistently patients receive therapy. The three main candidates in development differ significantly in their mechanisms of action, dosing schedules, and current approval status. Understanding these differences helps both patients and caregivers evaluate which approaches may become relevant to their care decisions as these medications progress through trials and toward potential FDA approval.

How Do Long-Acting Alzheimer’s Injections Improve Patient Care?
Understanding the Different Mechanisms Behind Long-Acting Treatments
Lecanemab’s Weekly Subcutaneous Route: Advancing an Approved Therapy
Donanemab’s Monthly Infusion Schedule: Balancing Frequency and Efficacy
BIIB080’s Quarterly Intrathecal Route: Targeting Tau in Development
Comparing Injection Routes: Convenience, Safety, and Clinical Considerations
The Broader Pipeline and Future Directions for Long-Acting Therapies
Conclusion

How Do Long-Acting Alzheimer’s Injections Improve Patient Care?

Long-acting injectable formulations offer distinct practical advantages over traditional pill-based or frequent infusion regimens. Lecanemab’s new weekly subcutaneous injection, for instance, eliminates the need for repeated intravenous infusions at specialized clinics. Patients can receive a simple under-the-skin injection at a regular medical office, reducing travel time and treatment disruptions. This is particularly valuable for older adults with limited mobility or those living in rural areas far from specialized memory care centers. The bioequivalence data from Eisai demonstrates that the weekly subcutaneous dose achieves the same amyloid clearance and clinical efficacy as the previous biweekly intravenous formulation, meaning the shift is not a compromise—it delivers equivalent benefit with better accessibility. Donanemab follows a monthly intravenous infusion schedule, which still requires clinical administration but offers less frequent dosing than some earlier Alzheimer’s therapies.

In the Phase 3 TRAILBLAZER-ALZ 2 trial, monthly donanemab infusions slowed cognitive and functional decline by 35% compared to placebo. The data showed that 47% of treated patients experienced no measurable cognitive decline over one year, compared to 29% receiving placebo. For patients at the earliest disease stages, the slowing effect was even more pronounced—60% slowing of decline in those cohorts. While this still requires regular clinic visits, the monthly schedule is manageable for many families who can organize transportation and schedule appointments quarterly. The key limitation of all current long-acting formulations is that they still require some form of clinical administration. Unlike daily pills taken at home, even subcutaneous and intramuscular injections must be delivered by healthcare providers in most cases. This preserves a baseline level of clinical contact and monitoring—which is actually beneficial for early disease detection of side effects—but also means patients cannot simply take responsibility for their own dosing at home.

How Do Long-Acting Alzheimer's Injections Improve Patient Care?

Understanding the Different Mechanisms Behind Long-Acting Treatments

The three leading long-acting formulations represent fundamentally different therapeutic approaches to slowing Alzheimer’s progression. Lecanemab and donanemab both target amyloid-beta protein accumulation in the brain, while BIIB080 takes a completely different approach by targeting tau protein, a separate hallmark of Alzheimer’s pathology. This distinction matters because different patients may respond differently to therapies targeting different disease mechanisms, and having options in the pipeline increases the likelihood that more patients will benefit from treatment. Lecanemab works as a monoclonal antibody that binds to protofibrils—toxic aggregates of amyloid-beta—and helps the immune system clear them from the brain. Four years of continuous LEQEMBI therapy in early Alzheimer’s patients has shown sustained cognitive benefits, suggesting that long-term amyloid reduction produces lasting clinical effects. Donanemab uses a similar anti-amyloid mechanism but with a different antibody design, and achieves its effects with less frequent dosing (monthly versus weekly).

The TRAILBLAZER-ALZ 2 trial found that 40% of donanemab-treated patients showed 40% reduction in activities of daily living decline by 18 months—a meaningful measure of functional preservation that matters to patients managing daily tasks. BIIB080 represents an entirely different mechanism: it is an antisense oligonucleotide that reduces tau protein production by targeting the MAPT mRNA that instructs cells to make tau. In Phase 1b trials, BIIB080 achieved a 56% reduction in cerebrospinal fluid tau and 51% reduction in phosphorylated tau, with effects maintained through quarterly intrathecal injections (delivered directly into the spinal fluid). However, a critical limitation is that tau-targeting therapies are earlier in development. The Phase 2 CELIA trial is currently recruiting 735 participants with mild cognitive impairment or mild dementia across North America, Japan, Australia, and Europe, with results expected within the next 2-3 years. This means amyloid-targeting drugs like lecanemab and donanemab have a multi-year head start in proof of efficacy.

Lecanemab’s Weekly Subcutaneous Route: Advancing an Approved Therapy

Lecanemab arrived on the market as an intravenous infusion approved in 2023, but the weekly subcutaneous formulation represents a significant practical improvement for the same underlying therapy. The FDA accepted the biologics license application in January 2025, with an expected decision by August 31, 2025. Subcutaneous injection is simpler than intravenous infusion from a clinical and logistical standpoint—no need for IV access, shorter appointment times, and potential for future at-home administration under medical supervision. The formulation maintains clinical effectiveness while improving convenience. Eisai’s data demonstrates bioequivalent exposure between the weekly 500 mg subcutaneous injection and the previous biweekly 10 mg/kg intravenous dose, with comparable amyloid clearance and clinical efficacy.

This is not simply a diluted or modified version; the 500 mg dose was carefully calibrated to deliver the same effective drug exposure. Long-term follow-up data shows that four years of continuous LEQEMBI therapy in early Alzheimer’s patients produces sustained cognitive benefits—a critical finding because it suggests that early treatment initiates a disease-slowing process that persists over years, not just months. One limitation worth understanding: the subcutaneous injection still requires healthcare provider administration in most cases. Unlike an oral medication, patients cannot self-administer at home without specific training and authorization. Additionally, some patients may experience local injection site reactions or prefer not to receive injections if they have needle anxiety. The shift from intravenous to subcutaneous represents improved convenience, not elimination of the need for clinical oversight.

Lecanemab's Weekly Subcutaneous Route: Advancing an Approved Therapy

Donanemab’s Monthly Infusion Schedule: Balancing Frequency and Efficacy

Donanemab, marketed as Kisunla, is currently FDA-approved for early Alzheimer’s disease and uses a monthly intravenous infusion schedule. This strikes a practical balance between treatment frequency and therapeutic efficacy. Rather than weekly doses, patients receive monthly infusions, which for many families is more manageable in terms of scheduling, travel, and disruption to daily life. A calendar marking the first Thursday of each month is far simpler than managing weekly appointments. The clinical benefits from the TRAILBLAZER-ALZ 2 Phase 3 trial were substantial. The 35% slowing of overall cognitive and functional decline represents a meaningful preservation of brain health when compared to placebo.

More specifically, 47% of donanemab-treated patients showed no measurable cognitive decline after one year of treatment, versus 29% in the placebo group. For patients in the earliest disease stages—those with amyloid positivity but minimal cognitive symptoms—the effect was even stronger: a 60% slowing of cognitive decline. Additionally, at the 18-month mark, donanemab recipients showed a 40% reduction in decline in activities of daily living, which translates to better preservation of the functional abilities needed for cooking, managing finances, and maintaining independence. However, a significant practical consideration emerged from the trial data: only 52% of participants completed treatment within 12 months, and 72% completed by 18 months. This means that some patients discontinued donanemab before the trial concluded, either due to adverse effects, amyloid-related imaging abnormalities (ARIA), or logistical challenges. While the 35% slowing of decline is impressive, it applies only to patients who persist with treatment. For some patients, the burden of monthly clinic visits or the occurrence of side effects means they cannot or will not sustain long-term therapy, limiting the real-world benefit relative to trial results.

BIIB080’s Quarterly Intrathecal Route: Targeting Tau in Development

BIIB080 represents a newer approach to Alzheimer’s treatment by targeting tau protein rather than amyloid-beta. The drug is an antisense oligonucleotide developed by Biogen and Ionis that reduces tau production by interfering with the gene that instructs cells to make the MAPT protein. In April 2025, BIIB080 received FDA Fast Track designation, which accelerates the review pathway if Phase 2 efficacy is confirmed. The intrathecal route—injection directly into cerebrospinal fluid—allows direct delivery of this large molecule therapy to the brain, bypassing the blood-brain barrier. Phase 1b trial results demonstrate dose-dependent reductions in cerebrospinal fluid biomarkers of tau pathology. The highest-dose cohort achieved 56% reduction in cerebrospinal fluid tau (t-tau) and 51% reduction in phosphorylated tau-181, with effects maintained through quarterly dosing in an open-label extension period.

These biomarker improvements suggest that BIIB080 is successfully reducing tau burden in the brain. The ongoing Phase 2 CELIA trial is enrolling 735 participants with mild cognitive impairment or mild dementia across 54 sites in North America, Japan, Australia, and Europe, testing dosing schedules of every 12 or 24 weeks for 72 weeks. Results from this trial will determine whether biomarker improvements translate into clinical benefit—meaning actual cognitive preservation that patients and families can observe. A significant limitation is that tau-targeting approaches are earlier in clinical development than amyloid-targeting therapies. While BIIB080 shows promise, we do not yet have Phase 3 efficacy data or FDA approval, whereas lecanemab and donanemab are already available to patients. Additionally, intrathecal injection is more invasive than subcutaneous or intravenous routes; it requires a spinal tap or lumbar puncture procedure, which carries small risks of infection or headache. This procedure is less convenient than weekly or monthly infusions and may deter some patients from participating in trials or choosing this therapy in the future, even if it proves effective.

BIIB080's Quarterly Intrathecal Route: Targeting Tau in Development

Comparing Injection Routes: Convenience, Safety, and Clinical Considerations

The three long-acting formulations use different routes of administration, each with distinct tradeoffs. Subcutaneous injection (lecanemab) is the least invasive, requiring only a small needle inserted under the skin for a few seconds. Weekly subcutaneous injections can potentially be administered in an office setting in minutes, with minimal risk. Intravenous infusion (donanemab) is more involved, requiring venous access and typically 30-60 minutes for the infusion, but is well-established in clinical practice and relatively safe when administered by trained staff.

Intrathecal injection (BIIB080) is the most invasive, requiring a lumbar puncture procedure that carries small but real risks of infection, meningitis, or post-lumbar-puncture headache. For patients weighing these options, convenience clearly favors subcutaneous over IV, and IV over intrathecal. However, efficacy data may ultimately outweigh convenience. If Phase 2 data demonstrates that BIIB080’s tau-targeting approach is more effective than amyloid-targeting for certain patient subgroups, some patients may choose the intrathecal route despite its invasiveness. Real-world adoption will likely depend on individual patient preferences, disease characteristics, and willingness to accept procedural burden for therapeutic benefit.

The Broader Pipeline and Future Directions for Long-Acting Therapies

Beyond these three leading candidates, 138 drugs are currently being assessed in 182 clinical trials for Alzheimer’s disease treatment, according to the 2025 Alzheimer’s disease drug development pipeline. This substantial pipeline suggests that multiple therapeutic approaches will likely reach patients in coming years, offering options suited to different disease stages and patient characteristics. The trend toward long-acting formulations reflects industry recognition that improving adherence and reducing treatment burden are essential to translating scientific efficacy into real-world clinical benefit.

The convergence of long-acting formulations with multiple mechanisms of action—amyloid-targeting, tau-targeting, neuroinflammation-targeting, and others—creates potential for combination therapies in the future. Just as cancer and HIV treatment now frequently use drug combinations to prevent resistance and improve outcomes, Alzheimer’s disease treatment may evolve toward multi-drug regimens targeting different pathological processes simultaneously. Long-acting injectable formulations make such combinations more feasible by reducing total treatment burden compared to multiple daily pills. The next 2-3 years will reveal whether tau-targeting approaches like BIIB080 deliver clinical benefits, which will determine whether multi-mechanism approaches become viable.

Conclusion

Long-acting injection formulations represent a practical evolution in Alzheimer’s disease treatment that addresses a central challenge in dementia care: ensuring consistent therapy adherence over years. Lecanemab’s newly approved weekly subcutaneous formulation, donanemab’s monthly intravenous infusion, and BIIB080’s quarterly intrathecal injection each offer different balances of convenience, invasiveness, and therapeutic mechanism.

For patients in early Alzheimer’s disease, these options provide meaningful opportunities to slow cognitive decline—with 35-60% slowing of progression documented in clinical trials—while reducing the logistical burden compared to daily medications. Families and patients facing these treatment decisions should understand that perfect adherence to these long-acting therapies is important; the clinical benefits observed in trials apply primarily to patients who persist with treatment over months and years. Discussing these options with a neurologist or memory care specialist, understanding individual disease characteristics and personal preferences regarding invasiveness, and maintaining realistic expectations about what slowing cognitive decline means for daily life will help guide the choice of therapy when these medications become available through standard care pathways.