---
title: 'Senior Principal Scientist, Drug Substance at Loyal'
canonical: 'https://feeny.ai/job/senior-principal-scientist-drug-substance-loyal-united-states-6fv71bjzb5w0'
type: 'job'
last_seen: '2026-09-10'
---

# Senior Principal Scientist, Drug Substance at Loyal

- **Company:** Loyal
- **Location:** United States
- **Work type:** remote
- **Posted:** 2026-06-29
- **Last confirmed live:** 2026-09-10
- **Apply:** https://job-boards.greenhouse.io/loyal36/jobs/5285476008

## Job description

## About Loyal

Loyal is a clinical-stage veterinary medicine company developing longevity drugs for dogs. Our mission is to help dogs live longer, healthier lives.

We're pioneering a new category of veterinary prescription drugs that proactively and preventatively target the underlying drivers of aging, delaying the onset of disease and preserving quality of life as dogs age. We've already made significant progress in our mission to develop the first FDA-approved drugs to extend canine lifespan: as of early 2026 we've completed two of three major FDA review sections for our lead program, LOY-002, and are targeting submission of the third and final section later this year.

Loyal is a[well-funded startup](https://loyal.com/posts/125m-to-extend-dog-lifespan) with teams of scientists, veterinarians, engineers, operators, and creatives. You'll help us continue on our path of earning FDA approval for the first lifespan extension medicine for any species — and change what's possible for the dogs we love.

## About the role

Loyal is seeking a Senior Principal Scientist, Drug Substance to serve as the technical leader for drug substance process development and manufacturing from early development through commercialization. This high-impact, externally-facing role will drive drug substance process development and manufacturing, and deliver flawless execution across CDMO partners while serving as the internal subject matter expert informing cross-functional decision-making and long-term development strategy across Loyal's growing pipeline.

You will be reporting to our VP of Manufacturing

## Your daily work will include

- Lead end-to-end drug substance process development and manufacturing  for small molecule APIs  from synthetic route assessment and impurity control through scale-up, technology transfer, and commercial manufacturing readiness at CDMOs.
- Serve as the primary technical interface with drug substance CDMOs spanning partner selection, day-to-day oversight, troubleshooting, PAI preparation and performance management; ensure drug substance supply continuity, including second source qualification and starting material supply risk strategy, in support of clinical and commercial manufacturing.
- Lead RSM designation, ICH Q11 assessments, impurity fate and purge strategies and ICH M7 mutagenic impurity risk assessments; establish CQAs, CPPs, and ICH Q6A-aligned control strategies.
- Lead drug substance process validation from PPQ protocol development through batch execution and CPP/CQA verification; align PPQ timelines and batch disposition with drug product process validation and registration batch campaigns.
- Author, review, and approve drug substance CMC sections for regulatory submissions (VMF, INAD/NADA); represent drug substance CMC in agency interactions and ensure a technically integrated and consistent regulatory package.
- Partner with drug product development to translate drug substance CQAs into formulation design, excipient selection, container closure strategy and final dosage form decisions.
- Partner with analytical development to define method development, qualification, and validation strategy for drug substance release and stability testing.
- Partner with Quality to align drug substance specifications, batch disposition, and GMP compliance across CDMOs, and to support inspection and regulatory submission readiness.
- Manage drug substance post-approval change control strategy for manufacturing changes at CDMOs.

## About you

- Ph.D. in Chemistry, Chemical Engineering, Biochemistry, or a related discipline.
- 12+ years of industry experience in drug substance process development and manufacturing, with demonstrated ownership from early development through regulatory submission and commercialization phase.
- Hands-on expertise in small molecule API process development, including synthetic process understanding, impurity profiling, ICH Q11 RSM assessment, and ICH M7 mutagenic impurity control.
- Proven experience selecting, managing, and technically overseeing CDMOs for small molecule drug substance development, scale-up, technology transfer and PPQ.
- Demonstrated experience authoring and defending drug substance CMC regulatory submissions (INAD/NADA, VMF or equivalent) and interacting with regulatory agencies on CMC questions.
- Deep knowledge of applicable regulatory frameworks: ICH Q7, Q8, Q9, Q10, Q11, Q6A, M7, and relevant VICH guidelines for veterinary drug substances.
- Demonstrated ability to operate effectively in a dynamic, fast-paced startup environment with a high degree of autonomy and accountability.
- Experience with large biomolecule drug substance development (peptides, proteins, or other biological entities) preferred but not required.
- Veterinary dosage form experience preferred but not required.

Salary Range: $175,000 - $230,000

Loyal benefits

- Full-coverage health insurance — medical, dental and vision — for you and your dependents
- $1,000 home office equipment stipend
- $1,200/year learning budget for books, courses, etc.
- $250/month wellness budget for gym, cleaners, spa, food, etc.
- All 3-day weekends are turned into 4-day weekends 🎉
- Unlimited vacation and paid holidays
- Paw-ternity leave — adopt a dog and get a day off with your new family member 🐶
- Competitive salary
- Company equity options grant for new hires

Loyal is founded and led by a first-gen female CEO and is proud to be an equal opportunity employer. We do not discriminate against applicants based on gender, race or color, ethnicity or national origin, age, disability, religion, sexual orientation, gender identity or expression, veteran status, or any other applicable characteristics protected by law.

## Our values

Moonshots, derisked methodically

Bringing the first longevity drug to market is an extremely difficult technical and social pursuit. To achieve this we must take bigger bets than the field has historically made, paired with the technical rigor to de-risk them step by step. We plan on both short and extremely long timescales, and we have the conviction to see our vision through to success or failure.

Opportunity is at the intersection

We lean into combining disciplines, expertise, and perspectives not normally adjacent. We design our organization to facilitate cross-pollination and cross-collaboration. We reject silos.

Expertise without ego

Titles do not determine who has a voice. We push back on each other, ask questions instead of issuing orders, and try to prove ourselves wrong. We are emotionally attached to the outcome, not our personal hypotheses, and welcome being challenged instead of treating it as a threat.

High agency, high humility

Most of what we're doing has never been done before, so we can't rely on established precedents to guide our way. We move forward to generate clarity, build strategies resilient to the fact that we don't know what we don't know, and design small experiments where we can fail safely, without jeopardizing the bigger mission.

Lead with transparency and context

We proactively and consistently share the why behind our strategy - not just the what - because we believe sharing context enables great people to make great decisions.

Empathy and respect for all life

Our patients are not just numbers. We deeply respect the value of every life, large and small and take our ethical responsibility to the families we treat extremely seriously.

## About Loyal

## Company Overview
- **One-liner**: Loyal is a clinical-stage veterinary medicine company developing the first FDA-approved drugs intended to extend the lifespan and healthspan of dogs.
- **Entity Type**: Private (Series C)
- **Headquarters**: San Francisco, California, United States
- **Founded**: 2020
- **Founders**: Celine Halioua

## Core Business
- **Primary industry**: Veterinary Medicine / Animal Health Biotechnology
- **Target customers**: B2B (veterinary clinics) and B2C (dog owners)
- **Mission**: To help dogs live longer, healthier lives by developing drugs that target the underlying processes of aging.

## Products & Services
For each major offering:
- **[LOY-002](https://loyal.com)**: A once-daily pill targeting age-associated metabolic dysfunction in senior dogs (ages 10+, 14+ lb). It is the lead drug program and has completed the second of three major requirements for FDA conditional approval. Designed to extend lifespan and maintain quality of life.
- **[LOY-001](https://loyal.com)**: A drug program targeting age-associated metabolic dysfunction (currently in earlier stages of development).
- **Loyal Learning Hub**: A free library of RACE-approved continuing education courses for veterinary teams to improve care for senior dogs.

## Market Standing
- **Valuation/Market Cap**: Not disclosed
- **Total Funding**: $238.0M across six rounds
  - Series C (2026-02-01): $100M [LinkedIn](https://www.linkedin.com/company/loyalfordogs)
  - Series B (2025-02-01): $22M
  - Series B (2024-03-01): $45M
  - Series A (2022-04-01): $13M
  - Series A (2021-09-01): $27M
- **Key Metric**: Annual Revenue of $2.0M (pre-commercial stage) [LinkedIn](https://www.linkedin.com/company/loyalfordogs)
- **Notable Investors/Partners**: 2 investors in Series B (2025), 3 investors in Series C (2026) [LinkedIn](https://www.linkedin.com/company/loyalfordogs)
- **Growth Signals**: Headcount grew 53.3% year-over-year to 71 employees [LinkedIn](https://www.linkedin.com/company/loyalfordogs). Targeting commercial launch of LOY-002 in 2027. Completed 2/3 major FDA review sections for LOY-002 as of early 2026 [Greenhouse](https://job-boards.greenhouse.io/loyal36/jobs/5235415008).

## Competitive Advantages
- **First-to-market**: Pioneering the first FDA-approved lifespan extension drug for any species, creating a new category in veterinary prescription medicine.
- **Regulatory moat**: Achieving FDA conditional approval for a longevity drug is an extremely difficult technical and regulatory pursuit, creating a significant barrier to entry.
- **Targeting aging itself**: Unlike most veterinary drugs that treat specific diseases, Loyal targets the underlying drivers of aging to delay the onset of multiple age-related conditions.
- **Strong clinical trial infrastructure**: 70 veterinary clinics enrolled in the STAY clinical trial, with over 1,317 dogs accepted [loyal.com](https://loyal.com).

## Strategic Focus
- **Regulatory approval**: Completing the third and final FDA review section for LOY-002 and targeting submission in late 2026 [Greenhouse](https://job-boards.greenhouse.io/loyal36/jobs/5235415008).
- **Commercial launch preparation**: Scaling the company from ~70 to ~150 people, building a customer service organization, and leading product distribution platform buildout for prescription drug distribution, targeting a 2027 launch [Greenhouse](https://job-boards.greenhouse.io/loyal36/jobs/5235415008).
- **AI-leveraged efficiency**: Deploying AI tooling across operations, finance, recruiting, and customer service to scale leverage with the team [Greenhouse](https://job-boards.greenhouse.io/loyal36/jobs/5235415008).
- **Pipeline expansion**: Developing a portfolio of three drug programs (LOY-002, LOY-001, and others) targeting different aspects of aging.

## Why Work Here
- **Mission-driven**: The company is deeply committed to helping dogs live longer, healthier lives — a compelling purpose for many job seekers.
- **Culture**: Values include "Empathy and respect for all life," "Expertise without ego," "High agency, high humility," and "Lead with transparency and context" [loyal.com/careers](https://loyal.com/careers).
- **Remote-first**: All open roles are listed as "Remote - US" [Greenhouse](https://job-boards.greenhouse.io/loyal36).
- **Generous benefits** [loyal.com/careers](https://loyal.com/careers):
  - Full-coverage health insurance (medical, dental, vision) for you and dependents
  - $1,000 home office equipment stipend
  - $1,200/year learning budget
  - $250/month wellness budget (gym, cleaners, spa, food)
  - All 3-day weekends turned into 4-day weekends
  - Unlimited vacation and paid holidays
  - "Paw-ternity leave" — adopt a dog and get a day off
  - Annual company retreat at beautiful locations (recently: Tahoe, Cape Cod)
  - Competitive salary and equity options grant
- **Leadership**: Founded and led by a first-gen female CEO, Celine Halioua. The company is an equal opportunity employer.
- **Growth opportunity**: As a well-funded startup targeting a 2027 commercial launch, there is significant potential for career growth and impact.

## Sources
1. [loyal.com](https://loyal.com)
2. [loyal.com/careers](https://loyal.com/careers)
3. [LinkedIn - Loyal](https://www.linkedin.com/company/loyalfordogs)
4. [Greenhouse - Loyal Jobs](https://job-boards.greenhouse.io/loyal36)
5. [Greenhouse - COO Job Posting](https://job-boards.greenhouse.io/loyal36/jobs/5235415008)

## Other roles at Loyal

- [Senior Statistician, Research & Development](https://feeny.ai/job/senior-statistician-research-development-loyal-united-states-0r3knng5j7zr) — United States
- [Director, FP&A](https://feeny.ai/job/director-fp-a-loyal-united-states-nb572c2e9bfg) — United States
- [Senior Associate Specialist, Regulatory Operations](https://feeny.ai/job/senior-associate-specialist-regulatory-operations-loyal-united-states-bd9kwj4pttpt) — United States
- [Principal Analytical QA Specialist, Drug Substance](https://feeny.ai/job/principal-analytical-qa-specialist-drug-substance-loyal-united-states-hva9wqft24jn) — United States
- [Director, Regulatory Affairs - Clinical](https://feeny.ai/job/director-regulatory-affairs-clinical-loyal-united-states-1j9et5dxrqdn) — United States