The honest version of this page: we are a retention agency, we appear on this list, and you should treat our entry with the same skepticism as any agency ranking itself. What makes the list useful anyway is that supplement email is a specialist problem, most general agencies are a poor fit, and the shops we would actually put a supplement brand in front of are few enough to name.
Why specialization matters in this vertical specifically: replenishment timing per SKU, suppression between subscribers and one-time buyers, and FTC substantiation exposure in copy. The FTC sent penalty offense letters to roughly 670 health product marketers in one round alone, with penalties that can exceed $50,000 per violation. A generalist can run your campaigns. Those three constraints are where accounts actually win or lose, and they require having done it before.
How this list was put together
This is a practitioner's list, not an aggregation. These are agencies whose work we have seen and rate from operating in the same market, not names pulled from directories. Nobody paid to be here, there is no ranking order, and we include ourselves with the same fit note we give everyone else so you can judge the list rather than trust it.
Agencies we rate for supplement brands
Magnet Monster
A Klaviyo Elite Master partner running full-service retention (email, SMS, WhatsApp, direct mail) with 300+ DTC brands behind them and deep subscription and lifecycle work. If you want a large, proven retention shop with real process, this is the profile.
Underground Ecom
A UK-based Klaviyo Elite Master partner and Klaviyo's Agency Partner of the Year EMEA 2025, built for growth-stage DTC brands, with a data-led approach that ties actions to projected revenue. A fit if you want rigor and reporting discipline at scale.
Retention Harbor
That is us. We build and run Klaviyo retention systems for DTC brands, supplements among them, with the per-SKU replenishment and subscription-suppression architecture described in our supplement setup guide. We are the wrong fit if you want paid media and email under one roof, and the right conversation if retention is the specific thing you are hiring for.
How to actually choose between them
Ignore the rankings, including this one, and ask each agency the same three vertical questions:
- How would you set replenishment timing for our specific SKUs, and from what data?
- How do you keep active subscribers out of flows written for one-time buyers?
- What is your process for keeping claims inside FTC substantiation lines?
The generalists answer all three generically. The specialists answer with specifics from accounts they have run. Our full question list is in the supplement agency guide, and the 30-minute self-audit worth running first is here.
What to include in your first inquiry
You will get a sharper first call from every agency on this list if your inquiry includes five facts: monthly revenue range, list size, subscription platform and share of revenue on subscription, your top three SKUs with their supply cycles, and whether copy currently goes through compliance review. Those five let a real specialist arrive with a point of view instead of a deck.
Frequently asked questions
What does a supplement-focused email agency cost?
Mid-market retention retainers generally run $6,000 to $12,000 a month, with fractional specialists below that. Be wary of quotes produced before anyone has looked inside your account. For the full cost comparison against hiring in-house, see our in-house vs agency guide.
Do we need a supplement specialist, or is DTC experience enough?
DTC experience covers most of the work. The three vertical questions above are the gap, and an otherwise strong agency that has never handled compliance review or replenishment timing will learn on your account.
Should the agency also run our SMS?
Usually yes, once email architecture is sound. Split ownership of email and SMS produces double-messaging on exactly the flows where timing matters most.
How should we run the selection process?
Run the self-audit first, take calls with two or three from this list, ask all of them the same three questions, and weight the specificity of the answers over the polish of the deck.
Sources
- Magnet Monster. Klaviyo Elite Master retention agency.
- Underground Ecom. Klaviyo Elite Master partner, EMEA Agency Partner of the Year 2025.
- FTC. Penalty offense letters to health product marketers.