The Founder · Est. 2019

A pharmacist with a compounding bench and 82 stubborn opinions.

Dr. Marthe Janssen spent twelve years behind a counter in Rotterdam watching customers hand her supplement bottles with ingredients she couldn't recommend. In 2019 she started making the versions she'd actually dispense.

PharmD · Utrecht, 2011 Hospital pharmacy · 7 years Compounding certification
V
Dr. Marthe Janssen
PharmD · Founder
Rotterdam · 2026
— Marthe
Everything on this site
was formulated or approved by Dr. Janssen personally
Origin · In her own words

I started Vesper because I got tired of lying with my silence.

For seven years I worked behind a pharmacy counter in Rotterdam. People would come in clutching supplement bottles they'd ordered online — often expensive, often well-reviewed, almost always wrong. Under-dosed magnesium oxide for sleep. Gummies sweetened with sugar alcohols that triggered the exact digestive issues they were meant to fix. "Prenatal" vitamins with folic acid instead of folate, in amounts too low to matter.

I'd smile. I'd say "this won't hurt you." I'd watch them leave. And I'd go home and stew.

The supplement industry in 2018 was — and still is — a pharmacist's nightmare. Label claims aren't verified. "Clinical dose" means nothing legally. A company can put 25mg of an ingredient studied at 400mg on their label and call it the same thing. The worst part: the good ingredients exist. They're just not in the bottles customers are buying.

I wanted a shelf of supplements I could hand to my mother, my sister, a stranger — and be certain, clinically, that the dose on the label was the dose in the capsule and the dose that would actually do something. — on why Vesper exists

So in the winter of 2019 I rented a small compounding space above a bakery on Witte de Withstraat, bought a cGMP-certified encapsulator, and made one formula — magnesium glycinate, chelated, 400mg, third-party tested. I sold it to fourteen of my regular customers. Within a month they were asking for more things. Glycine. B-complex. A better prenatal.

Six years later there are eighty-two formulas and a team of four. We still test every batch. I still write every label. And every person who emails us asking for advice gets a real answer from a pharmacist — usually me, sometimes my colleague Elise who joined in 2023.

It's not scalable. That's the point.

The long, unglamorous version.

2011

PharmD · Utrecht University

Graduated top of her cohort. Thesis on bioavailability differences in magnesium forms — the research that would, eight years later, become Formula N° 01.

2012–18

Hospital pharmacist · Erasmus MC

Seven years in acute care pharmacy. Ran the IV compounding unit from 2015. Saw firsthand what evidence-based dosing looks like — and why consumer supplements almost never meet that bar.

2019

Vesper · Formula N° 01

Rented 22 square meters above Bakkerij Van den Berg. Compounded magnesium glycinate for fourteen regulars. The rest of the apothecary was built one complaint at a time.

2021

Batch testing partnership

Every batch independently assayed by Eurofins for identity, potency, heavy metals, and microbial contamination. Results published on each product page. Always. No exceptions.

2023

Dr. Elise Bakker joins

Second pharmacist. PharmD Leiden. Focus on women's health formulary. Started the prenatal line and rewrote our entire menstrual-cycle section.

2026

82 formulas · 11,400 customers

Still small-batch. Still Rotterdam. Still pharmacist-answered. No ambition to change any of that.

Credential · 01
PharmD · Utrecht · 2011

Six-year doctoral pharmacy program. Board certified by the Koninklijke Nederlandse Maatschappij ter bevordering der Pharmacie.

Credential · 02
Compounding certification

Certified sterile and non-sterile compounding pharmacist. All formulas developed under cGMP conditions at our Rotterdam facility.

Credential · 03
No industry advisory board

Dr. Janssen does not sit on any supplement-industry advisory boards and accepts no payment or incentive for ingredient selection. Ever.

Three rules · Non-negotiable

The three rules we haven't broken once in six years.

01

Clinical dose or not at all.

If the research was done at 400mg, the bottle contains 400mg. Not 200 with a "proprietary blend" footnote.

02

The form that works.

Glycinate, not oxide. Methylfolate, not folic acid. Triglyceride fish oil, not ethyl ester. These details are the whole game.

03

A pharmacist answers every email.

Usually me. Sometimes Elise. Never a chatbot, never a "wellness advisor," never a script. If you ask, you get an answer from someone who reads studies for a living.

"If I wouldn't hand it to my mother, it doesn't go on the shelf."
— Marthe
Dr. Marthe Janssen · PharmD · Founder
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