Tools

Jump to section ▼ What we DO What we DON’T Where this leaves us Editorial independence Updates and corrections Contact Editorial standards How We Review Supplements This is the canonical source. The same content gets published as a static HTML page at usefulvitamins.com/how-we-review-supplements/. Every DTC review article links here via the methodology callout block. What

DTC Greens Powder Cost & Ingredient Comparator | UsefulVitamins DTC Greens Powder Cost & Ingredient Comparator Not all greens powders are created equal — or priced the same. This tool filters 10 products (4 DTC brands, 6 Amazon picks) by your monthly budget, dietary needs, and health goal, then surfaces the top 3 by value

Calculate the latest time you should drink your last caffeinated beverage based on your target bedtime, your caffeine sensitivity, and the dose. Built on a pharmacokinetic decay model with Drake 2013 sleep-disruption evidence as the threshold. Math, not medical advice. Caffeine half-life varies a lot between people. Average is about 5 hours, but pregnancy can

Estimate the daily vitamin D3 dose needed to raise your serum 25(OH)D from a known baseline to a target level. Based on Heaney 2003 dose-response (~100 IU/day per 1 ng/mL increase, weight-adjusted). Math, not medical advice. Get a serum 25(OH)D blood test before high-dose supplementation. The Endocrine Society recommends measuring 25(OH)D in adults at risk

Convert vitamin D between micrograms (mcg) and International Units (IU). Works for both D3 (cholecalciferol) and D2 (ergocalciferol) — they share the same conversion factor. Math, not medical advice. 1 mcg vitamin D = 40 IU. The conversion factor is fixed by FDA / IOM definition and applies equally to D3 (cholecalciferol) and D2 (ergocalciferol).

Compare 2 or 3 peptides head-to-head: FDA status, primary indication, typical dose, evidence level, monthly cost, side effects, and the deep-dive article on each one. Comparison rows are based on FDA prescribing information, manufacturer-published prices, and the published RCT literature as of 2026-04-27. Not medical advice — verify with your prescriber before starting any peptide.

Track your GLP-1 dose-escalation schedule from FDA-labeled titration. Pick your drug and start date — the tool shows your current week, current dose, next escalation date, and total weeks to maintenance. Schedules below come directly from the FDA prescribing information. Your prescriber may slow titration if you experience side effects, or hold a dose longer

Find your daily collagen target based on what you’re trying to support — skin, joints, or muscle. Doses below come from human RCTs, not marketing copy. Math, not medical advice. Collagen is a supplement, not a drug. Doses below are typical RCT amounts that produced measurable effects in published studies. Most studies use flat doses

Estimate your monthly out-of-pocket cost for FDA-approved GLP-1 medications. Covers Wegovy, Ozempic, Mounjaro, Zepbound, Saxenda, Trulicity, and Victoza. Math, not medical or financial advice. Prices change frequently. Manufacturer list prices, savings-card terms, and insurance formularies all shift quarterly. The numbers here are 2025 / early-2026 estimates based on publicly disclosed sources. Verify the actual cost