Combining CBD Products: Counting The Day's Milligrams

Two bottles, one running figure?

Does an oil in the morning plus a capsule at night count as one amount, or two? The molecule answers that. Cannabidiol is the same compound whether it arrives as drops under the tongue, a softgel with breakfast, or a capsule you swallow with water. The carrier changes. The active ingredient doesn't.

So the figure printed on a pack belongs to that pack. It was set for one product, and it knows nothing about what else sits in your cupboard. Bring a second product into the routine and the arithmetic becomes yours: milligrams from both go into the same running total for the day.

There's a reason to be careful with the maths rather than the impression. The 2018 systematic review by Millar gathered the human pharmacokinetic studies on cannabidiol, the ones that measure how much of it appears in blood and when, and the spread between those studies was wide [1]. Three factors were named as determinants of the measured concentrations: route of administration, formulation, and whether food was taken at the same time [1].

• One compound, many carriers: oils, capsules and drinks all deliver cannabidiol, so they land in the same daily column.
• A label maximum describes one product on its own, not the sum of everything you use that day.
• Route, formulation and food eaten alongside were listed as determinants of the blood concentrations measured in people [1].
• Between-study variation in those human measurements was wide, so no single tidy number covers everybody [1].

Work in milligrams, not in habits

The unit that travels between formats is the milligram. Percentages don't add up across a shelf, and "one of each" isn't a figure at all. So the first job is to turn every product in your routine into milligrams per serving, then add the servings you actually take.

Oils make this simple to look up: the bottle states total milligrams of cannabidiol, and the milligrams per drop follow from the volume. Capsules and softgels arrive pre-portioned, so the milligram figure is printed on the pack. Add the two figures and you have your day in one number. That number is what the label maximum applies to. Write it down for a week if the routine is new, and the picture stops being guesswork.

Concentration deserves a plain word too. A 20% oil holds more cannabidiol per drop than a 4% oil, and that's the whole difference: fewer drops for the same milligrams. It's a spec on the bottle, nothing more.

Then there's the paperwork. Since 2014 we've published independent batch analyses, so if a bottle says 10%, the report is where you check it. When you're adding two products together, verified content on both sides is what makes your arithmetic worth doing.

• Milligrams per serving for each product, taken from the label rather than estimated.
• Servings per day for each, as you actually take them, not as you intended to.
• One sum for the day, checked against the maximum stated on the packs.
• A batch report for every bottle in the routine, so the numbers you're adding are verified ones.

Skin keeps its own column

What the 2004 permeation work measured

Stinchcomb and colleagues ran cannabidiol, cannabinol and delta-8-tetrahydrocannabinol through human skin samples in 2004, and the transfer through the skin barrier was slow for all three [2]. Three cannabinoids, one tissue model, and a rate that stayed low in each case [2]. Worth being precise about what that experiment tracked: movement across skin under laboratory conditions [2]. Not blood levels in a living person over a day, and not a comparison with swallowing a capsule. Skin is a barrier before it's a route, and the 2004 measurements describe how reluctant a barrier it is [2]. That's a laboratory endpoint, and it's the kind of detail that decides how you count a topical. Useful, and limited, in the same breath.

Applied where you put it

A topical goes onto one patch of skin: a knee, a shoulder, the back of a hand. Going by the 2004 permeation data, its action stays largely local, which is why many people keep a balm in a column of its own rather than in the swallowed total [2]. Read that as an interpretation of a laboratory measurement, not as a finding from a human trial. If your own approach is to count everything, counting a cream too costs you nothing except a slightly lower figure elsewhere. Both approaches are defensible. The one thing worth avoiding is assuming the answer without knowing which evidence you're leaning on. A balm on a shoulder and drops under the tongue are two different questions, and the 2004 work only answers one of them [2].

The shape of the evidence

Millar's 2018 review is a systematic one, meaning the authors defined a question, searched the literature and reported what they found rather than picking favourites, and what they found on cannabidiol in humans came mostly from single products given under controlled conditions [1]. One preparation. One route. Measured windows. That design is how pharmacokinetics gets done, and it's also why the numbers travel poorly to a day that includes an oil at breakfast, a capsule after dinner and a balm in between.

Add the variation. Between-study differences in the measured blood concentrations were wide, and the review points to route of administration, formulation and food co-ingestion as determinants of that spread [1]. Each of those changes when you combine formats. Drops held under the tongue and a softgel swallowed with a meal are not the same route, and a meal in the picture is exactly the food variable named in the review [1].

So the honest position: the milligram arithmetic is straightforward, and the pharmacokinetics of two formats in the same day is not something the human literature has pinned down [1]. We don't know yet how a combined routine compares with the controlled single-product studies, and nothing about the 2004 skin work fills that gap either, since its endpoint was movement across a tissue sample in the lab [2].

That's not a reason to avoid combining. It's a reason to keep the counting simple and the expectations modest, and to change one thing at a time when something in the routine changes.

Before the second bottle joins in

Start with the two labels side by side and write down the milligrams. Not the percentages, not the number of drops, the milligrams. That single figure is the thing that carries across formats, and it's the figure a maximum on a pack is written against.

Food and timing are worth a line in the same note. The 2018 review names food co-ingestion as one of the determinants of the concentrations measured in people, so a capsule with dinner and drops on an empty stomach are two different conditions on paper [1]. You don't have to optimise anything. Knowing which day was which is enough.

If you take prescription medication, or you're pregnant, breastfeeding or managing a diagnosed condition, the conversation belongs with your doctor or pharmacist before a second cannabinoid product goes into the routine. Bring the labels. A pharmacist can read a milligram figure far faster than a description of a bottle.

Then the boring, useful part: the batch report. Since 2014 the standard here has been that a stated percentage should be checkable, which is why every batch is analysed independently. If you're combining two products, that's two reports, and both are published. A label and a report that agree are the base your arithmetic sits on. Our products are non-intoxicating and stay within the legal THC limits, and putting an oil and a capsule in the same day doesn't change that specification.

Start low, go slow, and keep the total in one place. Nature, made precise, works best when you know both numbers you're adding.