Cannabis Potency Guide for Medical Patients
This guide helps medical patients understand cannabis potency and choose the right strain for their needs.
Cannabis potency in one paragraph
Potency is the concentration of active cannabinoids in a product, written as a percentage of total weight. Dispensary flower in the US typically tests between 15% and 25% THC. CBD-dominant flower usually lands between 10% and 20% CBD. Concentrates and vape cartridges run 60% to 90% THC. Those numbers tell you how much cannabinoid sits in the material, not how high you will get. Route of consumption, tolerance, and your own body chemistry change the outcome more than a few percentage points do.
What a percentage means in milligrams
Percentages get easier to use once you convert them. One gram is 1,000 mg, so every 1% of THC equals about 10 mg of THC in that gram.
Cannabis Potency Guide: Understanding Cost
- 20% THC flower, 1 gram: roughly 200 mg THC in the jar
- 15% THC flower, 0.5 gram: roughly 75 mg
- 80% THC cartridge, 0.5 gram: roughly 400 mg
You absorb a fraction of that. Inhaled THC bioavailability is often estimated at 10% to 30%. Oral bioavailability is lower and far more variable, somewhere around 4% to 20%, and the liver converts much of it into 11-hydroxy-THC, a metabolite that crosses into the brain more easily and feels different from smoked THC. That gap explains why a 10 mg edible and a few puffs of 20% flower are not comparable experiences.
THCA, THC, and the number the label leaves out
Raw cannabis does not contain much THC. It contains THCA, the acidic form, which becomes THC when you apply heat through smoking, vaping, or decarboxylation in an oven. THCA has a heavier molecule, so the conversion loses mass. Multiply THCA by 0.877 and add any THC already present to get total THC.
A jar listing 0.5% THC and 22% THCA works out to about 19.8% total THC. Same math for CBD: CBDA multiplied by 0.877, plus CBD. If a flower label shows only THCA and you want to compare it against a product that lists total THC, do the conversion first. The same strain can look 5 points stronger or weaker depending on which number the brand chose to print.
Why a higher THC number is not a highness score
Three reasons.
- Delivery. A 30% flower joint and a 30% flower bong hit put different amounts into your bloodstream.
- Other compounds. Myrcene, limonene, caryophyllene, and minor cannabinoids such as CBG and CBC may shape the experience. The entourage effect is a popular idea, but human trials testing it are thin, so treat strong claims with caution.
- Tolerance. Daily users need more to feel the same thing. A 32% strain can do less for a heavy user than 18% does for a first-timer.
There is also a practical ceiling. Many users cannot reliably pick out 22% flower from 28% flower in a side-by-side, and at the top end the difference you notice often comes from terpenes and cure quality rather than the last few points.
CBD potency and ratios
CBD does not activate CB1 receptors the way THC does, so it does not produce a high. Dose still matters, because effect scales with how much you take.
Ratios are the useful shorthand. A 1:1 product has equal THC and CBD. A 2:1 has twice as much CBD as THC. A 20:1 is nearly all CBD. People who find THC edgy often prefer 1:1 or 2:1, where the CBD seems to soften the sharper edges of the THC. CBD-dominant flower sold as hemp, under 0.3% THC, is a separate product category with its own rules.
CBD oil is dosed in milligrams per milliliter, not percent. A 30 mL bottle holding 1,500 mg total CBD is 50 mg per mL, and a full dropper is usually about 1 mL.
Picking a potency that fits
- First time: 10% to 15% flower, one or two puffs. For edibles, 2.5 mg.
- Occasional: 15% to 20% flower, or a 5 to 10 mg edible.
- Regular: 20% to 25% flower, with edible doses built from your own history.
- Concentrates: start with a rice-grain amount. Treat one dab as several times the dose of a flower hit.
With edibles, wait two hours before taking more. The delay is where most rough nights start.
Labels are not lab grade
Independent testing has found mismatches between what is printed and what is inside. A JAMA study of edible products found THC content that often differed from the label, in both directions and sometimes by a wide margin. Flower labels tend to be closer, but they still drift depending on the lab, the sample, and the batch. Look for a batch-specific certificate of analysis, a harvest or packaging date, and a stated terpene profile. Older flower loses potency as THC degrades into CBN.
Bottom line
Potency is a starting point, not a promise. Read total THC rather than THCA, convert percentages to milligrams, match the number to your tolerance, and move slowly with edibles. A well-grown 18% strain you enjoy beats a harsh 30% one you do not.