The short answer
If you're shopping for seizure support, start at 20:1 or higher in favor of CBD. That means 20 mg of CBD for every 1 mg of THC, or less. Pure CBD sits at the far end of that scale, and that's where the strongest evidence lives. The prescription version the FDA approved for Dravet, Lennox-Gastaut, and tuberous sclerosis is CBD with no THC in it at all.
Everything else on the shelf is a step down in evidence, not necessarily in usefulness. Here's how I'd rank the options.
What I'd pick first: a 20:1 to 25:1 CBD tincture
A tincture wins for one boring reason. You can change the dose by a drop. Gummies and vapes lock you into a fixed amount, and when you're tracking seizures day by day against a new cannabinoid, control matters more than convenience.
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Look for a full-spectrum or broad-spectrum oil with a batch-specific certificate of analysis, often called a COA. Full spectrum keeps trace THC and minor cannabinoids. Broad spectrum strips the THC out. Both are reasonable choices. What isn't reasonable is a bottle that lists a proprietary blend and no milligrams.
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Ratio math, so the label stops being confusing: a 30 mL bottle with 1,500 mg CBD and 75 mg THC is 20:1. One milliliter dropper holds 50 mg CBD and 2.5 mg THC.
Options after that
1. THC-free CBD isolate
Zero psychoactivity and zero risk of a positive drug test. The tradeoff is that you lose the minor cannabinoids and terpenes some people credit for the entourage effect. If you're starting from nothing, this is the cleanest single variable to test.
2. A 10:1 CBD to THC oil
A middle step. Enough THC to feel something at higher doses, still CBD-dominant. Some people move here after a month or two at 20:1 and a stable seizure log. Change one thing at a time, or you won't know what shifted.
3. 1:1 and THC-forward products
Not a starting point. THC can lower seizure threshold, and the clinical literature on THC and epilepsy is thin and mixed. If a neurologist wants THC in the mix, that's a different conversation than a budtender recommendation. I'd treat 1:1 as a later, supervised experiment, not a first buy.
Five things to check before you pay
- Total CBD in milligrams per bottle and per milliliter, not just per piece.
- THC content per dose, in milligrams. Hemp-derived does not mean THC-free.
- A batch COA with a full cannabinoid panel plus pesticides, heavy metals, and mold.
- Ratio direction. Some labels print CBD:THC, others print THC:CBD. Ask which way the store writes it.
- Whether the product in your hand is the same batch as the paperwork. Batch numbers should match.
Ratios don't replace a neurologist
CBD changes how the body clears clobazam and can nudge valproate levels. It can also raise liver enzymes, which is why the prescription version comes with liver monitoring. Start low, hold the dose for a couple of weeks, and keep a seizure diary with dates, times, and doses. Bring it to your neurologist. If you're on antiseizure medication, none of this should happen without them knowing.
What to expect at the store
Bring your ID, expect a wait, and ask for the COA before the sales pitch starts. In most states a budtender cannot give medical advice, so treat them as a label reader rather than a clinician. THC caps and allowed product types vary by state, so the 20:1 tincture you read about may not exist where you live. If it doesn't, a plain CBD isolate from a brand that publishes test results is a fine substitute.
This is product information, not medical advice. Seizures are a reason to have a doctor in the loop from day one.