Open almost any supplement bottle and read the “other ingredients” line beneath the active dose. There's usually something there: a flow agent, a bulking agent, sometimes a colourant. None of it is illegal, and most of it is genuinely low-risk. The real question isn't whether it's allowed. It's whether it needs to be there at all, and what a brand chose instead when it decided it didn't.
What fillers actually do
Excipients, the catch-all term for anything in a capsule that isn't the active ingredient, exist to solve manufacturing problems. Silicon dioxide, permitted as an anti-caking and carrier agent in supplements, stops fine powder clumping as it moves through machinery. Magnesium stearate, a lubricant used across the pharmaceutical and supplement industry, reduces friction so capsules fill at speed without sticking to equipment. Bulking agents like maltodextrin or microcrystalline cellulose pad out a capsule when the active dose is small enough to rattle around inside an empty shell. Without something doing that job, capsule-to-capsule fill weight becomes noticeably inconsistent within the same batch.
That's a genuine engineering problem, not an invented one. The honest answer to “why do brands use fillers” is usually manufacturing efficiency and cost, not anything sinister. Which is exactly why leaving them out isn't free: it means slower filling lines, tighter batch-to-batch quality control, and a formulation that has to be standardised precisely enough that it doesn't need a bulking agent to sit properly in the capsule.
The one that's worth knowing about
Most excipients, including magnesium stearate, silicon dioxide, and microcrystalline cellulose, have been formally re-evaluated by European food safety regulators and found to raise no safety concern at the levels actually used. Titanium dioxide is the exception worth knowing about. It's a white colourant used to make capsules look more uniform, and the EU banned it as a food additive in 2022 after regulators couldn't rule out genotoxicity concerns in its nanoparticle form. In the UK, it's still legally permitted. That gap matters: a supplement can be fully compliant with UK law and still contain something the EU has decided not to allow in food. We don't use it, not because it's currently illegal here, but because “technically permitted” isn't the standard we're testing against.
What's actually in a RedGold88™ capsule
Every RedGold88™ capsule contains the standardised 50:1 saffron extract and a plant-based, vegan capsule shell. Nothing else. 0% fillers, additives, preservatives, or artificial colourings, which is a real formulation choice, not a label decision made after the fact. It's part of why the extract is standardised as precisely as it is: a capsule with nothing to bulk it out needs the active dose itself to be consistent, batch after batch, or the whole thing falls apart at the manufacturing stage.
Reserve Threads doesn't have this conversation to have in the first place. Whole saffron threads have nothing added and nothing to encapsulate, so the question of fillers simply doesn't arise, which is one of the quieter advantages of buying saffron as threads rather than as a processed ingredient.
What to check on any supplement label
Look past the active ingredient line to the “other ingredients” list beneath it. A short list with recognisable, functional ingredients is normal and not automatically a problem. What's worth questioning is a long list of bulking or flow agents that only exist to compensate for an inconsistent or very small active dose, or a colourant with no function beyond appearance. If a brand can't or won't explain why each ingredient beyond the active dose is there, that's usually because it wasn't a deliberate choice.
Two ways to buy saffron without the extras
If you're taking saffron for mood, calm, or sleep, RedGold88™ Extract gives you a standardised 50:1 dose in a capsule with nothing added beyond the extract itself and a vegan shell. If you're cooking, Reserve Threads is whole saffron with nothing to fill in the first place.