Short answer: Sublingual and fast-dissolving tablets replace part of the standard filler system with a superdisintegrant — commonly croscarmellose sodium — paired with a diluent like mannitol that dissolves readily instead of resisting breakup, and are pressed at a softer target hardness so they break apart quickly rather than holding together like a standard tablet. Chewable tablets use a similar softer-hardness approach but prioritize flavor and texture over disintegration speed, typically built around mannitol or other sugar alcohols for a pleasant, non-gritty bite. Both are meaningfully different formulations from a standard direct-compression tablet, not just a tweak to the standard recipe.
If you've formulated a standard direct-compression tablet before, the underlying process is familiar — what changes is the excipient system and what you're optimizing for at the press.
What Makes Sublingual and Fast-Dissolving Tablets Different
A standard tablet is formulated to hold together — a binder-heavy excipient system and enough compression force to keep it solid through handling and shipping. A sublingual or fast-dissolving tablet needs the opposite outcome once it reaches the mouth: it needs to break apart quickly, ideally in well under a minute, rather than hold together at all. That means swapping part of the standard binder/diluent system for ingredients chosen specifically to promote rapid disintegration instead of resisting it.
Formulating for Fast Disintegration
The core addition is a superdisintegrant — croscarmellose sodium is the standard choice — which swells rapidly on contact with moisture and physically breaks the tablet apart from within. This is typically paired with a diluent like mannitol, which dissolves readily rather than resisting breakup the way a diluent chosen for a standard tablet would. ReadyBlend Fast-Disintegrating is built on exactly this combination — microcrystalline cellulose, mannitol, croscarmellose sodium, magnesium stearate, and silicon dioxide — formulated for disintegration typically under 60 seconds, if you'd rather start from a validated blend than build the ratio from scratch. If you are building your own, how to make a direct-compression powder covers the standard four-role framework this modifies.
Compression Force and Hardness Targets
Fast-dissolving tablets are generally pressed at a softer target hardness than a standard tablet — enough force to hold together through handling and packaging, but not so much that it works against the superdisintegrant's ability to break the tablet apart quickly. This is one case where the usual instinct to press harder for a sturdier tablet actively works against the goal. See testing tablet hardness and friability for how to measure where your batch actually lands, and expect to test disintegration time directly (see below) rather than relying on hardness alone as a proxy.
Chewable Tablet Considerations
Chewable tablets aren't optimized for rapid disintegration the way a sublingual tablet is — they're formulated to be chewed, so texture and flavor matter more than break-apart speed. Mannitol and other sugar alcohols are common base ingredients here too, chosen for a smooth, non-gritty mouthfeel and pleasant sweetness rather than for disintegration performance specifically. Chewables are typically pressed softer than a standard swallowed tablet as well, since a tablet that's too hard to comfortably chew defeats the format's purpose regardless of how it's formulated otherwise.