Topic
7 research guides on t4+t3 combination therapy.
The four brands most often recommended when Cynomel or Cynoplus runs out are not interchangeable. Three are liothyronine-only, one is a T4+T3 combination at a different ratio, one has been discontinued in its home market, and one is sold in two strengths seven and a half times apart. Verified specifications, dose-unit arithmetic, and what a forced brand switch actually does.
The most repeated unanswered question in thyroid research forums is arithmetic: if a protocol runs 125 mcg of levothyroxine, how much T3 replaces part of it, and how much T4 comes out? This is the full conversion reference - every common levothyroxine strength, the substitution conventions in circulation, worked examples, and the reasons equal micrograms do not mean equal effect.
Combination thyroid tablets are built at roughly 4:1 or 5:1 T4 to T3 by weight, while a healthy thyroid secretes closer to 20:1. The gap is larger than it looks, because ratios quoted by weight and ratios quoted in molar terms are not the same number. A 4:1 weight ratio is about 3.35:1 molar, roughly five times more T3-weighted than the gland.
Splitting a combination tablet splits both hormones, but only one of them has anything to gain. Levothyroxine has a half-life of about a week and no meaningful serum peak to manage; liothyronine peaks within hours. This covers why researchers end up splitting combination tablets, what the practice actually achieves, the tablet-fragment accuracy problem, and the formats that remove the need entirely.
A slow-release combination product is not two extended-release hormones. Levothyroxine already produces a flat serum profile from once-daily dosing and has nothing to gain from extension. The entire difference between an immediate-release and a slow-release combination sits in the T3 component - and that specific formulation has become an active area of randomised research since 2023.
Cynomel has been intermittently unavailable for years and effectively absent since 2025, with the last widely reported lots carrying a September 2025 expiry. There has been no formal discontinuation notice. This is an assessment of what is actually documented versus what is forum inference, why pharmacy listings persist for products nobody can ship, and what the wider liothyronine supply picture looks like in 2026.
Cynoplus is a Laboratorios Grossman T4+T3 combination tablet sold in two strengths - 60/15 mcg and 120/30 mcg, 50 tablets per bottle. Supply through Mexican pharmacy channels has become unreliable. This guide covers what the 120/30 formulation actually contains, how the named alternatives (Tiromel, Triyotex, Novothyral, Tertroxin, NDT, separate T4 and T3) compare on ratio and formulation, and how to carry a Cynoplus dose across to a slow-release T4+T3 equivalent.