If you have built a protocol around Cynoplus and your usual supply channel has stopped delivering, the practical question is narrow and specific: what actually contains the same two hormones, in the same proportion, at a dose you can carry across without restarting your titration from zero?
Most of the answers circulating in bioenergetic and thyroid research forums do not survive scrutiny. The products most frequently named as Cynoplus alternatives - Tiromel, Triyotex, Cynomel - are T3-only preparations. Substituting any of them for a combination tablet does not replace Cynoplus; it removes the levothyroxine component entirely and leaves a researcher on T3 monotherapy without having decided to make that change.
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This guide covers what Cynoplus actually is at the formulation level, which of the named alternatives are genuinely comparable, and how the dose arithmetic works when moving between them. The broader history of Grossman's thyroid line, the counterfeit problem, and the Mexican export situation are covered separately in the Cynomel and Cynoplus sourcing analysis. This piece is about the replacement decision.
What Cynoplus Actually Contains
Cynoplus is a levothyroxine sodium plus liothyronine sodium combination tablet manufactured by Laboratorios Grossman in Mexico. It is registered in two strengths:
| Strength | Levothyroxine (T4) | Liothyronine (T3) | Ratio by weight | Presentation |
|---|---|---|---|---|
| Cynoplus 60/15 | 60 mcg | 15 mcg | 4:1 | 50 tablets |
| Cynoplus 120/30 | 120 mcg | 30 mcg | 4:1 | 50 tablets |
Both strengths hold the same 4:1 proportion. The 120/30 is the higher-dose presentation and is the one most commonly referenced in research-community discussion, largely because it corresponds to a full replacement-range T4 dose rather than a partial one.
This matters for substitution because the two numbers move together. A researcher who describes their protocol as "one Cynoplus daily" is describing two separate hormone doses at a fixed proportion, and any alternative has to be assessed on both.
Why 4:1 Is the Point
A healthy human thyroid secretes both hormones, but not in anything close to a 4:1 proportion. Daily gland output is dominated by T4, with T3 contributing a small direct fraction and the majority of circulating T3 arising from peripheral deiodination of T4 in liver, kidney and other tissues.
Every T4+T3 combination tablet therefore represents a deliberate departure from glandular proportions. The premise is that in some individuals the peripheral conversion step is the limiting factor, so supplying a larger share of the dose as pre-converted T3 bypasses a bottleneck that a T4-only preparation cannot address.
That premise has a genetic strand of support. Polymorphism in the DIO2 gene, which encodes type 2 iodothyronine deiodinase, has been associated with reduced deiodinase-2 activity and lower serum T3 in thyroid-deficient individuals. The mechanism of the conversion step itself is covered in the deiodinase dysfunction guide.
It also has a substantial clinical literature that remains genuinely unsettled. A consensus document on evidence-based use of levothyroxine and liothyronine combinations set out the state of the argument, and a 2026 network meta-analysis of additional treatment strategies for hypothyroidism revisited it. Both are listed in the sources below. Neither concludes that combination therapy is superior for unselected populations, and a 2025 multisource systematic review examined risk of death and adverse effects in patients on liothyronine. Anyone evaluating a combination protocol should read the counter-evidence as carefully as the supporting evidence.
What is not in dispute is the arithmetic. A 4:1 tablet delivers a far higher T3 fraction than the gland does, and that is the entire reason the format exists.
Why Cynoplus Supply Became Difficult
The supply picture has degraded on several fronts at once, and none of them are about demand.
Grossman's Mexican-market distribution was never designed around international research demand. Tightened export handling, unpredictable customs enforcement, and periodic manufacturing pauses have all been reported by researchers attempting to maintain continuity of supply. Forum threads tracking Cynomel production status have run for years and across many pages without resolution, and Cynoplus has been reported out of stock at Mexican pharmacy sites that previously carried it reliably. What is actually documented about that status, as against what is forum inference, is assessed in is Cynomel coming back.
The second problem is verification. When a product with an established following becomes scarce, material circulates that claims to be that product. Substandard and falsified medicines are a documented and systematically studied problem, and the qualitative evidence on their drivers in low and middle income supply chains is summarised in one of the sources below. For a thyroid hormone tablet, the practical consequence is that dose accuracy cannot be confirmed by inspection. A tablet that looks correct may contain a different quantity of either hormone, or neither. Without HPLC analysis there is no way for an end user to know.
That verification gap is the part of the problem that switching brands does not solve, because it applies to any product moving through the same informal channels.
Verifying What You Actually Received
Availability and authenticity are separate problems, and only one of them is solved by finding a new supplier.
A levothyroxine plus liothyronine tablet gives an end user almost nothing to inspect. Both hormones are active in microgram quantities, so a tablet containing half the stated dose, twice the stated dose, or only one of the two hormones is visually indistinguishable from a correct one. Colour, scoring, imprint and blister presentation are all reproducible. Packaging is the easiest part of a pharmaceutical product to imitate and the least informative about what is inside it.
This is not a concern peculiar to thyroid products. Substandard and falsified medicines are a systematically studied problem with a documented literature on their drivers and on the conditions under which they proliferate, summarised in one of the reviews cited below. The pattern that review describes is consistent: informal supply routes, scarcity of a sought-after product, and limited post-market surveillance are precisely the conditions under which unverifiable material enters circulation. Every one of those conditions currently applies to Cynoplus.
For a fixed-ratio thyroid tablet the consequences are specific and asymmetric. If the T3 content is wrong, the effect tends to appear quickly, within hours of dosing, because that is how immediate-release liothyronine behaves. If the T4 content is wrong, the effect appears slowly and diffusely across weeks, because T4 accumulates toward a new steady state rather than producing an acute signal. A researcher can therefore run an incorrect T4 dose for more than a month without any single day offering evidence of it.
The only reliable answer is analytical rather than observational. High-performance liquid chromatography can establish the actual content of each hormone in a given batch. That is a laboratory procedure, not something an individual can perform on a tablet, which is why batch-level verification has to be a property of the supply chain rather than a step the end user takes at the point of use.
The relevant question when evaluating any Cynoplus replacement is therefore not only what it contains on paper, but whether anyone has measured what is in the specific batch being supplied. A product sourced through the same informal channels that made Cynoplus unreliable inherits the same verification gap regardless of the name printed on the box.
The Named Alternatives, Assessed
Forum discussion consistently surfaces the same handful of products. They are not interchangeable, and the most important distinction is whether a given product contains T4 at all. Verified specifications for all four, including excipients and dose-unit arithmetic, are set out in the four-brand comparison.
Novothyral (100/20)
The closest branded analogue. Novothyral is a European-market levothyroxine plus liothyronine tablet at 100 mcg and 20 mcg, which is a 5:1 ratio rather than Cynoplus's 4:1. It is a genuine combination product and the substitution is conceptually straightforward, but the proportions are not identical: moving from Cynoplus 120/30 to Novothyral 100/20 reduces both hormones and shifts the ratio toward T4.
Tiromel, Triyotex, Cynomel, Tertroxin
All four are liothyronine-only. Tiromel is a Turkish-market 25 mcg liothyronine tablet, Tertroxin is a UK 20 mcg liothyronine tablet, Cynomel is Grossman's own 25 mcg T3 product, and Triyotex is likewise a T3 preparation. They are frequently recommended in the same forum threads as Cynoplus because they solve the T3 half of the problem, and because for a period they were easier to source.
None of them replaces Cynoplus. Using one as a substitute converts a combination protocol into a T3-only protocol, which is a materially different intervention with a different titration curve and a different side-effect profile. That may be a deliberate choice, and the T3-only versus combination comparison covers the trade-off, but it should be a decision rather than an accident of what happened to be in stock.
Desiccated thyroid (NDT)
Animal-derived desiccated thyroid contains T4 and T3 along with T2, T1 and calcitonin. It is a genuine combination preparation and has a long history of use. Its limitation for research purposes is standardisation: the ratio and total hormone content vary with the source material, which makes it difficult to hold a protocol variable constant across batches. This is compared in detail in the NDT versus slow-release T3 analysis.
Separate T4 and T3
Taking levothyroxine and liothyronine as two separate preparations is the most flexible option and the one most often recommended by clinicians, precisely because the ratio becomes adjustable rather than fixed. It reproduces any Cynoplus strength exactly, and it allows the two components to be titrated independently.
The costs are practical rather than pharmacological: two products to source instead of one, two dose calculations, and the loss of the fixed-ratio simplicity that made a combination tablet attractive in the first place.
The Formulation Problem Nobody Solves by Switching Brands
Every product listed above shares one characteristic with Cynoplus: the T3 component is immediate-release.
Liothyronine given as an immediate-release oral dose reaches peak serum concentration roughly 2 to 4 hours after administration, with a half-life in the region of a day for T3 but a much sharper early rise than T4 produces. In a combination tablet, the T4 component contributes a stable background because of its long half-life and large distribution pool, while the T3 component produces a distinct early peak followed by a decline.
This is the pharmacokinetic pattern behind the complaints that recur across combination-therapy discussion: an early surge in the hours after dosing, then a flatter or low period later in the day. It is a property of the formulation, not of the ratio, and it is why some researchers end up splitting a combination tablet into halves or quarters through the day - an approach that manages the peak but multiplies the dosing burden and works poorly with a tablet whose two hormones have very different kinetics.
Work on extended-absorption liothyronine formulations, including a phase 1 human study of poly-zinc-liothyronine and translational work on sustained release T3 therapy, has targeted exactly this problem: keeping total T3 exposure comparable while flattening the early peak. Both papers are cited in the sources below.
A slow-release T4+T3 formulation applies the same HPMC matrix approach used in sustained-release T3 to the combination format, holding the 4:1 ratio while extending the T3 release window. The SRT4+T3-120 slow release T4+T3 is formulated at 120 mcg T4 and 30 mcg T3, matching the Cynoplus 120/30 strength and presentation while changing the release profile of the T3 component.
The Half-Life Asymmetry Nobody Mentions
The two hormones in a combination tablet do not operate on the same timescale, and this is the most under-discussed complication when switching between combination products.
Levothyroxine has a long elimination half-life, conventionally given as about a week. Liothyronine's is considerably shorter, on the order of a day. That difference produces a consequence that matters during any switch: after a change to a combination dose, the T3 side re-equilibrates within a few days, while the T4 side takes roughly four to six weeks to reach a new steady state.
A researcher changing combination products therefore experiences the two halves of that single change at completely different speeds. Whatever the T3 component is going to do, it does almost immediately. Whatever the T4 component is going to do, it does slowly, and its full effect is not visible until well over a month has passed.
Two practical errors follow from ignoring this.
The first is attributing an early change to the wrong hormone. Anything observed in the first week after a switch is far more likely to reflect the T3 component, or a change in its release profile, than the T4 component, which has barely begun to move. Adjusting the T4 dose in response to a first-week observation is adjusting the variable that has not yet expressed itself.
The second is assessing a switch too early. Bloodwork drawn two weeks after a change captures a settled T3 picture against a T4 level still in transit. That is not a steady-state result and it cannot be compared cleanly against pre-switch values. This is the standard reason combination-therapy assessments are conventionally deferred to around the six-week mark.
The asymmetry also explains why the fixed ratio of a combination tablet is a convenience rather than a physiological necessity. The ratio governs what goes in on a given day. It does not govern what circulates, because the two hormones accumulate and clear on entirely different schedules.
Matching a Cynoplus Dose
The useful property of a fixed-ratio tablet is that dose-matching is arithmetic rather than judgement, provided the ratio is preserved.
| Current Cynoplus protocol | Total daily T4 | Total daily T3 | Equivalent at 4:1 |
|---|---|---|---|
| Half of 60/15 | 30 mcg | 7.5 mcg | Quarter of a 120/30 |
| One 60/15 | 60 mcg | 15 mcg | Half of a 120/30 |
| One and a half 60/15 | 90 mcg | 22.5 mcg | Three quarters of a 120/30 |
| One 120/30 | 120 mcg | 30 mcg | One 120/30 |
| Two 60/15 | 120 mcg | 30 mcg | One 120/30 |
| One 120/30 plus one 60/15 | 180 mcg | 45 mcg | One and a half 120/30 |
Two cautions apply to reading that table.
First, it holds only while the ratio is held. Moving to Novothyral at 5:1, to NDT, or to separate preparations means the two hormones no longer scale together and each has to be calculated on its own.
Second, equal milligrams do not guarantee equal serum behaviour. Changing the release profile of the T3 component changes the shape of the curve even when total daily exposure is matched, which is the entire point of the change but also means the first weeks on a new formulation are not directly comparable to the last weeks on the old one. The slow-release T3 titration guide covers how that transition is normally approached, and the T3 conversion calculator handles the arithmetic for mixed protocols.
For researchers who prefer to run the two hormones separately rather than in a fixed ratio, T4 levothyroxine at 100 mcg and the slow-release T3 range allow any proportion to be constructed.
What the Transition Period Actually Involves
Given the half-life asymmetry, a switch between combination products has a predictable shape even where the individual response does not.
The first few days are dominated by the T3 component. If the release profile has changed, this is when the difference is most apparent, because an extended-release formulation removes the early peak that an immediate-release tablet produces. Researchers moving from immediate-release to extended-release frequently describe the first week as feeling flatter. That is the intended pharmacokinetic consequence rather than evidence of underdosing: total daily exposure has not fallen, its distribution across the day has changed.
Weeks two and three are the least informative stretch of the entire transition. The T3 side has settled, the T4 side is still moving toward its new level, and any measurement taken here reflects a mixture of one settled variable and one in transit. Decisions made in this window are being made on incomplete information.
By weeks four to six the T4 component is at or near its new steady state and the picture becomes interpretable. This is the first point at which a comparison against pre-switch values means anything, and the first point at which a dose adjustment has a defensible basis.
Holding the dose constant across that window is what makes the comparison possible at all. Every mid-transition adjustment resets the T4 clock and pushes the earliest interpretable assessment further out, which is why a switch adjusted three times in six weeks yields far less usable information than one left alone. The same logic underlies the approach described in the slow-release T3 starting dose guide.
What the Evidence Establishes, and What It Does Not
Established. Cynoplus exists in two registered strengths at a 4:1 ratio. Immediate-release liothyronine produces an early serum peak that extended-release formulations are specifically designed to attenuate. DIO2 polymorphism is associated with reduced deiodinase-2 activity and lower serum T3 in thyroid-deficient individuals. Substandard and falsified medicines are a documented problem in informal supply chains.
Contested. Whether T4 plus T3 combination therapy outperforms levothyroxine monotherapy remains unresolved across the clinical literature. The consensus document and the 2026 network meta-analysis cited below both treat it as an open question rather than a settled one, and the 2025 systematic review on liothyronine safety exists precisely because the risk side is also unresolved.
Not established. That any particular ratio is optimal. That matching a milligram dose across formulations produces equivalent physiological effect. That a slow-release profile produces better outcomes rather than simply a different serum curve. The pharmacokinetic difference is measurable; the outcome difference is a hypothesis.
Frequently Asked Questions
What strengths does Cynoplus come in?
Two: 60 mcg levothyroxine with 15 mcg liothyronine, and 120 mcg levothyroxine with 30 mcg liothyronine. Both are 4:1 by weight and both are supplied as 50 tablets per bottle.
Is Tiromel a Cynoplus alternative?
No. Tiromel is a liothyronine-only tablet, typically 25 mcg. It contains no levothyroxine, so it replaces only the T3 portion of a Cynoplus dose. The same applies to Triyotex, Cynomel and Tertroxin.
What is the closest branded equivalent to Cynoplus 120/30?
Novothyral at 100/20 is the closest branded combination product, though it is a 5:1 ratio rather than 4:1 and delivers less of both hormones per tablet. A slow-release T4+T3 formulated at 120/30 matches the strength and ratio directly while differing in release profile.
Why is Cynoplus hard to get?
A combination of tightened Mexican export handling, inconsistent customs enforcement, reported manufacturing pauses, and distribution that was never structured around international demand. Scarcity has also drawn in unverifiable product, which is a separate and more serious problem than availability alone.
Can I just take levothyroxine and liothyronine separately?
Yes, and it is the most flexible approach because the ratio becomes adjustable. The trade-off is two products to source and two dose calculations instead of one fixed-ratio tablet.
Does a slow-release combination change my dose?
Not the milligram arithmetic, if the ratio is held. It changes the serum curve of the T3 component, which is the reason for the change but also means the transition period is not directly comparable to the previous formulation.
Is NDT the same as a T4+T3 combination tablet?
Both contain T4 and T3, but desiccated thyroid is animal-derived and also contains T2, T1 and calcitonin, with batch-to-batch variability in ratio and total content. A synthetic combination tablet holds the proportion constant.
How long before I can judge a new combination product?
Around six weeks. The T3 component settles within days, but levothyroxine takes roughly four to six weeks to reach a new steady state, so anything measured before then reflects a T4 level still in transit.
Why does the first week on a slow-release combination feel flatter?
Because the early serum peak produced by immediate-release liothyronine has been removed. Total daily T3 exposure is unchanged; it is spread across a longer window rather than concentrated into the hours after dosing.
How do I convert a Cynoplus dose if I switch to a different ratio?
Calculate the two hormones separately. Take your total daily T4 and total daily T3 from your current tablet count, then work out what combination of the new product delivers each. Once the ratio changes, the single-number shorthand stops working.
Closing Note
The Cynoplus supply problem is really two problems wearing one label. Availability is the visible one and it fluctuates. Verification is the durable one, and it does not improve by switching to whichever brand is currently in stock through the same channels.
For researchers whose protocols were built on the 120/30 strength, the substitution question comes down to whether the fixed 4:1 ratio is worth preserving. If it is, the options are a genuine combination product at a matched ratio or two separate preparations dosed to the same totals. If it is not, the far wider T3-only and NDT literature opens up, and that is a different decision requiring a different analysis.
What does not work is treating a liothyronine-only tablet as a drop-in replacement for a combination tablet, which is the single most common error in forum sourcing advice.
All compounds discussed here are research chemicals supplied for laboratory research use only. Nothing in this article is medical advice, a treatment protocol, or a recommendation for human or animal consumption. Thyroid hormone dosing carries genuine cardiovascular risk and the clinical evidence on combination therapy remains actively contested. Researchers should consult the primary literature cited below and appropriate qualified professionals.