Natural Desiccated Thyroid vs Synthroid: Detailed Comparison, Brands, T3/T4 Ratios, and Conversion Tips

How Natural Desiccated Thyroid and Synthroid Really Work

Let’s cut straight to the science, because that’s where most of the confusion starts. Natural Desiccated Thyroid (NDT) and Synthroid (levothyroxine) both treat hypothyroidism, but they’re not built the same. NDT comes from the dried thyroid glands—usually pork—so it’s considered “natural.” Synthroid is fully synthetic, a man-made version of T4, the storage thyroid hormone most healthy bodies produce. The kicker? Your body still needs to convert T4 into T3, the active hormone that actually fires up cells and organs. NDT brings both T4 and T3 to the table, plus little bits of T1 and T2 you don’t find in most synthetic meds.

People with genetic quirks or conversion issues sometimes don’t do well on T4 alone. About 15% of thyroid patients still feel lousy on Synthroid, even when their labs look great. Ever wonder why? It’s likely because they can’t convert enough T4 to T3. Enter NDT: It’s got a fixed mix of both T3 and T4 that mimics the ratios found in a normal animal thyroid gland. But without strict standardization, these ratios can bounce around batch-to-batch. If you’re the kind of person who’s really sensitive to hormone swings, this can mean unpredictable symptoms—one week you’re energetic, the next you’re anxious or exhausted.

Synthroid wins on consistency and dosing control—what’s in your tablet is always the same. That’s why most mainstream endocrinologists recommend starting with it. The flip side? Some folks miss the “real” T3 and feel stuck in low gear. If you ever see someone fiercely loyal to their Armour or Nature-Throid, this is probably why. Being able to get a little T3, even if it’s tiny, sometimes smooths out brain fog, sluggishness, and stubborn weight gain.

Not all that’s natural is better, of course. NDT carries the risk of unpredictable absorption if you have GI issues, and those allergic to pork can’t use it. On Synthroid, too little or too much can sneak up on you—it always takes a few weeks for side effects to show up. If you have a history of arrhythmia, careful monitoring is key, since T3 boosts your heart rate even more than T4.

So if you’re chasing better symptom relief, NDT gives you T3 upfront. Want exact dosing, less chance of hormone swings, and easier lab tracking? Synthroid is built for that. The “natural vs synthetic” debate is really about what your individual body can use best. Keep that front and center as you learn more about NDT brands and dosing below.

NDT Brands: The Landscape, Differences, and What to Watch Out For

You walk into a pharmacy looking for NDT, and suddenly the shelves show Armour Thyroid, NP Thyroid, Nature-Throid—even Canadian brands like Erfa. Here’s where things get interesting. All NDTs use animal thyroid, but the devil’s in the details: binders, fillers, and how strictly companies test their hormone doses.

Armour Thyroid is the best-known, dating back to the 1930s. It’s reliable in hormone content by modern standards, but it uses lactose as a filler—bad news if you’re lactose intolerant. NP Thyroid was the hero for patients a few years ago, but a reformulation in 2018 set off a wave of reports: people complained of worsened hair loss, new fatigue, and even weird odors and taste. The company tweaked the formula, but many never felt the same on it. Nature-Throid and WP Thyroid (made by RLC Labs) prided themselves on having fewer fillers and being hypoallergenic, but supply issues and recalls have plagued these brands since 2019. Some patients describe Nature-Throid as “smoother” and easier on their digestion when it’s available—but there’s no guarantee your pharmacy will have it.

If you’re outside the US, you may come across Erfa Thyroid in Canada. This one has a unique texture—almost powdery—and some users swear it absorbs faster. Yet, others say it doesn’t keep symptoms at bay as consistently as Armour. For vegans or those with extreme sensitivities to pork, compounded NDT (where a pharmacist custom-makes your dose) offers a last resort, but expect to pay more and work closely with your doctor to dial in the right dose.

Feeling whiplash from all the brands? Consider this: pharmacies may switch brands without warning due to insurance changes or backorders. That means you could get Armour one refill and NP the next, which can be a nightmare if you’re dose-sensitive. Whenever you get a refill, check the label and pill appearance—don’t just assume nothing has changed. If you notice a sudden return of symptoms or weird side effects after a pharmacy switch, demand the same brand as last time or ask your doctor to put “no substitutions” on the prescription.

Here’s a look at key differences between popular NDT brands:

If you’re stuck between brands, talk to your doctor about trying a lower dose or splitting your tablet to see which changes actually move the needle for your symptoms. Some users crush and dissolve NDT in water to help absorption, but check with your pharmacist before trying this.

Breaking Down T3/T4 Ratios: Why Does It Matter?

If you’ve heard internet chatter that “NDT has the perfect thyroid hormone mix,” here’s what’s really going on. NDT contains both T4 (thyroxine) and T3 (liothyronine) in about a 4:1 ratio. A standard 60 mg (= 1 grain) NDT pill has around 38 mcg T4 and 9 mcg T3. Compare that to what a healthy human thyroid cranks out: most people make about a 14:1 ratio, with roughly 100 mcg of T4 and 6 mcg of T3 daily. That means NDT actually gives you relatively more T3 than your body would on its own.

Why does this matter? T3 is extremely potent—about four times stronger than T4. So what looks like a “balanced” dose on paper can punch much harder, especially if you’re sensitive to T3. You might feel heart palpitations, shaky hands, anxiety, or even rapid weight loss. At the same time, that higher T3 can snap people out of the sluggishness and brain fog that sometimes linger on T4-only treatment like Synthroid.

Endocrinologists tend to be conservative with T3 for good reason. It ramps up your metabolism—awesome if you want energy, less great if you accidentally tip into hyperthyroid territory. NDT has a risk of pushing your TSH (thyroid-stimulating hormone) to super low levels, which can stress your heart and bones over time. Chasing symptom relief by raising your NDT dose without doctor guidance is playing with fire.

Some online calculators claim they can convert your T4 dose to the “equivalent” NDT amount. These usually underestimate the T3 potency. If you’re considering a switch, a common way to avoid overdoing it is starting NDT at a lower dose and working up slowly over a few weeks.

Want to go deeper? Ask your doctor to check not only TSH, but also free T3 and T4 levels, and see where your numbers land during your best-feeling days. Don’t just chase numbers—some people run well with lower free T4 and higher T3, and vice versa. Symptoms trump labs every time, but both point the way. If you’re not getting anywhere with Synthroid, you can check some other alternatives to synthroid that mix T4 and T3 in different ways. Just don’t experiment without expert guidance.

NDT Conversion Dosing: Myths, Math, and Making the Switch

Lots of people wonder: If I’m on 100 mcg Synthroid, do I just swap for a certain grain count of NDT? It’s not that simple. Standard conversion charts suggest 100 mcg of levothyroxine (Synthroid) equals about 1.5 grains (90 mg) of NDT. But that ignores how punchy T3 is in the real world. In practice, safe conversion usually means starting 20% lower than the chart says, then moving up if needed after a few weeks of labs and symptom checks.

If you’ve been on Synthroid for years, your body’s used to stable T4 and slow conversion to T3. Suddenly dropping in a larger T3 dose—what NDT provides—can make things feel fast-forwarded. Some report a surge of energy, new anxiety, even increased hunger in the first week. That’s your tissues adjusting to higher circulating T3. The best tip? Start low, go slow. If your doctor isn’t familiar with NDT, print out the FDA’s package insert showing the hormone amounts per grain, and discuss every step in plain English.

Splitting your NDT dose—half in the morning, half mid-afternoon—spreads out the T3 “hit” and can lessen side effects like racing heart or insomnia. Some people get best results with three smaller doses a day (for the hardcore planners out there). Remember, T3 peaks within hours, and if you take all of it at breakfast, you might be wired but crash hard by dinner.

Lab checks are important. Check your TSH, free T3, and free T4 about 4-6 weeks after any dose change. Watch how your body feels: is your energy steady, is your hair thickness improving, have your bowels or mood shifted? Don’t just let your endo chase a "perfect TSH"—your best dose may not line up with textbook normal.

Be prepared for some trial and error. NDT converts differently across brands, and your gut absorption plays a big part. Digestive issues can block how much hormone gets through. Some even find crushing the tablet helps, while others need a totally different approach (like compounded formulas).

Switching to NDT isn’t a magic fix for every hypothyroid patient, but for those who struggle on Synthroid alone, adjusting the T3/T4 balance—carefully—has made a world of difference. Just don’t ditch your old prescription in one fell swoop. Wean off, monitor closely, and expect a few bumps before things level out.

The Real-Life Pros and Cons: What No One Tells You Upfront

On paper, NDT looks like the “natural” win: it’s been used for a century, it offers both T4 and T3, and it’s relatively inexpensive. But the everyday experience can be less black-and-white. One big perk? People often report clearer thinking and more natural energy, especially if they felt “off” on Synthroid despite good labs. For some, NDT perks up hair, skin, and digestive speed in ways T4 alone just doesn’t. Bonus: there’s less guesswork about getting any T3—NDT gives it to you outright.

But here’s what often gets glossed over: NDT’s T3 content is fixed and can’t be finely tuned without jumping up to the next grain size, which is a big leap. If your body needs just a tweak more or less T3, it’s a headache. Batch variability happens—one month’s refill might hit you just right, the next throws your sleep or mood into chaos. And with pork as the base, vegetarians, vegans, and folks with religious dietary restrictions are out of luck.

Synthroid shines on predictability. Every blue or pink tablet is atomically pure, so smart dosing adjustments are simple. Your endocrinologist is more likely to get behind it, your insurance covers it, and following lab numbers is a breeze. If you like to know exactly what you’re putting in your body, there’s no contest.

Downside? Sometimes T4-only just isn’t enough. If you can’t convert T4 well, no fancy labs or precise dosing will really fix your symptoms. Some roll the dice on adding a bit of liothyronine (synthetic T3) to their Synthroid just to edge closer to how NDT works, but this approach requires extra vigilance—and not every doctor is comfortable going off-label.

For those with heart rhythm problems or osteoporosis risks, T3 can increase those dangers. NDT is not recommended in pregnancy—switch to Synthroid if you’re expecting, since its dosing is far more reliable for mother and baby. And there’s always the logistical headache: NDT is sometimes in short supply, and insurance fights are common.

Bottom line? No one-size-fits-all answer is coming around the corner. If you’re not thriving on Synthroid, chatting with your health team about NDT or even the many alternatives to synthroid gives you more power to pick what’s right for your body and life. Track your symptoms, insist on regular labs, and take notes on each brand you try. The more details you give your provider, the faster you’ll get to real answers—because when it comes to thyroid, you’re truly your own best detective.