Should I be on T4 only, or do I need T3 too?

No, not everyone with Hashimoto’s and hypothyroidism needs T3 in addition to T4—but many women feel dramatically better when they do, especially once root causes are addressed.

From a functional medicine or holistic lens, the goal isn’t just normalizing TSH on your labs. It’s restoring energy, mood, metabolism, brain function, and overall vitality by supporting your body’s natural hormone production and conversion while healing the underlying drivers of autoimmunity and poor thyroid performance.

Why T4-Only Meds like Levothyroxine Are the Default—but Often Falls Short in Hashimoto’s

Conventional medicine starts (and usually stays) with synthetic T4 (levothyroxine/Synthroid/etc.) because your thyroid normally makes mostly T4, which your body converts to active T3. This is the hormone that actually powers your cells. The assumption is “your body will handle the rest.”

In Hashimoto’s, that conversion frequently breaks down. Chronic inflammation from the autoimmune attack, plus common co-factors like stress, gut issues, and nutrient deficiencies, down-regulates the enzymes (deiodinases) that turn T4 → T3. That means the enzymes don’t work as well.

The result?

You can have “normal” TSH and free T4 while your free T3 is low and reverse T3 (the inactive “brake”) is high—leaving you with fatigue, brain fog, depression, weight gain, cold hands/feet, hair loss, and other symptoms that T4 alone never fully fixes.

I see this pattern a lot. Many clients report they only started feeling like themselves again after adding T3 or switching to natural desiccated thyroid (NDT/Armour, Nature-Throid, etc.), which contains both T4 and T3 in a ratio closer to what a healthy thyroid produces (roughly 4:1 or 80/20).

Surveys of thousands of Hashimoto’s patients show ~60% feel better on T4+T3 or NDT versus T4-only.

The Root Cause Priority: Fix Conversion First, Then Decide on Medication

Instead of jumping straight to “add T3,” a holistic approach asks: Why is conversion impaired? Address these root drivers and you often need less medication—or a lower dose of T3—while feeling dramatically better.

Common conversion blockers in Hashimoto’s (and how to support them):

Nutrient deficiencies — Selenium, zinc, iron/ferritin, and vitamin A are required for the conversion enzymes. Low ferritin (<50–70 ng/mL) is especially common in women and tanks T4 → T3.

Gut dysfunction — 20% of conversion happens in the intestines. Leaky gut, dysbiosis, or inflammation (very common in Hashimoto’s) blocks it. Many women improve conversion simply by going gluten- and dairy-free and healing the gut through an anti-inflammatory diet and possibly some supplementation. When you have Hashimoto’s, you likely need regular gut healing rather than just a one time protocol. Gut healing includes removing things that are negatively affecting your gut whether it is infections, foods, etc. Then you need to make sure you are digesting food well. You might need some prebiotics or a specific probiotic for gut healing. Then you need to give your gut nutrients it needs to heal.

Chronic stress/high cortisol — This shunts T4 into reverse T3 instead of active T3. In this case Adrenal support, meditation, yoga, or ashwagandha can literally raise free T3. Ashwagandha will improve T4 to T3 conversion so you need to be really careful with it. Adrenal support can include managing stress and ensuring good sleep but you may also need to do something like a pinch of salt in your water or maybe you need licorice root. Reading a simple CBC - looking at sodium and potassium can tell us if you have issues with cortisol.

Liver sluggishness — Most conversion occurs here so if the liver is congested this won’t happen. This idea of sluggish liver is talked about in whole person care or holistic care and it just means your liver isn’t operating at its peak even when your labs might say your liver is fine. The lab ranges I go by are much smaller so I might pick up something that is off sooner than your doctor.

It’s common for women with Hashimoto’s and hypothyroidism to have issues here because the thyroid depends heavily on the liver and hypothyroidism slows down liver function, creating a vicious cycle.

Most of the conversion of T4 to T3 happens in the liver and T3 is actually what makes your metabolism run. More conversion happens in the gut- so if you have a messed up gut and a liver that is sluggish- you have got some issues.

In addition, the liver clears out thyroid hormone and excess estrogen. If the liver isn’t doing that, you get excess estrogen which causes free thyroid hormones to get bound up so they don’t reach your cells. You can have normal TSH and normal Free T4 on labs - often all that is checked by your doctor and you will still have hypothyroid symptoms.

Hypothyroidism also slows the production of bile and makes your gallbladder sluggish- clogging the liver detox pathways. You can end up with a fatty, inflamed, or congested liver and have less T4 to T3 conversion.

Add a high refined carb diet to the mix, environmental toxins, chronic stress, estrogen dominance, and nutrient deficiencies. What do you think is going to happen?

Signs your liver might be sluggish:

• bloating after eating fatty meals. constipation, pale stools, floating stools

• stubborn weight gain, belly fat, high cholesterol/triglycerides

• acne, eczema, psoriasis, rashes, itchy skin, heavy/clotted periods

• chemical sensitivity, bad breath, easy bruising, headaches

• fatigue, brain fog, depression, feeling toxic.

I do not believe in aggressive detox protocols. It’s dangerous and can displace toxins to other areas of the body leading to more problems. An aggressive detox program can also make hashimoto’s flare.

Gentle liver support would include eating lots of liver loving foods. Bitter, fiber rich foods. Dandelion greens, arugula, radicchio, artichoke, beets, carrots, cruciferous veggies, garlic, onions, turmeric, berries, dark leafy greens. Aim for 30 or more grams of fiber per day. Reduce sugar, refined carbs, alcohol, processed foods.

Milk thistle tea protects liver cells. You might need some bile support too. Just depends.

Inflammation from Hashimoto’s itself — Think of inflammation in the body- the kind you can’t see or feel necessarily as your body being mad and not telling you- all the while it is just stewing about something creating damage unknown to you.

It is one of the biggest things that can sabotage your ability to get well. It’s attacking your thyroid gland, it disrupts how your body uses thyroid hormone at the cell too. This is why many of you feel terrible when your TSH is normal and your on T4 only meds. At the core, inflammation is interfering with the T4 to T3 conversion and promotes the conversion to reverse T3 which is the body’s way of trying to protect you and you end up with hypo symptoms.

You get in this vicious cycle where inflammation is causing more inflammation. Having low T3 levels worsen inflammation because thyroid hormones naturally stop the damage.

Lowering antibodies through diet, LDN (low-dose naltrexone), or treating triggers (infections, toxins, stress) improves conversion naturally.

Other factors — things that don’t show up on standard labs but they keep your body feeling hypothyroid even when your medication dose looks perfect.

Low calorie dieting or chronic under eating- We are wired for survival so when calories drop below what you need- less than 1,800-2,000 for most women, maybe more if you are really active or an athlete. When we don’t eat enough our body thinks ‘famine’ and conversion of T4 to T3 stops, you get more reverse T3 to conserve energy. Your body literally slows you down thinking you are in a state of famine. This causes more inflammation too. If you have plateaued at weight loss despite the perfect diet, you feel cold, you are losing hair, your period is off, you have extreme fatigue after meals, or labs show low T3, even within the range you may not be eating enough.

Make sure you are getting enough protein- a good start is one gram protein per one pound of body weight. That’s a pretty general recommendation but still a very good place to start. If this seems overwhelming,  start with breakfast and then lunch and then dinner. Remember a palm size of meat is about 25-30g of protein. You can get it in if you are intentional about it.

Stop restricting so many foods. If you are sensitive to a lot of foods, you probably have leaky gut and rather than avoiding 25 foods, you need to bring down inflammation and heal your gut.

Heavy Metals and Environmental Toxins

Mercury from dental fillings, fish and even vaccines can be triggers along with lead, cadmium, arsenic, and fluoride. These bind selenium making it unavailable to convert T4 to T3. They create oxidative stress which is like rust on your cells and this damages liver and thyroid cells. It can make autoimmune attacks worse, especially mercury with TPO.

These things accumulate in the body because of sluggish detox pathways and an inflamed thyroid so the body can’t clear them. This is also one big reason why you should not start with a detox. If you can’t clear these and you do a calorie deficit detox you are risking making yourself worse.

If you are on any of the following medications, they interfere with thyroid conversion or the message coming from the brain.

• Beta blockers block conversion from T4 to T3

• Steroids suppress conversion

• Lithium, SSRIs, anticonvulsants, and high dose biotin can interrupt thyroid function

• Birth control pills or HRT raise thyroid binding globulin, lowering the amount of hormone that gets to your cells and can also worsen estrogen dominance that burdens the liver.

Some people have a genetic polymorphism to the gene that codes for the enzymes that convert T4 to T3 inside the cells making the process less efficient. If you are doing everything right and your labs still show T4 is fine but T3 is low, or you have normal TSH and Free T4 but you have massive brain fog, depression, fatigue, and poor response to T4 only meds this might be an issue for you. This issue can make you more sensitive to inflammation.

These things rarely exist in isolation but you are likely dealing with many of these factors which is why we have to peel back layers of the onion so to speak. Fix one issue and then work on the next until all things are resolved and you are feeling better.

Here is what I recommend:

• Comprehensive labs (not just TSH): free T3, free T4, reverse T3, TPO/TG antibodies, ferritin, vitamin D, selenium, zinc, B12, and a full gut/inflammation panel.

• Anti-inflammatory, nutrient-dense diet (gluten-free and often dairy-free for 3–6 months is a game-changer for many).

• Targeted supplements specific to what your body needs.

• Stress and sleep optimization.

• Gut healing protocol.

• Once these are in place, retest. If free T3 is still low, reverse T3 high, or symptoms linger despite optimal labs, that’s when adding T3 becomes logical.

Medication Options Through a Functional Lens

T4-only — Works beautifully for some women once root causes are fixed. Clean versions like Tirosint (gel cap or liquid) avoid fillers that can trigger Hashimoto’s.

T4 + T3 combo — Synthetic (levothyroxine + liothyronine/Cytomel) or compounded. Allows precise dosing. Many start low (e.g., 5–10 mcg T3) and titrate based on symptoms and labs.

Natural desiccated thyroid (NDT) — Contains T4, T3, and trace T1/T2. Often preferred because it mimics human thyroid tissue more closely. Some women swear by it for energy and weight loss; others do better on synthetic combo if they react to the porcine proteins.

The evidence is mixed in large studies (some show no average benefit, others show patients with persistent symptoms or Hashimoto’s specifically prefer and do better on T3-containing therapies). I honor your individual response: if you feel better and labs improve, that’s what matters. Roughly half of patients in preference studies choose combo therapy over T4-only.

Bottom Line

You don’t have to be on T3, but you also don’t have to suffer on T4-only if your body isn’t converting it well. I look at your full story—labs, symptoms, diet, stress, gut health, and life circumstances—and partner with you to find the right balance. Many women end up on a lower total dose of thyroid hormone (or even reduce medication over time) once the root causes are found and dealt with.