Q: Is a startle reflex as I'm falling asleep a side effect of Thyroxin, and is it anything to worry about?
A: Startle reflexes aren't known as a possible adverse effect associated with Thyroxin (Synthroid). It is normal for people to notice muscle jerking when they first fall asleep. This type of twitch or jerk can often be seen in people with irregular sleep schedules. The exact cause of twitches or jerks before sleep isn't fully understood, though one theory is that the jerks are part of a natural transition as your heartbeat and breathing slow down. Another theory is that as you fall asleep, your muscles relax and stop working, which could cause the brain to feel that you are falling through the air, resulting in the jerking or twitching. For more specific information about your own condition, consult with your doctor. Jennyfer Marsico, RPh
Immediate action required: Call 999 or go to A&E if:
- you get a skin rash that may include itchy, red, swollen, blistered or peeling skin
- you're wheezing
- you get tightness in the chest or throat
- you have trouble breathing or talking
- your mouth, face, lips, tongue or throat start swelling
You could be having a serious allergic reaction and may need immediate treatment in hospital.
These are not all the side effects of Thyroxin. For a full list see the leaflet inside your medicines packet.
You can report any suspected side effect to the UK safety scheme.
Mechanism of Action
Thyroxin (T4) is a synthetic version of one of the body’s natural thyroid hormones: thyroxine (T4). Normally, the hypothalamus secretes thyrotropin-releasing hormone (TRH), which then stimulates the anterior pituitary to secrete thyroid-stimulating hormone (TSH), which subsequently stimulates the thyroid to secrete 80% thyroxine (T4) and 20% L-triiodothyronine (T3). 50% of thyroxine (T4) then gets converted to its active metabolite L-triiodothyronine (T3). The thyroid hormones then work by binding to thyroid receptor proteins contained within the cell nucleus.
Once inside the nucleus, thyroid hormones work by directly influencing DNA transcription to increase body metabolism by increasing gluconeogenesis, protein synthesis, the mobilization of glycogen stores and other more functions.
In scenarios where this process is interrupted (as seen in primary, secondary, or tertiary hypothyroidism), Thyroxin (LT4) can mimic the body’s endogenous T4 production by the thyroid.
Q: What would happen if I do not take my Thyroxin? Is it dangerous to my health?
A: If you stop taking your thyroid hormone, Thyroxin, your body will return to symptoms of having a low thyroid, such as gaining weight, getting cold easily, depression, and having no energy. If you are out of refills from your pharmacy, you can legally ask for a three day supply while you are waiting to hear back from your doctor. Doctors usually ask for 48 to 72 hours to get a new prescription called in to the pharmacy. If your doctor is needing to see you for labs or just in general to see how the medication is working, you should contact them and tell them if there is a reason why you cannot get in. If they didn't have time to get you in before you run out, they will often give you a prescription to last until the appointment if you explain it to them. After all, they need to see how you are functioning on the medication at the dose they have prescribed. It does them no good to see how you are feeling when you are not on the medication. The same is true for labs. If you go in for a lab after stopping the medication, it will not be accurate, and the doctor is not usually looking for this reading. In most cases, if a person is started on a thyroid medication, they will be taking it for the rest of their lives. There is no cure to make the thyroid gland produce the hormone, once it is no longer functioning properly, but by giving the hormone that the body is used to processing, all functions can be normal again. The price of the medication is not usually an issue, as it is generic and is one of the least expensive medications available. For whatever reason you are thinking of stopping, you may want to reconsider and should consult your doctor about your feelings on this issue. Patti Brown, PharmD
What other drugs will affect Thyroxin?
Many other medicines can be affected by your thyroid hormone levels. Certain other medicines may also increase or decrease the effects of Thyroxin.
Certain medicines can make Thyroxin less effective if taken at the same time. If you use any of the following drugs, avoid taking them within 4 hours before or 4 hours after you take this medicine:
Many drugs can interact with Thyroxin. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed here. Tell your doctor about all your current medicines and any medicine you start or stop using.
Q: I have been diagnosed with hypothyroidism and take levoxythyroxine. I am still gaining weight. Are there some supplements that I can take to help my metabolism? Where can I look to find this information?
A: There are many documented drug interactions between Thyroxin and supplements to lose weight. Therefore, many supplements taken for weight loss are not recommended for people taking Thyroxin or thyroid medication. While weight gain can be a symptom of hypothyroidism, taking Thyroxin does not immediately cause weight loss. Sometimes, it can take a few dosage adjustments before the right dose for each patient is determined. To ensure that you are absorbing the maximum benefit of Thyroxin, take Thyroxin immediately upon arising (first thing in the morning) on a completely empty stomach with at least six to eight ounces of water. Do not lie back down or this may cause reflux. Do not take any other medications, vitamins, coffee, food or liquids other than water for one hour. After one hour then you can eat or drink anything. If after adopting a healthy lifestyle of better food choices and exercise, you are still gaining weight, then you should contact your health care provider for further evaluation. For more information on Thyroxin (Synthroid) and hypothyroidism, please click on the following links. //www.everydayhealth.com/drugs/Thyroxin and //www.everydayhealth.com/thyroid-conditions/evaluating-your-thyroid-disease-risk.aspx Consuelo Worley, RPh
Phenobarbital has been shown to reduce the response to thyroxine. Phenobarbital increases L-thyroxine metabolism by inducing uridine 5’-diphospho-glucuronosyltransferase (UGT) and leads to a lower T4 serum levels. Changes in thyroid status may occur if barbiturates are added or withdrawn from patients being treated for hypothyroidism. Rifampin has been shown to accelerate the metabolism of Thyroxin.
Drugs That May Decrease Conversion of T4 to T3
Potential impact: Administration of these enzyme inhibitors decreases the peripheral conversion of T4 to T3, leading to decreased T3 levels. However, serum T4 levels are usually normal but may occasionally be slightly increased.
Interactions that can make your drugs less effective
When Thyroxin is less effective: When you take Thyroxin with certain drugs, it may not work as well to treat your condition. This is because the amount of Thyroxin in your body may be decreased. Examples of these drugs include:
- Rifampin and anti-seizure drugs such as carbamazepine and phenobarbital.
- Calcium carbonate or ferrous sulfate. Take Thyroxin at least four hours before or after taking these medications to help make sure that Thyroxin works properly.
- Colesevelam, cholestyramine, colestipol, kayexalate, or sevelamer. Take Thyroxin at least 4 hours before taking these medications to help make sure that Thyroxin works properly.
- Simethicone and antacids such as aluminum or magnesium.
- Cancer drugs that belong to the tyrosine-kinase inhibitors class, such as imatinib.
When other drugs are less effective: When certain drugs are used with Thyroxin, they may not work as well. This is because the amount of these drugs in your body may be decreased. Examples of these drugs include:
- Diabetes drugs, such as insulin, metformin, nateglinide, glipizide, and pioglitazone. If you take any of these diabetes drugs with Thyroxin, your doctor may need to increase your dosage of these drugs.
- Digoxin. If you take this drug with Thyroxin, your doctor may need to increase your dosage of digoxin.
- Theophylline. Your doctor may monitor the levels of theophylline in your body if you take it with Thyroxin.
Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs interact differently in each person, we cannot guarantee that this information includes all possible interactions. This information is not a substitute for medical advice. Always speak with your healthcare provider about possible interactions with all prescription drugs, vitamins, herbs and supplements, and over-the-counter drugs that you are taking.