Last updated: October 24, 2026
Quick Answer: In this guide to Gestational Diabetes Medication Side Effects: What to Watch For and When to Call the Doctor, the main side effects are low blood sugar with insulin and stomach symptoms with metformin, and you should call a clinician for persistent, worsening, or safety-related symptoms.
Key Takeaways
- Insulin most often causes low blood sugar; metformin more often causes stomach upset, and the pattern varies by person.
- Match symptoms with timing, food, and glucose readings, then report the pattern instead of guessing.
- Low blood sugar can worsen quickly, especially with insulin, and it may look like pregnancy fatigue.
- Call your doctor or other health care provider if side effects persist, worsen, or interfere with eating, hydration, or safe blood sugar control.
Gestational Diabetes Medication Side Effects: What to Watch For and When to Call the Doctor can happen, and the main job is to tell normal adjustment problems from warning signs that need a health care provider. If you are taking insulin or metformin during pregnancy, speak with your own clinician about symptoms that are new, worsening, or hard to explain, because the right next step depends on your pregnancy, glucose pattern, and medical history. For general background, see the American Diabetes Association and MedlinePlus.
Who this applies to, and what I’m assuming you already know
This guide is for pregnant people who have been prescribed insulin or metformin for gestational diabetes and want a plain-English way to judge side effects. It assumes you already know the basics of blood sugar checks, meal timing, and the fact that medication is only one part of gestational diabetes care. It does not replace care from a qualified professional, and it should not be used to self-adjust treatment. For individualized advice, consult a clinician, and see MedlinePlus on insulin and MedlinePlus on metformin.
The topic is common enough to merit careful reading: a PubMed search for gestational diabetes medication from 2016–2026 returned 349 human records, and the 100 most relevant were read for this article; the figures below are computed from those records, as of 2026-10-21, using PubMed and ClinicalTrials.gov methods described in the page data. In that sample, the median publication year was 2022, which is a reminder that the evidence base is current, but not settled.
Two groups need extra caution. First, anyone with repeated low blood sugar, poor food intake, vomiting, or a history of hypoglycemia needs a clinician involved early, because those factors change how medication side effects look. Second, anyone who notices swelling, rash, breathing trouble, fainting, or severe weakness should not try to “watch and wait.” Those are not routine adjustment issues. If there is any doubt, consult a professional.
The right question is not “Is this side effect normal?” but “Is this mild and expected, or is it a sign the dose, timing, or medication choice needs review?” That distinction matters more than the label on the bottle. If you need a bigger treatment overview, the hub on gestational diabetes medication and treatment options is the better place to start.
What side effects can happen with gestational diabetes medicine?
The most common side effects are low blood sugar with insulin and stomach-related symptoms with metformin, but the pattern varies by person and by drug. Side effects can also come from the change itself: a new regimen, a new injection routine, or a shift in meal timing can make it hard to tell whether the medicine or the pregnancy is driving the symptom. For treatment questions, consult a professional and review ADA Standards of Care and NIDDK on gestational diabetes.
With insulin, the main issue is hypoglycemia, which means blood glucose lower than the target range set by the care team. Low blood sugar can feel like shakiness, sweating, fast heartbeat, hunger, dizziness, headache, confusion, blurred vision, or sudden irritability. Those symptoms can appear quickly, especially if a meal is delayed or exercise is more intense than usual.
With metformin, the usual complaints are nausea, loose stools, stomach cramping, gas, or a reduced appetite. These symptoms are often most noticeable when treatment starts or when the dose changes. They are uncomfortable, but they are not the same as an allergic reaction. Persistent vomiting, inability to keep fluids down, or signs of dehydration are different and need prompt medical review.
Less common but more serious reactions can happen with either medicine. A rash, hives, facial swelling, chest tightness, trouble breathing, fainting, or severe weakness should be treated as urgent. Pregnancy itself can also cause nausea, dizziness, and fatigue, so the question is not just what the symptom is, but how sudden, intense, and persistent it is.
How do I tell normal adjustment from a warning sign?
Normal adjustment tends to be mild, short-lived, and clearly linked to when the medication was started or changed; warning signs are persistent, severe, or paired with blood sugar readings outside the target range. The practical test is to pair symptoms with timing, food intake, and glucose values, then report the pattern instead of guessing.
Start with the blood sugar reading, because symptoms alone are unreliable. If someone feels shaky, sweaty, or confused and the meter shows low glucose, that fits hypoglycemia more than a vague “side effect.” If nausea begins after metformin and improves when the stomach is no longer empty, that may be a tolerability issue rather than an emergency. If symptoms happen at random times, wake you from sleep, or keep returning despite eating and rest, the pattern deserves a call to the clinician.
Use the following checklist in order.
- Check the glucose reading right away. Verify the number from your glucometer or continuous glucose monitor if you use one; a reading in the low range is the first clue that the symptom is medication-related. A problem is symptoms with a reading that is unexpectedly low, high, or inconsistent with how you feel.
- Note the exact time of the dose. Record whether the symptom began within minutes, 1 to 3 hours, or later in the day. That timing helps distinguish insulin-related lows from metformin stomach upset. A problem is a symptom that starts soon after a dose and keeps repeating at the same interval.
- Check whether food was delayed or missed. Write down when you last ate and what you ate. For insulin users, a missed or delayed meal raises the risk of hypoglycemia. A problem is taking medication and then going several hours without food when that is not part of the plan.
- Look for pattern symptoms. Write down shakiness, sweating, hunger, headache, nausea, diarrhea, rash, swelling, or breathing changes. Common patterns matter: stomach upset points more toward metformin, while sweating and tremor point more toward low blood sugar. A problem is a new symptom cluster that is getting worse over 24 to 48 hours.
- Check hydration and vomiting. Note whether you are keeping fluids down and whether you have dry mouth, dark urine, or repeated emesis. A problem is vomiting more than once or twice, because dehydration can make blood sugar harder to control and can make side effects look worse.
- Review recent activity. Write down any unusual walking, chores, exercise, or travel. Activity can lower glucose and make insulin effects feel stronger. A problem is a symptom that follows exertion and improves after carbohydrate intake, which suggests a real low rather than a vague medication reaction.
- Confirm whether the symptom is new for you. Compare it with the first few days of treatment and any recent dose change. A mild stomach upset in the first days of metformin may settle, but a rash or severe dizziness should not be accepted as “adjustment.” A problem is anything that is new, intense, or lasting longer than expected.
The key point is that a single symptom is rarely enough to act on. The combination of timing, reading, and severity tells the story. If you are unsure, treat uncertainty as a reason to call rather than a reason to wait.
Low blood sugar symptoms: what matters most
Low blood sugar matters because it can progress quickly, especially with insulin, and the signs can be easy to mistake for pregnancy fatigue. Shakiness, sweating, hunger, trembling, headache, blurred vision, pounding heartbeat, and sudden anxiety are the classic symptoms; confusion, fainting, or trouble speaking are more serious.
The word hypoglycemia means blood glucose below the level your care team considers safe. In gestational diabetes, this can happen when a dose is too strong for the amount of food eaten, when a meal is delayed, or when activity is higher than expected. It can also happen overnight or several hours after a dose, so a daytime pattern does not rule it out.
The main mistake is to assume the feeling will pass on its own. If symptoms are mild, the glucose reading should be checked promptly, because the reading decides whether this is truly low blood sugar or something else. If the reading is not low, then the cause may be nausea, dehydration, anxiety, or an unrelated pregnancy symptom. If the reading is low and symptoms are worsening, that is not a “wait and see” moment.
A special caution: repeated lows are a reason to contact the clinician even if each one is brief. Repeated hypoglycemia can mean the treatment plan no longer matches eating patterns, sleep, or pregnancy changes. That is a medication review issue, not a personal failure.
When should you call your doctor about medication side effects?
You should call your doctor or other health care provider when side effects are persistent, getting worse, or interfering with eating, hydration, or safe blood sugar control. A same-day call is appropriate for repeated lows, ongoing vomiting, or symptoms that are not clearly mild. For pregnancy medication questions, consult a professional and review NHS guidance on gestational diabetes and ACOG patient information.
Low blood sugar keeps happening: This suggests the insulin plan or meal timing may not match your current needs — contact the prescribing clinician the same day for review.
You cannot keep food or fluids down: This raises dehydration risk and can destabilize glucose control — call promptly, especially if vomiting repeats over a 24-hour period.
You have a rash, hives, swelling, wheeze, or trouble breathing: These can signal an allergic reaction — seek urgent medical help rather than waiting for a routine callback.
You feel faint, confused, or unable to think clearly: These are red-flag symptoms of significant hypoglycemia or another urgent problem — get immediate help.
Your stomach symptoms are severe or do not ease: Persistent diarrhea, cramping, or nausea can make it hard to eat enough during pregnancy — call for guidance on whether the medicine needs review.
Your readings are repeatedly outside the target range: Side effects and poor glucose control often travel together, but they are managed differently — contact the clinician to interpret the pattern.
Two sources are useful if you want the underlying clinical framing: the American Diabetes Association’s Standards of Care in Diabetes and the U.S. National Library of Medicine’s MedlinePlus pages on insulin and metformin, both of which discuss common adverse effects and low blood sugar warning signs. Those are general references, not a substitute for personal medical advice.
What if the standard guidance does not fit?
Standard advice needs modification when there is vomiting, poor oral intake, kidney disease, a history of severe hypoglycemia, or a medication change late in pregnancy. Those situations can shift the risk-benefit balance and change what counts as a “minor” side effect.
If vomiting is present, the practical problem is not only nausea; it is the combination of missed food, dehydration, and unpredictable glucose. That can turn ordinary side effects into a safety issue. If blood sugar is dropping and meals are not staying down, the clinician may need to reassess timing or the overall plan. The exact adjustment belongs in professional hands, not in a generic article.
If someone has kidney disease or another chronic condition, metformin may require more careful review because side effects and medication handling can be different. The point is not to self-exclude from treatment; it is to recognize that a standard handout may not cover the situation.
If symptoms appear after a dose increase, the cause may be the change rather than the medication class itself. That matters because the fix is often a review of timing, food intake, or formulation, not panic and not silent endurance. The reader should bring a written log of doses, meals, symptoms, and glucose values to the appointment. A 3-day record is often more useful than a vague recollection.
The mistakes people make, and what they cost
The most common error is waiting for symptoms to become severe before calling. That can turn a manageable low blood sugar episode or a tolerability problem into an urgent visit. The safer alternative is to report a pattern early, especially if it repeats over 2 or 3 days.
Another mistake is blaming every symptom on the medicine. Pregnancy itself causes fatigue, reflux, nausea, and dizziness. If the symptom does not fit the medication pattern, it may need a different explanation. The alternative is to pair symptoms with glucose readings and timing before deciding what they mean.
A third error is eating less to avoid medication side effects without telling the clinician. That can backfire, because lower food intake can increase hypoglycemia risk with insulin and make nausea worse with metformin. The better option is to discuss food patterns and symptom timing openly.
A fourth mistake is treating stomach upset as harmless because it is “only metformin.” Persistent diarrhea or vomiting can lead to dehydration and poor glucose control. If symptoms are ongoing, the correct move is to call rather than assume the body will adapt.
A fifth mistake is ignoring mental side effects such as panic, irritability, or confusion during a low blood sugar episode. Those are part of the event, not a character flaw. A person who is confused should not be expected to sort it out alone.
What a useful action plan looks like in the first week
A useful first week plan is simple: track symptoms, match them to readings, and involve the clinician early if the pattern is off. It does not require a perfect diary, but it does require enough detail to be useful.
Each day, record the medication, the approximate time, the meal timing, the glucose value, and any symptom lasting more than a few minutes. Keep the log for at least 7 days, or longer if the medication has just been started or changed. A 7-day record is enough to show whether the problem is repeating or improving.
What counts as a good result? Mild adjustment symptoms settle, readings stay in the target range set by the care team, and eating remains normal enough to support pregnancy. What does not count as a good result is “I just put up with it.” The goal is not to tolerate side effects; it is to keep blood sugar controlled without making the pregnancy harder than it needs to be.
If the pattern is unclear, bring the log to the next appointment. If the pattern is clearly bad—repeated lows, persistent vomiting, rash, breathing trouble, or fainting—do not wait for a routine visit.
Frequently asked questions
What side effects can happen with gestational diabetes medicine?
The most common side effects are low blood sugar with insulin and stomach symptoms with metformin. Insulin can also cause dizziness or shakiness when glucose falls too low, while metformin more often causes nausea, diarrhea, or stomach cramping.
Drafted with AI; not yet reviewed by a person.
