Not everyone qualifies for every weight loss drug. Some restrictions are absolute. Others require careful evaluation. Here's how to tell the difference.
There's a meaningful difference between a contraindication and a warning. A contraindication means "do not use this medication" — it's a hard stop. A warning means "use with caution, monitoring, and informed consent." Most conditions that patients worry about fall into the warning category, not the contraindication category. Understanding which is which can prevent both unnecessary fear and genuine safety oversights.
Section 4 — Contraindications: Hard stops. The medication should not be used.
Section 5 — Warnings and Precautions: Use is possible but requires discussion, monitoring, and medical judgment.
Section 6 — Adverse Reactions: Side effects that may occur during use. Not reasons to avoid starting.
Every FDA-approved GLP-1 receptor agonist (semaglutide, tirzepatide, liraglutide) carries a boxed warning about thyroid C-cell tumors. In rodent studies, GLP-1 agonists caused dose-dependent thyroid C-cell tumors, including medullary thyroid carcinoma. Whether this applies to humans is uncertain — rodents have significantly more GLP-1 receptors on thyroid C-cells than humans do — but the FDA considers the risk sufficient for a boxed warning.
If you have a personal or family history of MTC, or if you have Multiple Endocrine Neoplasia syndrome type 2 (MEN 2), GLP-1 medications are absolutely contraindicated. No exceptions.
Important clarification: this does not mean GLP-1s are contraindicated for general thyroid conditions. Hypothyroidism, Hashimoto's thyroiditis, thyroid nodules (which are found in up to 50% of adults), and even a history of papillary thyroid cancer (which originates from follicular cells, not C-cells) are not contraindications. Your provider should confirm that any thyroid nodules have been evaluated and MTC ruled out, but the presence of thyroid conditions alone does not disqualify you.
Exception worth noting: the older GLP-1 agonists exenatide (Byetta/Bydureon) and lixisenatide (Adlyxin) do not carry the MTC/MEN2 contraindication. Their contraindication is limited to hypersensitivity to the drug itself. Most sites miss this distinction.
A known hypersensitivity to the active ingredient or any excipient in the formulation is a contraindication for all weight loss medications. Anaphylaxis, angioedema, or severe rash on a prior exposure means that drug is permanently off the table. Cross-reactivity between different GLP-1 agonists has been reported rarely, so switching from semaglutide to tirzepatide (or vice versa) may be possible if the reaction was to an inactive ingredient rather than the peptide itself — but this requires allergist evaluation.
No weight loss medication is approved for use during pregnancy. GLP-1 animal studies have shown fetal harm. Topiramate (in Qsymia) is a known teratogen — it causes oral clefts in exposed infants, and Qsymia requires a negative pregnancy test before starting and monthly thereafter through its REMS program. Semaglutide should be stopped at least 2 months before planned conception to allow complete clearance.
Contrave has the most extensive contraindication list of any weight loss medication:
Seizure disorders: Bupropion lowers the seizure threshold. Any history of seizure disorder, anorexia/bulimia (which increase seizure risk), or current use of other bupropion products rules out Contrave.
Current opioid use: Naltrexone blocks opioid receptors. Taking Contrave while on opioids (including opioid pain medications, opioid-containing cough medicines, or medication-assisted treatment for opioid use disorder like methadone or buprenorphine) can precipitate acute opioid withdrawal.
MAOI use: Concurrent use with MAOIs or within 14 days of discontinuing an MAOI is contraindicated due to hypertensive crisis risk.
Abrupt discontinuation of alcohol, benzodiazepines, or barbiturates: These increase seizure risk in combination with bupropion.
Beyond the pregnancy contraindication (stronger here than for other medications due to topiramate's teratogenicity), Qsymia is contraindicated in patients taking MAOIs or within 14 days of MAOI discontinuation (due to the phentermine component), and in patients with glaucoma or hyperthyroidism (phentermine is a sympathomimetic amine).
Contraindicated in chronic malabsorption syndrome and cholestasis (impaired bile flow). Since orlistat works by blocking fat absorption, it's unsuitable for patients who already have fat malabsorption issues.
These conditions don't automatically disqualify you, but they require careful evaluation, monitoring, and potentially modified treatment approaches.
GLP-1 medications have a warning for pancreatitis based on postmarketing reports. However, the causal relationship is not definitively established — obesity itself is a risk factor for pancreatitis, and GLP-1 trials have not shown significantly increased rates compared to placebo when accounting for this. A history of pancreatitis is a warning, not a contraindication. Your provider should weigh the risk-benefit and monitor for symptoms (severe abdominal pain radiating to the back).
GLP-1s slow gastric emptying, which can worsen existing gastroparesis. If you already have significantly delayed stomach emptying, adding a drug that slows it further could cause severe nausea, vomiting, and abdominal distension. Inflammatory bowel disease is another condition requiring careful evaluation — GI side effects from GLP-1s may be harder to distinguish from IBD flares.
Weight loss medications are generally not appropriate for patients with active anorexia nervosa or bulimia nervosa. The appetite-suppressing effects of GLP-1s could reinforce restrictive eating patterns. Binge eating disorder, however, is a different clinical picture — some evidence suggests GLP-1 medications may actually help by reducing food reward signaling. This requires nuanced clinical assessment by a provider experienced in both obesity medicine and eating disorder screening.
GLP-1 medications do not require dose adjustment for kidney impairment, but postmarketing reports have linked them to acute kidney injury — typically in patients who became severely dehydrated from GI side effects (vomiting, diarrhea). If you have chronic kidney disease, your provider should monitor renal function during dose titration and emphasize hydration.
Rapid weight loss from any cause increases gallstone risk. GLP-1 clinical trials showed higher rates of gallbladder-related events (cholelithiasis, cholecystitis) compared to placebo. If you have a history of gallstones or gallbladder disease, this doesn't prevent you from starting treatment, but your provider should discuss the risk and monitor for symptoms (right upper abdominal pain after eating).
The SUSTAIN-6 trial with semaglutide showed a small but statistically significant increase in diabetic retinopathy complications. This is thought to be related to the speed of blood sugar improvement rather than a direct drug effect — rapid glycemic control in patients with existing retinopathy can worsen the condition temporarily. If you have diabetes with retinopathy, you should have an eye exam before starting GLP-1 therapy and monitor more frequently during the first year.
Any provider prescribing weight loss medication should screen for all of the above before your first prescription. If a provider doesn't ask about your thyroid history, current medications, pregnancy status, or history of pancreatitis, that's a red flag. The thoroughness of the intake process is one of the best indicators of provider quality.
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