Everything about these medications gets such enthusiastic coverage that I want to spend a whole post on the part nobody puts in an ad: who shouldn't take them, or should proceed with real caution. This is the unsexy side of prescribing, and it's also where good medicine actually lives. Saying "yes, this is right for you" only means something if the same clinician is willing to say "no, this isn't safe for you," and means it. So here's the no list, and the proceed-carefully list.
Let's begin with the hard stop signs, the genuine contraindications. GLP-1 medications carry a warning related to a rare type of thyroid cancer, medullary thyroid carcinoma, based on findings in animal studies. Because of that, they are not used in people with a personal or family history of that cancer, or in people with a genetic condition called MEN2 that raises the risk of it. This is something we screen for carefully and deliberately, and it is not a rule we bend. If that history is in your family, this class of medication is off the table, full stop, and a prescriber who doesn't ask about it is skipping something that matters.
Next, a history of pancreatitis. This calls for real caution and a genuine conversation, not a casual green light, because these medications have been associated with pancreatitis in some cases. The same careful thinking applies to serious gallbladder disease, partly because rapid weight loss of almost any kind can increase the risk of gallbladder problems, and these medications can drive significant weight loss. None of that is an absolute "never" for everyone in every case, but it's firmly in the "we need to talk about this seriously and weigh it carefully" category.
Pregnancy and breastfeeding are another clear boundary. These medications aren't appropriate during pregnancy or while breastfeeding, and we generally recommend stopping them well before a planned pregnancy. So if you're someone who could become pregnant, that's not a footnote, it's an important and specific part of the discussion, and it deserves real attention rather than a passing mention.
There are also conditions that don't necessarily rule the medication out but demand extra thought. People with certain severe gastrointestinal conditions, including significantly delayed stomach emptying, may not be good candidates, because these medications slow digestion even further, and stacking that slowdown on an already-impaired system can cause problems.
And then there's a whole layer beyond the formal contraindications, the situations that simply require careful, individualized thought rather than a checklist. Certain other medications you take, which can interact or compound effects. Other health conditions in the mix. Your personal history with food and eating, which genuinely matters here and is too often skipped. And the practical question of whether you'll be able to maintain adequate nutrition on a significantly reduced appetite, because eating too little of the wrong things while not hungry is its own risk.
I want to be clear that I'm not laying all this out to frighten anyone away from a medication that helps a great many people. The vast majority of appropriate candidates do well, and I prescribe these regularly and gladly. The entire point of this post is different: it's that "appropriate candidate" is a real, meaningful category, determined by a thorough history and a careful conversation, not a box that everyone automatically fits into just because they want to lose weight. The screening isn't a bureaucratic hurdle between you and the medication. It's the thing that keeps the medication safe.
So let me turn this into something practical you can actually use. If you're considering a GLP-1, expect a real screening, and frankly, be suspicious if you don't get one. A responsible prescriber should ask about your thyroid history and your family's, your pancreas, your gallbladder, your pregnancy plans, your full medication list, and your relationship with eating. If someone is ready to hand you one of these off a quick online quiz and a credit card, with none of those questions asked, that should worry you, not reassure you with its convenience. The caution is a feature, not a hassle. It's how you can tell the difference between someone treating you as a patient and someone treating you as a sale.