It usually happens at night. You stretch a leg under the covers, point your toes without thinking, and the calf seizes — a hard, visible knot that won't let go for thirty long seconds. Or you stand up from a chair and the arch of your foot locks. You've been eating cleaner and moving less than ever, so a gripping muscle spasm feels like it came from nowhere.

It didn't. Muscle cramps are one of the quieter complaints on Ozempic, Mounjaro, and the other GLP-1 medications, and they tend to show up a few weeks in, right as your appetite bottoms out. The mechanism isn't mysterious once you see what's changed underneath the weight loss. It's mostly a supply problem — and supply problems have fixes.

What a cramp actually is

A true muscle cramp is a sudden, involuntary contraction of a muscle or part of one. The muscle doesn't just tighten; the motor neurons feeding it start firing in rapid, repetitive bursts, well past anything you asked for. Researchers have spent decades arguing over why.

Two explanations dominate, and both probably matter. The older one is the electrolyte-and-dehydration theory: when the fluid around your muscle cells shifts and the balance of sodium, potassium, magnesium, and calcium drifts, the membranes of your nerve endings become more excitable and misfire. The newer one, built largely on studies of cramping athletes, is the altered neuromuscular control theory: fatigue changes the balance between the reflexes that excite a motor neuron and the ones that inhibit it, and the neuron hyperfires on its own.

You don't have to pick a side. What matters is that both pathways are sensitive to the exact things a GLP-1 changes: how much you eat, how much you drink, and how well-mineralized the fluid bathing your muscles is.

Why the medication tilts the odds

Start with intake. GLP-1s work by quieting appetite and slowing how fast your stomach empties. That's the point — but a smaller volume of food is also a smaller delivery system for minerals. Potassium comes largely from produce, beans, potatoes, and dairy. Magnesium rides in on whole grains, nuts, greens, and legumes. Calcium from dairy and leafy vegetables. When your total plate shrinks by a third or more, the electrolytes riding on that food shrink with it, even if what you do eat is perfectly healthy.

Then add the fluid side. Many people on a GLP-1 simply drink less, because the same signals that mute hunger also blunt thirst, and a full-feeling stomach discourages sipping. Nausea, and the vomiting or diarrhea some people hit during dose increases, pull both water and electrolytes out directly — the GI tract is where a lot of your sodium and potassium turnover happens. Lose fluid faster than you replace it and the concentration of minerals around your muscle cells starts to swing.

There's a third, slower factor: the weight loss itself. Rapid fat loss and lower food intake mean less sodium in the diet, which prompts your kidneys to adjust how they hold and dump electrolytes. During that recalibration, the margins get thinner. None of these are dramatic on their own. Stacked together — less mineral intake, less fluid, more GI loss, a shifting kidney set point — they add up to a body running closer to the edge of comfortable neuromuscular stability than it used to.

Why they hit at night

Nocturnal leg cramps have their own logic. When you lie down with the sheets tucked, your foot naturally settles into a pointed, toes-down position. That shortens the calf muscle, and a muscle held in its most contracted range is the easiest one to tip into spasm. Add a body that's slightly under-hydrated and running lean on minerals after a long day of low intake, and the calf is primed. The cramp isn't caused by sleep; sleep just supplies the posture while the day supplied the deficit.

What actually helps — in order

The fixes that work map directly onto the causes, so it's worth doing them in order rather than jumping to a supplement.

Rebuild the plate's mineral density. This is first because it's the root. You're eating less, so every bite has to carry more. Lean toward foods that are quietly rich in the electrolytes you're short on: a banana or a couple of potatoes for potassium, a handful of pumpkin seeds or almonds for magnesium, Greek yogurt for both calcium and protein. You don't need exotic food, you need dense food. This is also where the muscle-protection story and the cramp story overlap — the same protein-forward, whole-food plate that guards your muscle mass on a GLP-1 tends to carry the minerals that keep it from seizing.

Drink to a target, not to thirst. Since thirst is unreliable on these medications, stop waiting for it. Sip steadily through the day and glance at your urine — pale straw is the goal, not clear (clear can mean you're washing minerals out) and not dark. A useful anchor is a full glass with each meal and each dose of medication.

Add electrolytes, not just water. Plain water alone can occasionally make things worse by diluting what's left. If you're sweating, cramping, or coming through a nauseous stretch, a pinch of salt in your water or an electrolyte packet that actually contains potassium and magnesium — not just sodium and sugar — replaces what's leaving. Check the label; many sports drinks are almost entirely sodium.

Stretch the muscle before it stretches you. A slow calf stretch against a wall before bed, and gently flexing your foot upward rather than pointing it, takes the muscle out of the shortened position where cramps start. For an active cramp, pulling your toes toward your shin to lengthen the calf usually breaks it faster than massage.

Where magnesium fits — and where it doesn't

Magnesium gets recommended for cramps constantly, and it's worth being honest about the evidence. In controlled trials on otherwise healthy people with ordinary night cramps, magnesium supplements have performed close to placebo. It is not the guaranteed switch the internet suggests.

But the GLP-1 situation is different from garden-variety cramping, because here there's a plausible reason intake is genuinely low: you're simply eating less of the food magnesium lives in. Correcting a real dietary shortfall is not the same as dosing a mineral you already have enough of. So the reasonable move is to make sure your food supplies adequate magnesium and potassium first, and treat a supplement as backup if cramps persist — ideally after a word with your prescriber, since kidney function and other medications affect how much is safe.

When it's not just a cramp

Most GLP-1 cramping is the benign supply-gap kind. But use judgment. Persistent muscle weakness, cramps paired with a racing or irregular heartbeat, significant swelling, or spasms that come with confusion or severe vomiting are worth a same-day call to your doctor — those can signal an electrolyte disturbance that's moved past the nuisance range, and they're straightforward to check with a blood test. A cramp that resolves in under a minute and leaves a slightly tender muscle is ordinary. One that comes with systemic symptoms is not.

The pattern worth noticing

Step back and the theme is consistent: cramps on a GLP-1 are usually your body telling you that intake — of minerals, of fluid, of food in general — has quietly fallen below what your muscles need to stay calm. It's the same signal that lower lifts, more fatigue, and muscle loss send, just in a form you can feel at two in the morning. Treat the cramp and you get relief tonight. Treat the intake gap and you fix the thing the cramp was pointing at.

That's the harder part, because a suppressed appetite makes "just eat more of the right things" easier said than tracked. Lean was built for exactly this gap — it keeps your protein and the whole-food, mineral-dense meals around it in view when hunger stops reminding you, and pairs that with strength tracking so you can see your muscle holding steady instead of guessing. If the cramps are a hint that your intake has drifted, it's a good moment to make the invisible visible. You can see how it works at https://lean.lumenlabs.works — no pressure, just a clearer picture of what your body is actually getting.