Weight gain: why it happens and what to do next

Are you noticing clothes getting tighter even though you haven’t changed your routine? Weight gain can sneak up slowly or appear fast — and the cause isn’t always overeating. This page lays out the most common reasons, which medicines often cause weight gain, and practical steps you can use today to slow or reverse it.

Common causes — including medicines that add pounds

Weight changes have many triggers. Some you control (diet, activity, sleep), and some you don’t (hormones, medical conditions, or prescription drugs). Key causes to consider:

- Hormones and health issues: low thyroid (hypothyroidism), Cushing’s syndrome, fluid retention from heart or kidney problems, and hormonal shifts can all lead to weight gain.

- Lifestyle factors: high-calorie drinks, late-night snacking, long stretches of sitting, poor sleep, and chronic stress raise appetite and slow metabolism.

- Medications: several common drugs can cause weight gain. These include corticosteroids (prednisone), some antidepressants and antipsychotics (for example, mirtazapine or olanzapine), certain diabetes drugs like insulin or sulfonylureas, and some mood stabilizers. If you think a medicine is the culprit, don’t stop it — talk to your prescriber about options.

Practical steps you can start right now

Small changes add up. Try these simple, focused actions that actually help without being overwhelming:

- Focus on protein and fiber at each meal. They keep you full longer and reduce snacking. Example: Greek yogurt + berries, or grilled chicken with a big salad.

- Cut liquid calories. Swap sugary sodas, fancy coffee drinks, and fruit juices for water, sparkling water, or unsweetened tea.

- Move more in ways you enjoy. Aim for a mix of brisk walking and two weekly sessions of strength training. Muscle burns more calories at rest and helps reshape your body.

- Improve sleep and stress: aim for 7–9 hours and try short stress tools like 5-minute breathing breaks. Poor sleep and high stress raise hunger hormones.

- Track what matters: a simple food log for 1–2 weeks often reveals easy wins — hidden snacks, big portions, or late-night eating.

- Review your meds with a clinician. If a drug is likely causing weight gain, your doctor might adjust the dose, switch to a different drug, or suggest monitoring strategies.

If you prefer supplements or over-the-counter options, talk them over with your provider first. Some treatments like metformin are used in specific medical situations, but they aren’t a general fix for unexplained weight gain.

See a doctor if you gain a lot of weight quickly, have symptoms like swelling, breathlessness, extreme fatigue, or signs of hormone problems (very cold intolerance, hair loss, purple stretch marks). Unexplained, rapid weight gain deserves prompt evaluation.

Want tailored tips? Check your meds, track food for a week, and bring those notes to your clinician. That makes it easier to find the real cause and fix it without guesswork.